Knee actions and strength predictors of ball release speed amongst fast bowlers in cricet

KNEE ACTIONS AND STRENGTH PREDICTORS OF BALL RELEASE SPEED AMONGST FAST BOWLERS IN CRICKET

by

SAJEEL CHAUDHRY

June 2015

A RESEARCH PROJECT

Submitted in partial fulfilment of the requirements for the degree

MASTERS OF SCIENCE STENGTH & CONDITIONINGST. MARY’S UNIVERSITY

ABSTRACT

A more extended knee angle at front foot contact (FFC) is a technique variable which is known

to be moderately to strongly correlated with the release speed of the ball. Previous literature has

proposed that a straighter knee is able to resist flexion due to its greater eccentric capacity

whereas a knee which is able to extend after front foot contact has a greater concentric capacity.

The aim of the study was to characterise the relationship between the various types of knee

actions and eccentric and concentric capacity of the knee musculature via isoinertial strength

assessments amongst fast bowlers. Participants were male right handed club bowlers (n = 20,

Age 24.3 ± 5.6 years, mass 76.4 ± 9.3 kg and height 1.79 ± 0.06 m). A high speed video camera

operating at 250 Hz was used to measure the release speed of the ball and group bowlers

according to the types of knee actions. Independent t-tests revealed that there was no significant

difference in the release speeds of the ball or in the strength assessments of countermovement

jump (CMJ), squat jump (SJ) and 1 RM (% body weight) eccentric squat between the groups.

The results highlighted that bowlers with a straighter knee action did not possess a greater

eccentric capacity nor did the knee action which extended possess a greater concentric capacity.

However there was a significant (p<0.05) difference in the RSI scores between a flexed knee

(1.06 ± 0.15) and the knee action which flexed and then extended (1.26 ± 0.17) upon FFC,

revealing that bowlers who flexed and then extended possessed a better stretch shortening cycle

quality compared to other knee actions. A backward stepwise multiple linear regression analysis

revealed the 1 RM (% body weight) eccentric squat as a single significant predictor variable (r =

0.47, p = 0.04) explaining 22% of the variance in the release speed of the ball.

Keywords: Male fast bowlers, high speed video, front foot contact, delivery stride, isoinertial

strength assessments

TABLE OF CONTENTS

ABSTRACT....................................................................................................................................ii

LIST OF TABLES..........................................................................................................................iv

LIST OF FIGURES.........................................................................................................................v

INTRODUCTION...........................................................................................................................1

METHOD......................................................................................................................................10

Participants........................................................................................................................10

Categorisation of Knee Actions.........................................................................................11

High Speed Camera Analysis for Measuring Release Speed and Knee Angle.................13

Bowling Session................................................................................................................20

Strength Assessments........................................................................................................20

Statistical Methods.............................................................................................................24

RESULTS......................................................................................................................................25

DISCUSSION................................................................................................................................32

REFERENCES..............................................................................................................................44

iii

LIST OF TABLES

Table 1. Four distinct stages in a bowler’s action............................................................................5

Table 2. Correlation between knee angle and ball release speed at front foot contact....................6

Table 3. Lower limb strength measurements and release speed of ball...........................................7

Table 4. Bowlers grouped according to the 3 types of knee actions..............................................12

Table 5. Speed measurement of bowling machine with high speed camera.................................17

Table 6. Bowling speed inaccuracies within crease (Camera 10.80 m away)...............................18

Table 7. High speed camera calibration out of plane from bowling line.......................................19

Table 8. Comparison of strength assessments...............................................................................21

Table 9.Mean and Standard Deviation of Performance Variables (where n=20)..........................25

Table 10. Correlation Coefficient (r) for Release Speed vs. Performance Variables (n=20)........25

Table 11. Knee action type and number of participants in each group..........................................26

Table 12. Studies investigating correlation of knee angle with release speed of the ball..............33

Table 13. Anthropometric and strength predictors amongst junior and senior bowlers................35

Table 14. Comparison of current study with previous studies on knee action and release speeds37

Table 15. Classification of bowlers according to release speed....................................................40

Table 16. Relationship between run up speed and release speed of the ball.................................41

iv

LIST OF FIGURES

Figure 1. Top bowling speeds to date in international cricket (Cric Info: ESPN Cricket)..............2

Figure 2. ACB report on injury rate against player workload between 1996 - 2002.......................3

Figure 3. SMA report on injury rate against player workload between 1999 - 2006......................3

Figure 4. High speed camera set up to measure release speed of ball...........................................15

Figure 5. Accuracy of bowling machine with distance away from high speed camera.................16

Figure 6. Set up to measure bowling speed errors within crease...................................................18

Figure 7. Calibration of objects in background or foreground for release speed..........................19

Figure 8. Significant correlation between 1 RM (% BW) and release speed of the ball...............26

Figure 9. Group A release speed vs. knee angle (r=0.98, t=6.34, α=0.05)....................................27

Figure 10. Group B release speed vs. knee angle (r=-0.33, t=-1.10, α= 0.05)...............................27

Figure 11.Group C release speed vs. knee angle(r = -0.22, t = -0.39, α = 0.05)............................28

Figure 12. Comparison of release speed of the ball between groups.............................................28

Figure 13. *Significant difference in mean RSI between Group B and C (t = -2.50, p<0.05)......29

Figure 14. Comparison of mean values of CMJ between groups.................................................30

Figure 15. Comparison of mean values of SJ between groups.....................................................30

Figure 16. Comparison of mean values of 1RM (% BW) between Groups..................................31

v

INTRODUCTION

Fast bowlers are considered critical components to the success of the teams by dismissing batsmen due

to their sheer speed, bowling in excess of 85mph (Bartlett, Stockill, Elliot & Burnett, 1996). As a result

fast bowling is biomechanically the most highly studied area in cricket as research continues to explore

the factors that contribute to the increase in the release speed of the ball and because of the high injury

rates associated with the action, particularly spinal related (Foster et al., 1989, Elliot, 2000). Studies

have been conducted understanding factors such as technique, anthropometric and strength which show

significant correlation with the release speed of the ball (Pyne et al., 2006; Wormgoor, Harden &

McKinon, 2010; Worthington, King & Ranson, 2013a). Various aspects of the bowling technique have

been identified that are correlated with the release speed of the ball such as run up speed, trunk flexion,

knee angle, shoulder angle and ground reaction forces at front foot contact (Worthington et al., 2013a;

Worthington et al., 2013b). Similarly strength relationships have also been investigated with the release

speed of the ball (Wormgoor et al., 2010; Loram et al., 2005), however no interaction between

technique and strength variables has been investigated in order to understand the model of physical

fitness which is specific to a sport (Verkhoshansky & Siff, 2009) allowing the design of strength

training programs more specific to the performance enhancements of fast bowlers.

Due to limited knowledge of the interaction between technique and strength variables with the release

speed of the ball, there is scarce coaching application available in improving the performance of fast

bowling by increasing the release speed (Worthington et al., 2013a). Though there is limited scientific

literature investigating the relationship of technique related coaching interventions and any impact to

the release speed of the ball, anecdotally it is considered that the bowling speed at the international

level has not really increased over time and has stayed within a range since the 1970’s (Robinson,

2013; Brenkley, 2012) despite the introduction of more specific and scientifically designed training

programs for fast bowlers (Woolmer & Noakes, 2008; Noakes & Durandt, 2000). Figure 1 shows the

1

top bowling speeds recorded by year at international level according to ESPN Cricket (2008), however

the methods of measuring these speeds have varied, using video footage or different types of radar guns

to calculate the speed of the ball.19

75

2000

2002

100110120130140150160170

Bowling Speed (KPH) Linear Slope of Bowling Speed (KPH)

Time (Year)

Bow

ling

Spee

d (K

m/h

)

Slope (m) = 0.03

Figure 1. Top bowling speeds to date in international cricket (Cric Info: ESPN Cricket)

Bearing in mind the range of bowling speeds at international level it appears that improved physical

conditioning hasn’t contributed to increasing the bowling speeds over time despite the introduction of

enhanced training programs at the elite level (Woolmer & Noakes, 2008). Though there isn’t any

scientific evidence to justify this relationship, there are indications to support such claims. The increase

in physical demands and injury rates over time amongst fast bowlers may provide some indication to

the increased physical condition of players over time.

The physical demands of fast bowling have increased steadily due to the increased match schedules at

domestic level by an average 10% year on year from 1996 to 2002, and at international level by an

average of 2% year on year from 1999 to 2006 in Australia (Orchard, James & Portus, 2006; Orchard

& James, 2002). Injury rates on the other hand have stayed relatively stable at both domestic and

international level in Australia with an increase of 1% year on year (Orchard, James & Portus, 2006;

2

Orchard & James, 2002). Figures 2 & 3 show the match load against injury rates from the cricket board

reports.

1996 1997 1998 1999 2000 2001 20020

50010001500200025003000350040004500

0

5

10

15

20

25

30

Player Hour Exposure Injury/10000 player hour

Season

Play

er H

our E

xpos

ure

Inju

ry/1

0000

pla

yer h

our

Figure 2. ACB report on injury rate against player workload between 1996 - 2002

1999 2000 2001 2002 2003 2004 2005 200614000145001500015500160001650017000175001800018500

0

5

10

15

20

25

30

35

40

Player Hour Exposure Injury/10000 player hour

Season

Play

er H

our E

xpos

ure

Inju

ry/1

0000

pla

yer h

our

Figure 3. SMA report on injury rate against player workload between 1999 - 2006

Though the above injury rates comprise of all roles and activities within cricket, fast bowling is the

activity which is most affected by injuries accounting for over 41% of the total injuries (Gregory, Batt

3

& Wallace, 2004; Stretch, 1993). Amongst fast bowlers the most common stages of injury are the

delivery stride & follow through, and overuse or increased bowling workload, both accounting for 26%

and 19% respectively, according to a study conducted by Stretch and Venter (2003). These injuries

comprise mainly of muscle strains & tears (38%), spasms (8%), ligament tears (2%), tendonitis (7%)

and rotator cuff injuries (3%), which can all be prevented by via the use of physical conditioning

programs (Heidt, Sweetnam, Carlonas, Traub & Tekulve, 2000).

The risk of injury amongst fast bowlers is dependent upon technique, physical preparation and bowling

workload (Dennis, 2007; Dennis, Finch & Farhart, 2005) which can be displayed as a linear equation:

Injury Rate = Technique + Physical Preparation + Bowling Workload (Equation 1)

From data reported previously, injury rate has remained relatively stable despite the increased

workloads over the years amongst cricketers. Thus by observing Equation 1, for injury rates to remain

stable either technique or physical preparation must have improved or both. Very little is known about

altering the bowling technique amongst fast bowlers, as only a handful of studies have investigated the

efficacy of modifying a fast bowling technique or action (Wallis, Elliot & Koh, 2002; Elliott and

Khangure, 2002; Ranson, King, Burnett, Worthington & Shine, 2009). These studies have shown that

there are certain aspects of a bowling action that can be changed amongst junior bowlers, such as the

amount of shoulder rotation at back foot contact and more side on shoulder alignment in order to

reduce injuries related to the spine as Stretch and Venter (2003) have reported a reduction in injury due

to micro trauma and stress fractures amongst junior fast bowlers in South Africa by administrating

correct and safe bowling techniques. However its effectiveness to in elite bowlers is yet to be

determined as the actions are highly developed. Thus the relatively stable rate of injury amongst the

elite level maybe associated with the improved physical condition of bowlers over time, though

improved technique may also be a contributing factor as very little is known about it.

4

Despite the indications that physical conditioning has improved with the advancements in training

programs, it appears that the transfer phenomenon to bowling performance due to training stimulus is

not effective in increasing the release speed of the ball. With a lack of knowledge and studies

conducted in understanding the relationship between technique and strength variables, there appears to

be a gap in understanding the dominant bio motor abilities in fast bowling. As a result adaptations due

to training stimulus which are not aimed at specifically enhancing these bio motor abilities diminish as

sporting proficiency increases (Verkhoshansky & Siff, 2009). Thus improvements in performance are

determined mainly by the ability to target specific motor abilities as dictated by the sport (Bompa &

Haff, 2009) as athletes become more skilful.

In order to understand the technique variables that are linked to the release speed of the ball, various

investigations have been conducted by identifying the three types of actions within fast bowlers (front

on, side on and mixed) along with the four distinct stages in a bowling action (Worthing et al., 2013a;

Elliot & Foster, 1986; Liebenberg, 2007; Bartlett et al, 1996). These stages and further elements in a

bowling action investigated are summarised in Table 1.

Table 1. Four distinct stages in a bowler’s actionStage Elements investigatedRun up speed, length, rhythmPre delivery strideDelivery stride back foot strike, front foot strike, stride length and

alignment, front knee angle, shoulder and hip orientation, non bowling arm, trunk, the ball release

Follow through

The delivery stride has been an area of great focus and a greater knee angle (extended) at front foot

contact (FFC) is a variable which has received much attention and is believed to be moderately to

strongly correlated to the release speed of the ball according to studies shown in Table 2.

Table 2. Correlation between knee angle and ball release speed at front foot contactAuthor r value P value

5

Wormgoor et al. (2008) r = +0.52 P = 0.005Burden & Bartlett. (1990) r = +0.41 P = 0.02

Loram et al. (2005) r = +0.71 P = 0.011

Studies have further broken down this relationship into knee actions based on common movement

patterns observed amongst fast bowlers (Bartlett et al., 1996; Portus et al., 2000; Portus et al., 2006).

Though there are subtle variations in the categorization of these knee actions, it is acknowledged that

there are three types of knee actions. The first is where the bowler lands with almost a fully extended

knee known as a straight leg at front foot contract (knee angle >150º). The second type of knee action

is where the bowlers land with a flexed knee (knee angle <150º). The third type of knee action has been

identified as the bowler flexing the knee at front foot contact however then extending to almost a fully

extended knee or straight leg action.

There are a number of reasons why a greater knee angle at FFC is thought to increase the release speed

of the ball. Elliot, Foster and Gray (1986) state that a greater knee angle increases the tangential

velocity of the ball, as it is released, due to a greater lever arm from the front foot to the arm as the

radial distance is increased. According to Portus et al. (2004) a more stable platform is provided when

the leg is straighter as the leg is stiffer allowing a more effective transfer of kinetic energy from the

momentum of the run up. Thus it is essential for the knee musculature to resist flexion upon FFC which

is dependent upon its eccentric ability whereas extension of the knee is a function of its concentric

capacity (Wormgoor et al., 2010).

A number of studies have investigated the relationship between lower limb strengths and release speeds

as shown in Table 3, however these studies have inconclusively been able to establish strength

predictors of release speed of the ball. This may be due to the selection of the types of strength

assessments, as only one study has used isoinertial strength tests which has a close correspondence to

sporting movements that include closed kinetic chain type of movements (Meylan, Cronin & Nosaka,

6

2008) and a strong correlation with dynamic sporting movements and performance (Cronin & Hansen,

2005).

Table 3. Lower limb strength measurements and release speed of ballStudy Test Results Comments

Wormgoor et al. (2010) Isokinetic strength test of knee flexion/extension

No significant correlation between isokinetic knee

strength

Negative correlation between increased knee

flexion and release speed, implied knee needs to

resist flexionPyne et al. (2006) Isoinertial strength test

(Counter Movement Jump)

Moderate significance between senior and

juniors with large effect size (1.4)

Release speed was greater for greater lower limb

strength tests

Loram et al. (2005) Knee extension/flexion peak torques

No significant relationship (extension r

= -0.11, flexion r = -0.08)

Positive correlation between knee angle and

release speed however no strength predictors

Studies have also failed to address the relationship between the knee strength and the type of knee

action. Instead statistical analysis has been performed with the knee action and release speed of the

ball. Thus there is no evidence to suggest that a straighter knee does possess more eccentric ability

whereas a knee that is able to extend after front foot contact possesses more of a concentric ability.

Having such evidence would also expose the issue whether knee flexion is a function of technique or

strength, as a study by Ranson et al. (2009) showed that knee angles have not known to change despite

coaching interventions over a period of two years, and thus there is a possibility that strength training

programs may be able to impact a change in knee angle at front foot contact.

Interestingly literature so far has failed to investigate another possible bio-motor ability explaining the

concentric action of the knee and a greater correlation with the release speed of the ball (Portus et al.,

2004). According to Wormgoor et al. (2010) the knee action which flexes and then extends upon front

foot contact has more concentric strength in the knee musculature. The time to peak force within a

bowling action is 0.16 secs from FFC (Hurion et al, 2000) which is within the fast stretch shortening

cycle of <0.25 secs (Wilson & Pryor, 1994) where the knee flexes in order to decelerate the body,

7

storing elastic energy, and then extending releasing the stored elastic energy which contributes to the

power development in the concentric phase (Turner & Jefferys, 2010). Thus it is possible that the knee

action which flexes and then extends has a greater stretch shortening cycle score than the other knee

actions.

Thus based on the models presented, and the lack of understanding of these various knee actions and

strength relationships, this study shall aim to test the below hypotheses in order to characterise these

strength technique relationships:

H1: Bowlers with an extended knee on FFC technique have stronger eccentric capacity of the knee

musculature.

H2: Bowlers who flex and then extend their knee on FFC have greater concentric capacity of knee

musculature.

H3: The stretch shortening cycle is stronger in the knee action which flexes and then extends at FFC.

Below is a flow diagram of how to test the above hypotheses for this study:

8

Analysis and categorisation of types of knee actions (Grouping and knee angles)

Evaluation of Strength assessment & selection

Analysis of methods to use for bowling analysis using high speed camera

Protocols to use for strength assessments

Calibration, error analysis & recommendations of use of high speed cameras

Strength assessments of bowlers

Biomechanical and video analysis of bowlers (knee angles & release speed)

Hypotheses analysis, discussion & conclusion

9

METHOD

Participants

20 male right handed bowlers (Age 24.3 ± 5.6 years, mass 76.4 ± 9.3 kg and height 1.79 ± 0.06 m)

from premier division clubs in the Shepherd and Neame League Essex participated voluntarily in the

study. St. Marys University, Twickenham, London Ethics Committee approved of all the procedures

and informed consent before the study commenced. Participants were required to attend three sessions

as below in the following order:

1. Bowling session – Use of high speed cameras to measure knee angle and release speed of the

ball

2. Familiarisation session – Techniques for the strength assessment

3. Strength assessment session – Collection of data for strength assessment

Prior to the study the participants were provided with participant information letters (Appendix B) and

were briefed in regards to the risks associated with the project. Consent forms (Appendix C) were

signed and medical questionnaires (PAR-Q- Appendix D) were filled to assess the physical condition

of the participants in order to participate in the study.

During the data collection period, participants were informed not to participate in any strength and

conditioning activities which would confound the results of the study due to neuromuscular and

physiological adaptations. Similarly the participants were required to attend the strength assessment

session within two weeks of the bowling session mitigating any detraining effects (Garcia-Pallares,

Sanchez-Medina, Perez, Izquierdo-Gabarren & Izquierdo, 2010) due to any potential loss in

neuromuscular and physiological performance. Also a time frame of seven days was provided in

between the familiarisation session and the strength assessment session, allowing ample time to

10

dissipate any gains in neuromuscular and physiological adaptations according to the General Adaptive

Syndrome (GAS) according to Verkhoshansky and Siff (2009). The aim of the familiarisation session

was to develop skill in order to perform the required technique which is important when performing

isoinertial strength tests (Mayhew, Ball & Arnold, 1989; Reynolds, Gordon & Robergs, 2006).

Categorisation of Knee Actions

Knee actions were categorised into three main groups. If the knee is extends to an angle greater than

150º at front foot contact and remains extended is considered a straight leg. This is based on

recommendations from Elliot, Foster & Gray (1986) that a minimum angle of 150º is sufficient in

maximising the release speed of the ball as it provides a stable lower body to act as an effective lever.

Evidence of bowlers with this type of knee action is present from studies by Mason et al. (1990), Elliot

& Foster (1984) and Portus et al. (2000) where the knee angles have been greater than 173º. This type

of knee action can also involve further extension after front foot contact, however no flexion is

observed. Thus a straight leg action is considered where the knee lands at an angle greater than 150º,

does not flex and then either remains at that angle or extends further.

The flexed knee technique occurs when the knee is less than 150º at release of the ball at front foot

contact. At front foot contact the knee maybe greater than 150º however then flexes to stabilise to less

than 150º at release of the ball. This is based on studies by Elliot et al. (1986) where on average

bowlers landed at 158º at front foot contact however flexed by 29º by release of the ball. A study by

Portus et al. (2000) showed that bowlers landed with a knee angle of between 129º-139º however no

details of whether the knee flexed further upon front foot contact. Thus the criterion for a flexed knee

action is that the knee angle is less than 150º at release of the ball irrespective of where the knee was at

FFC.

11

The third type of knee action flexes upon front foot contact, however extends to a straight leg technique

i.e. > 150º till the release of the ball. A study by Burden & Bartlett (1990) showed that three out of the

seven elite bowlers landed with a mean knee angle 173º ±3º then flexed their knee by a mean of 6.6º

and then extended till release of the ball to a mean angle of 173º±11º. Whereas amongst the college

bowlers only one out of the nine bowlers flexed the knee by approximately 31º and then extended to an

angle of approximately 166º. Similarly Stockill & Bartlett (1992) and Burden (1990) showed that a few

bowlers flexed their knee upon contact and then extended to an angle greater than 150º, which is a rare

action amongst fast bowlers. Thus the criterion for this type of knee action is that it flexes after front

foot contact, irrespective of what the initial knee angle is, and then extends to an angle greater than

150º at the release of the ball i.e. becomes a straight knee action.

Based on the literature bowlers were grouped into three categories with the criteria summarised in

Table 4.

Table 4. Bowlers grouped according to the 3 types of knee actionsGroup Knee action Criterion

Group A Straight Leg Knee at FFC> 150º, does not flex but may extend

till releaseGroup B Flexed Knee Knee flexes

irrespective of start at FFC and is < 150º at release

Group C Knee flexes and then extends Knee flexes irrespective of start at FFC,

then extends to > 150º at release

12

Data Collection for Release Speed and Knee Angle

The bowling analysis took place in an indoor sports hall. Lake Image Systems Fastec In-Line 1000

mono-chrome high speed camera with a resolution of 640*680 and a 6 mm lens was used to record the

knee action and measure the release speed of the ball, by placing it perpendicular to the popping crease,

mounted on a Dynasun EL9901 tripod. The camera operated at 250Hz which is in line with other

studies which have used a minimum operating frequency of 200Hz (Burden & Bartlett, 1990; Stockill

& Bartlett, 1992; Worthington, King & Ranson, 2013a). However most studies into biomechanics of

fast bowlers have used a high speed camera to analyse joint kinematics and not the release speed of the

ball (Worthington, King & Ranson, 2013b; Ranson, Burnett, King, Patel & O’Sullivan, 2008;

Worthington et al., 2013a; Glazier, Paradisis, & Cooper, 2000; Pyne et al., 2006; Wormgoor, Harden &

McKinon, 2010). These studies have used radar guns which point towards or away from the bowler in

line with the stumps to measure the speed of the ball. Radar guns use the principle of the Doppler shift

to measure the speed of a moving object (Kaur & Kaur, 2013) and generally are two types. A fast gun

measures the speed within a few feet of the ball being released i.e. release speed, whereas a slow gun

measures the speed after 20-25 feet of the ball being released i.e. average speed. Though studies in fast

bowling speed measurement have not stated the type of speed gun used, there are indications that they

have used fast guns in order to measure the release speed and not average speed. In a study by Glazier

et al., (2000) the radar gun was adjusted to reject any speeds less than 16 m/s in order to cancel out any

influences of limb velocities. Unless adjusted fast guns are known to pick up false targets such as limb

motion as it is trying to measure the speed of the ball very close to the bowler. Also release speed is

important as this is the maximum velocity of the ball as it is measured just as the ball leaves the

bowlers hand. According to Adair (1991) the velocity of a baseball decreases over its trajectory due to

resistance caused by air drag and the velocity of the ball can decrease by 0.21 m/s for every 1m the ball

travels.

13

Fast radar guns are expensive to buy with prices ranging from $750- $5600 and require inputs such as

distance to bowler and often require a trigger control i.e. someone constantly operating it. For a

strength and conditioning coach, budgetary and resource constraints are often the case and hence the

study used the high speed camera to measure the release speed of the ball. Worthington et al., (2013a)

used a similar approach in measuring the release speed and measured the distance the ball travelled

between the first frame, when the ball was released, to about 10 frames after at approximately 0.033

secs. However the study used a motion tracker, to measure the velocity of the ball, which is digitised

software to measure an objects kinematics. Such software cost in the region of $6000-$15000 and may

not always be accessible for strength and conditioning coaches, and thus using relatively simple

distance/time calculations were used to measure the release speed of the ball. This method requires a

calibration process before each session via the following steps:

1. Place two objects, at a measured distance away from each other, on the same plane as where the

bowler shall be releasing the ball. During the study two poles were spaced at 2.74 m, on the

same plane as where the bowlers would be bowling, mid-distance between the stumps and the

return crease as illustrated in Figure 4

2. Using the high speed camera, record this steady state with the poles in focus (The camera must

not be moved from its designated position at all times during the session, nor must any of the

settings be changed)

3. Using the high speed camera’s proprietary software, playback the above recording and measure

the distance of the poles on the player (During the study this was measured to be 34.92 mm

using a Vernier calliper)

4. Use ratio’s to estimate the actual distance of the object moving on same plane i.e. Real

Distance/Playback Distance (Ratio = 2740/34.92 = 78.46)

5. If the ball travels 5mm on the playback screen it actually travels 0.39m (5*78.46/1000)

14

Return Crease

Stum

ps

62cm

62cm

6. If the ball travelled 5mm in 0.033 secs on the playback then the velocity of the ball was 11.88

m/s (Distance/Time = 0.39/0.033)

In order to assess the accuracy of using high speed cameras in measuring the release speed of the ball, a

Bola bowling machine was used and set to a pace of 70 mph. The projectiles of the bowling machine

were recorded and then the speeds calculated as described previously. The bowling machine was

placed at three different positions as there were three pitch markings in the sports hall. Pitch A was

4.95m from the high speed camera, and pitch B and C were 8.17m and 10.80m respectively as

illustrated in the Figure 5.

15

Figure 4. High speed camera set up to measure release speed of ball

Cam

era

4.95m

8.17m

10.80m

16

A

B

C

Figure 5. Accuracy of bowling machine with distance away from high speed camera

Return Crease

F

From the results in Table 5 it can be seen that the further away the camera is placed from the travelling

object, the more accurate the velocity measurements due to reduction of the effect of the lens curvature.

However the measurements recorded by the high speed camera are generally higher and this can be

associated to the limited resolution of the high speed camera used, low lighting conditions and an

operating frequency of 250 Hz (Theobalt et al., 2004). A study by Smith, Broker and Nathan (2003)

reported ball speeds of up to 8% higher when recorded by high speed cameras as compared to a radar

gun as the trajectory of the ball was not linear or same plane as the camera. However it may also be

pointed out that there is no information available in regards to how the bowling machine is calibrated

and the manufacturer provides an accuracy of ± 2 mph, hence errors also exist within the speed of the

bowling machine.

Table 5. Speed measurement of bowling machine with high speed camera

Pitch PositionBowling machine

Speed (mph)High speed camera measurement (mph)

Speed difference (mph)

% difference

A 70 ±2 73.00 +3.00 +4.29%B 70 ±2 72.46 +2.46 +3.51%C 70 ±2 72.13 +2.13 +3.04%

Another error during the calculation of the release speed is associated with the ball moving in a

different plane as to where the two objects are placed. Coaches must be aware of these errors during

studies, though bowlers may be specified to bowl in the same plane as the objects during the set up,

there are errors associated with bowlers landing and releasing the ball anywhere in between the stumps

and the return crease. The amount of error was quantified by placing the objects as illustrated in Figure

4 and using a bowling machine which was filmed on the stumps, between the stumps and return crease

and at the return crease, positions D, E & F respectively as illustrated in Figure 6 with the results in

Table 6.

17

Table 6. Bowling speed inaccuracies within crease (Camera 10.80 m away)Pitch Position Bowling machine



% difference

D 70 ±2 67.07 -2.93 -4.18%E 70 ±2 72.13 +2.13 +3.04%F 70 ±2 76.74 +6.74 +9.63%

(Approximate error of ±7% if the speed at pitch position E is normalised value of bowling machine)

The results in Table 6 also highlight how important it is to calibrate on the same plane as the bowlers

and not to take any measurements of objects for reference in the background or foreground. In order to

show the significance of measuring the velocity of a moving object in the same plane as the fixed

objects, the bowling machine was placed two meters to the left and right of the stumps where the

objects were placed as illustrated in Figure 7. The results in Table 7 indicate how significant the errors

can be if the calibration is performed to a different plane as to where the bowlers release the ball.

Table 7. High speed camera calibration out of plane from bowling linePitch Position Bowling machine



% difference

2m (left) 70 ±2 81.96 +11.96 +17.09%Middle Stump 70 ±2 72.13 +2.13 +3.04%

2m (right) 70 ±2 59.56 -10.44 -14.91%

18

Stum

ps

2m2m

Cam

era

Thus after performing the calibration before each session and recording the bowling actions 10.80 m

away from the camera, the release speed of the ball was measured 10 frames after the first frame where

the ball was released at 0.04 secs. The knee angles were measured using a protractor by identifying

features closely related to the ankle, knee and hip on the cameras playback software and a vernier

calliper to measure the distance on the playback monitor.

Bowling Session

Before recording the video footage of the bowlers to measure release speed, knee action and knee angle

a warm up was provided using the RAMP model (Jefferys, 2007). This included light plyometric drills

such as stride walkthrough, wall drives, stride & stick, A skips, backward skips and straight leg skips

19

Figure 7. Calibration of objects in background or foreground for release speed

Foreground

Background

followed by activation phase using ankle dorsi & planter flex, glute bridges, crab walks, scapula

protractors and scapula setting. Mobilisation drills such knee tucks, high kicks, leg swings backwards

and side to side, carioca, bodyweight squat, lunge, lunge with thoracic rotation, lunge with overhead

reach, hip drive and shoulder rotations were performed followed by short sprints and bowling practice.

Post warm up bowlers were provided with 5.5oz Shepherds and Neame Essex League issued cricket

balls and allowed to perform their own personal bowling procedure in order to gain their rhythm and

accuracy. Bowlers were required to pitch the ball at good length on a line between the stumps and

return crease. Bowlers were allowed a maximum of four deliveries for the data collection and the

average speed and knee angles were used for the data analysis.

Strength Assessments

Isoinertial strength assessments were selected to measure the concentric & eccentric strength, and

stretch shortening cycle qualities of the participants. Studies performing isoinertial strength tests have

identified a moderate to strong correlation with dynamic movements (Cronin & Hansen, 2005) and due

to its close correspondence with sporting movements including closed kinetic chain assessments

remains a favourable choice over other types of strength assessments (Meylan, Cronin & Nosaka,

2008) as highlighted in Table 8.

Table 8. Comparison of strength assessmentsAssessment Advantages Disadvantages Correlation with

Athletic Performance

Isometric (Constant tension through ROM)

Reproducible, eliminates technique

Expensive to run, often single joint

Low to moderate correlation

Isokinetic (Constant Peak torques at various Open chain Low to moderate

20

velocity through ROM)

constant velocities, eliminate technique, highly reproducible

assessment, constant velocity, expensive to run

correlation

Isoinertial (Constant gravitational load)

Closed kinetic chain, multi-articular, variable velocities, easy to implement

Reliability, technique Moderate to high correlation

Concentric capacity was measured by vertical jump tests such as the counter movement jump (CMJ)

and the squat jump (SJ) as they are the most utilised assessments of concentric performance of leg

extensors (Baker & Nance, 1999; Wisloff et al., 2004; Stone et al., 2003) and produce high reliability

as compared to other vertical jumps such as the sergeant jump and abalakow jump (Markovic, Dizdar,

Jukic, & Cardinale, 2004). Eccentric strength was measured by obtaining the 1 RM of each participant

by progressively loading the barbell on a modified smith machine and performing a bi-lateral squat

movement pattern (Murphy & Wilson, 1997). The stretch shortening cycle (SSC) was quantified by the

reactive strength index (RSI) which is the most commonly used method by performing depth jumps via

the use of a drop box (Flanagan & Harrison, 2007). The vertical jumps and the RSI were measured

using an electronic switch mat (ESM) developed by FLS Jump Mat, Tyrone, Ireland which could

measure jump height in millimetres and flight and ground contact time to 0.001 secs.

Prior to the strength assessment, the participants went through a warm up. This included a raise,

mobilize, activate and potentiate phase according to Jefferys (2007) model. This involved a 5 min static

cycling, ankle dorsi & planter flex, good mornings, high kicks, leg swings backwards and side to side,

bodyweight squats, walking lunges, lunges with overhead reach, jumps in place, and single leg jumps.

The strength test took place in order RSI, CMJ, SJ and 1 RM of eccentric strength according guidelines

by Tanner & Gore (2013) and Baechle & Earle (2008), where more explosive and power movements

along with multi-joint movements should precede aerobic and isolated joint type of movements. A 5

21

min rest was provided during the transition to each strength test and four practice and four trial jumps

were performed for the RSI, CMJ and SJ. The greatest result for each trial for each participant was used

during the analysis. The RSI, CMJ and SJ were performed without any arms swings according to

guidelines by Bosco et al., (1995) as the arm swings may act as a confounding variable in producing

greater jump heights, peak power production and take off velocity whilst measuring the knee extensor

concentric and stretch shortening cycle ability, and hence hands were kept on the hips during these

vertical jump tests.

For the RSI measurement, participants were asked to perform a depth jump using a drop box of 33 cm

which is a standard depth used in most studies (Kenny et al., 2012; Flanagan et al., 2008) and landing

on the ESM half a metre in front of the drop box. Participants dropped off with both feet, without

stepping down or jumping up, landing with toes facing downwards, with ankles, knees and hips all in

one line. Countermovement was reduced by stiffening the lower limbs and exploding off the jump mat

immediately after making contact and reducing the ground contact time. Jump height was maximized

and legs kept straight during the flight time with participants finally landing with toes pointing down in

the same position at take off. A minutes rest was provided during each jump (Read & Cisar, 2003).

For the CMJ and SJ participants stood on the jump mat with feet shoulder width apart with hands on

hips with knees and hips fully extended. They were then asked to squat until hips crease was in line

with knees or thighs were parallel to the floor. In case of SJ this position was held for 3 seconds,

however in case of CMJ, participants instantly jumped explosively and forcefully causing the hips,

knees and ankles to extend. Participants landed with both feet on the mat with straight knees, toes

pointing downwards, however cushioning the landing by flexing at ankles, knees and hips. A rest

period of 2-3 minutes was provided during the jumps. The difference between a SJ and CMJ is the

contribution of the SSC towards the maximal power production phase during concentric phase. During

22

a SJ a 3 sec isometric hold is observed before the concentric phase of the jump is executed, known as

the amortization phase, which is sufficient time to dissipate the energy stored due to the SSC (Wilson

& Pryor, 1994). Whereas during the CMJ the amortization phase is kept <0.3secs in order to use the

energy stored more efficiently (Schmidtbleicher, 1992).

Eccentric strength was measured by measuring the 1 RM of each participant and calculating the value

as the participants percentage body weight (% BW). Using a modified smith machine the barbell was

placed across the upper trapezius and rear deltoids, with hands firmly gripping the barbell as close to

shoulders as comfortably. In an upright position and feet shoulder width apart, participants descended

till the hip crease was in line with the knees using a tempo of 3 secs (Schoenfeldn, 2010), whilst

maintaining a neutral spine. During the descent heels were not allowed to lift off the floor and knees

were allowed to travel beyond the ankles however in line at all times. Metal stops were used on the

smith machine to prevent the participants from going past hips breaking parallel. 1 RM was assessed by

performing 3-5 attempts, with a rest period of between 3-5mins between the eccentric phases of the

squat (Newton et al., 2011).

Statistical Methods

Summary statistics of the measured variables were presented as the mean and standard deviation. The

correlation (r) between variables was calculated using the Pearson’s product-moment correlation. To

determine whether these correlations were statistically significant, critical values were calculated using

two-tailed test of significance via t-distribution tables with α = 0.05. A backward stepwise multiple

linear regression analysis was performed to predict the best performance variables in a model for the

release speed of the ball with α = 0.05. The strength of the relationship was characterised by r, whereas

the meaningfulness of r was measured by r2 by measuring the variance of the release speed of the ball

caused by the performance variables. In order to establish whether there was any significant difference

23

between the groups in the release speeds and strength measurements, independent t-tests were

performed using a two-tailed test of significance using standardised tables from the t-distribution where

the critical values were calculated at α=0.05.

24

RESULTS

The means and standard deviations of the performance variables measured of the 20 participants in the

study are summarised in Table 9.

Table 9.Mean and Standard Deviation of Performance Variables (where n=20)Performance Variable Mean Standard DeviationRelease speed (m/s) 29.2 1.4

Knee Angle (°) 140.8 19.0RSI 1.132 0.170

CMJ (mm) 293 42SJ (mm) 269 39

(Bowler data available in Appendix E)

The correlation coefficients for the individual mean performance variables with mean release speed are

given in Table 10. 1 RM (% BW) and RSI showed a moderate correlation with the release speed of the

ball. However 1 RM (% BW) was the only performance variable which showed a significant

correlation with the release speed of the ball (t = 2.25, p<0.05).

Table 10. Correlation Coefficient (r) for Release Speed vs. Performance Variables (n=20)Correlation Variables Correlation Coefficient (r) Significant Correlation

vs. 1 RM (% BW) 0.47 Yesvs. RSI 0.32 Novs. CMJ 0.23 Novs. SJ 0.14 No

vs. Knee Angle 0.03 NoNote: Above have been sorted highest to lowest in terms of correlation strength

Despite only one variable significantly correlating with the release speed of the ball a backward

stepwise multiple linear regression was performed in order to capture any correlation amongst the

performance variables, known as multicollinearility, thus allowing more than one variable to be

included in the regression model to a significance level of α = 0.05. The regression model still reduced

the performance variables to 1 RM (% BW) which correlated significantly with release speed of the

ball (r = 0.47, t= 2.46, p = 0.04) shown in Figure 8. This models describes that 22% of the variance in

25

the release speed of the ball observed between the bowlers can be explained by the 1RM (% BW) of

the participants.

1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.620

22

24

26

28

30

32

34

R² = 0.218943097688785

1 RM (% Body Weight)

Rele

ase

Spee

d (m

/s)

Figure 8. Significant correlation between 1 RM (% BW) and release speed of the ball

As no correlation was found between the knee angle and the release speed of the ball in the complete

sample of bowlers (r = 0.03), correlation coefficients of average knee angle against average release

speed of the ball were produced within groups of the varying knee actions. None of the groups showed

any significant correlation of knee angle with the release speed of the ball despite showing moderate to

strong correlations. A breakdown of the total number of bowlers into their respective knee actions is

shown in Table 11 with Figures 9, 10 & 11 plotting average release speeds against average knee angles

for Group A, B & C respectively.

Table 11. Knee action type and number of participants in each groupGroup Type of knee action No. of bowlers

A Straight Leg 3B Flexed Knee 12C Knee flexes and then extends 5

26

150 155 160 165 170 17527.5

28

28.5

29

29.5

30

30.5

R² = 0.975786188467452

Avg .Knee Angle (degrees)

Avg.

Rele

ase

Spee

d (m

/s)

Figure 9. Group A release speed vs. knee angle (r=0.98, t=6.34, α=0.05)

115 120 125 130 135 14020

22

24

26

28

30

32

34

R² = 0.108017296752959

Avg. Knee Angle (degrees)

Avg.

Rel

ease

Spe

ed (m

/s)

Figure 10. Group B release speed vs. knee angle (r=-0.33, t=-1.10, α= 0.05)

27

156 158 160 162 164 166 168 170 172 17427

27.5

28

28.5

29

29.5

30

30.5

31

31.5

32

R² = 0.0503184728642324

Avg. Knee Angle (degrees)

Avg.

Rel

ease

Spe

ed (m

/s)

Figure 11.Group C release speed vs. knee angle(r = -0.22, t = -0.39, α = 0.05)

Though there was a difference in the average release speed of the ball between the groups shown in

Figure 12, these differences were not significantly different according to the independent t-tests. The

group where the knee flexed and then extended had the greatest release speed (29.4 ± 0.8 m/s) followed

by Group A which had a straight knee action (29.2 ± 0.8 m/s), and Group B, a flexed knee action,

reported the slowest average release speed of the ball (29.1 ± 1.8 m/s).

A (Straight Knee) B (Flexed Knee) C (Knee flexes then straightens)

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

Knee Action

Ball

Rele

ase

Spee

d (m

/s)

Figure 12. Comparison of release speed of the ball between groups

28

For the strength measurements, no significant difference in the measurements was observed between

the groups in all the measured variables apart from the RSI. Though Group A reported a higher mean

RSI value (1.216 ± 0.042) than Group B (1.056 ± 0.153), these were not significantly different.

However Group C reported a significantly higher mean RSI value (1.264 ± 0.167) when compared to

Group B as shown in Figure 13. For the CMJ mean values Group A and Group B reported similar jump

height values of 298 mm whereas Group C had an average value of 276.8 mm, with no significant

difference between the groups as illustrated in Figure 14. Group B had the greatest mean SJ height

value (276 ± 46 mm) followed by Group A (265 ± 31 mm) with Group C having the least SJ height

value (254 ± 25 mm). Neither of the groups had any significant difference as shown in Figure 15. For

the 1 RM (% BW) Group C had the highest value (1.89 ± 0.27 %) followed by Group B (1.82 ± 0.29

%), with Group A having the lowest 1 RM value (1.77 ± 0.15 %) with no statistical difference in the

mean values between the groups as shown in Figure 16.


0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

*

*

Knee Action

RSI

Figure 13. *Significant difference in mean RSI between Group B and C (t = -2.50, p<0.05)

29


265

270

275

280

285

290

295

300

Knee Action

CMJ (

mm

)

Figure 14. Comparison of mean values of CMJ between groups


240

245

250

255

260

265

270

275

280

Knee Action

SJ (m

m)

Figure 15. Comparison of mean values of SJ between groups

30


1.7

1.75

1.8

1.85

1.9

1.95

Knee Action

1 RM

Bod

y W

eigh

t (%

)

Figure 16. Comparison of mean values of 1RM (% BW) between Groups

31

DISCUSSION

The results indicate that within this sample of bowlers, the knee angle at FFC had no significant

correlation with the release speed of the ball. This was also true for the within group knee angle

correlations with the release speed of the ball for the varying knee actions, as moderate to strong

correlations were found however with no statistical significance. As such within this sample of bowlers

the knee angle cannot be used as a single predictor variable for the release speed of the ball or even

within a multivariable model as the multiple regression analysis did not achieve statistical significance

with the knee angle as a variable within the model. Though there were differences in the mean release

speeds of the ball for the varying types of knee actions these were not statistically significant and can

be associated with experimental errors in the studies. There was no significant difference in the

eccentric capacity, as recorded by 1 RM (%BW), between the varying knee actions thus rejecting the

hypothesis that a more extended knee possessed more eccentric ability. This is also supported by the

result that a straighter knee group had a lower mean 1 RM (% BW) score than the flexed knee. The

flexed knee action reported the highest mean CMJ and SJ heights, though these were not statistically

significant the findings contradict the hypothesis that a knee action which flexes and then extends

should possess a greater concentric capacity of the knee musculature. Though there is limited literature

available on fast bowlers utilising the stretch shortening cycle in generating greater power in the release

speed of the ball, interestingly RSI of bowlers who flexed and then extended at front foot contact had a

significantly greater mean value than the flexed knee action. This indicates that the stretch shortening

cycle maybe a bio-motor quality within this type of knee action used for power production. During this

study the 1 RM (% BW) was the only variable which could be classified as a predictor variable in the

release speed of the ball, suggesting that within this sample of bowlers increased strength had a greater

32

role to play than other variables such as knee angle, action or concentric capacity of the knee

musculature.

No correlation was observed between the knee angle and the release speed of the ball (r = 0.03,

p<0.05). This is contrary to other studies, summarised in Table 12, which have reported a moderate to

strong relationship between a more extended knee angle at front foot contact and the release speed of

the ball.

Table 12. Studies investigating correlation of knee angle with release speed of the ballAuthor r value P value

Wormgoor et al. (2008) r = +0.52 P = 0.005Portus et al. (2004) r = + 0.37 P = 0.02

Burden & Bartlett. (1990) r = +0.41 P = 0.02Loram et al. (2005) r = +0.71 P = 0.011

The variation in the strength of the correlation can be associated with the differences in the studies in

terms of selection of bowlers with Burden et al. (1990) selecting international bowlers for their studies,

whereas the other studies have taken bowlers from college, club and first class level. In particular

whereas other studies have recorded average knee angles and release speeds of the ball by providing a

number of deliveries, Portus et al. (2004) recorded only one delivery per bowler in the sample. The

frame rates used have also varied from 50 Hz to 250 Hz. The release speed of the ball has been being

measured via a radar gun or video imaging. Similarly the knee angle has been measured either by

placing markers, manual tracking or auto tracking using biomechanical software in two dimensions.

Experimental errors also exist due to the true joint angle may not have been measured in exactly the

same plane perpendicular to where the camera was placed (Bartlett et al., 1996). However in a study

conducted by Portus et al. (2000), a moderate but insignificant correlation (r = 0.52) between knee

angle and release speed was reported in a sample of 14 club cricketers. The study also showed that a

more flexed knee at front foot contact was significantly negatively correlated to the trunk stability tests

33

performed (r = -0.64, p=0.01). The trunk is defined as the lumbo-pelvic region which is required to

provide a stable foundation for the movement of upper and lower limbs and in transmitting forces

(Kibler, Press & Sciascia, 2006) and thus it has been proposed by Portus et al (2000) that bowlers who

land with a more flexed knee develop the trunk musculature for stability more so than bowlers with a

straighter knee transferring forces more efficiently in a closed kinetic chain by allowing the trunk to act

as a rigid lever as opposed to the front limb in order to increase the release speed of the ball. Thus it is

possible that trunk stability is a factor in increasing the release speed of the ball amongst club fast

bowlers who do not extend their knee and hence compensate for the lack knee extension.

Though previous studies have identified a significant relationship between the knee angle and release

speed of the ball, they have failed to provide a rationale as to the cause of the knee action and its

relationship with the release speed of the ball. In the current study no significant relationship was

established between the strength qualities of the lower limb and its relationship with the knee action

thus rejecting previous theories that a straighter knee possesses more eccentric ability whereas a knee

that extends upon front foot contact possesses a greater concentric ability. These results may indicate

that the knee action amongst fast bowlers is potentially a function of skill and not motor abilities such

as strength (Schmidt & Wrisberg, 2000). If this was a valid finding it may be possible that an increase

in release speed of the ball is also a factor of the radial distance between the lever arm i.e. front foot

and the bowling arm at the point of release (Elliot et al, 1986). In which case a more extended knee

would increase the height of the release position of the arm, which in turn would increase the tangential

velocity of the ball according to the equation V= rω (where ω is the angular velocity). As this

relationship is mechanically credible, studies into anthropometric measurements of fast bowlers and the

relationship with the release speed of the ball may provide an insight into whether this relationship is

true or not, as greater anthropometric measurements should correlate with the release speed of the ball.

According to Glazier, Paradisis and Cooper (2000), a significantly moderate correlation was found

34

between the upper body limb lengths and release speed of the ball such as the total arm length (r = 0.58,

p < 0.05), shoulder wrist length (r = 0.62, p < 0.05) and right humerus (r = 0.36, p<0.05) amongst nine

collegiate fast bowlers. A study by Pyne et al. (2006) showed a significant difference (p<0.05) in the

peak and mean release speed of the ball between first class senior and junior bowlers (VPeak 35.2 vs.

27.7 m/s, Vmean 34.2 vs. 26.6 m/s). It was observed that though arm and leg length were contributing

factors to the difference in the release speed of the ball between the groups, the magnitude of the

difference was only moderately larger in senior players and differences in upper and lower limb

strength, body mass and muscle composition were larger in magnitude. However when multiple linear

regression analysis was performed by selecting anthropometric and strength variables within junior and

senior bowling groups, arm length was a variable that was only significant within the senior bowlers

amongst other variables as the predictor for release speed. Table 13 shows the variables that were

shown to be the best predictors of release speed in the groups according to Pyne et al. (2006).

Table 13. Anthropometric and strength predictors amongst junior and senior bowlersGroup Variables Multiple r Multiple r2

Junior Static jump, bench throw, CMJ, body mass

0.86 0.74

Senior Deltoid throw, static jump, CMJ, arm length, A-P chest depth

0.74 0.54

Study taken by Pyne et al. (2006)

It appears that within bowlers at a junior skill level, anthropometric measurements such as arm length

and leg length do no significantly contribute to the release speed. With these results in mind it is

possible that a greater knee angle at front foot contact would have no significant impact on the release

speed of the ball due to a greater release height of the ball contrary to the theory proposed by Elliot et

al. (1986). The current study showed no correlation (r = 0.03) between the knee angle and release speed

of the ball, and though no method was established to measure the differences in release height of the

35

ball and the amount of knee extension in the current and previous studies, there are indications from

previous literature that release height of the ball does not significantly impact the release speed of the

ball amongst junior and club bowlers (Wormgoor et al., 2010; Loram et al., 2005). This relationship of

knee angle and release speed of the ball due to greater release height of the ball may only be significant

amongst senior high performance bowlers (Wormgoor et al., 2008; Portus et al., 2004; Burden &

Bartlett.,1990) which play a part post growth and maturation, as according to Pyne et al. (2004) the

difference in release speeds of the ball between junior and senior bowlers was due to contributing

factors of muscle and body mass, and concentric measurements of strength of the upper and lower

body. These results may be supported by the current study where 1 RM (% BW) was the only variable

which had a moderate and significant relationship with the release speed of the ball explaining 22% of

the variance in the release speed of the ball amongst the sample set of club bowlers. Though this

strength assessment was a measure of the lower limb eccentric ability, significantly moderate to strong

correlations have been reported between concentric and eccentric modes of knee flexor and extensor

muscle groups (Wu, Li, Maffulli, Chan & Chan, 1997). Strength development is also a pre-requisite

and major contributor to power generation (Stone et al., 2003; Paavolainen, 1999) and is a fundamental

pillar upon which other bio-motor abilities such as speed can be expanded upon (Kraemer & Szivak,

2012). There seems to be evidence to support that amongst junior fast bowlers strength and physical

maturation plays more of a critical role in increasing the release speed of the ball than extension of the

knee at the front foot contact. A study by Ranson et al. (2009) showed that contrary to the coaching

interventions to extend the knee at front foot contact, a less straight knee was observed i.e. increased

knee flexion, amongst junior fast bowlers after a two year period. Despite the reduction in knee

extension, the bowlers still increased the release speed of the ball by a mean of 1.4 m/s. Though the

coaching interventions used are questionable, as no details have been provided on the types of feedback

mechanisms used which is key to skill acquisition (Liu & Wrisberg, 1997; Guadagnoli & Kohl, 2001),

36

the increase in release speed of the ball was proposed to be due to the physical maturation of the

bowlers over the two years.

According to the knee actions prescribed by Bartlett et al. (1996), a difference in release speeds of the

ball was observed in the current study however these were not significantly different between the

different knee actions. These results support the findings of Portus et al. (2004) and Portus et al. (2000)

who recorded a difference in the mean release speed of the ball between the groups with no significant

difference. Both studies also reported that the knee action which flexed and then extended produced the

greatest mean release speed, and the knee action which was more extended at front foot contact also

recorded a greater release speed than the flexed knee action. However both studies also used different

criteria than Bartlett et al (1996) in order to classify the knee action and grouped the knee actions based

on within sample movement patterns with no reference to other studies. Table 14 summarises the knee

actions and release speeds of the studies mentioned and compares it to the current study.

Table 14. Comparison of current study with previous studies on knee action and release speedsStudy Types of knee actions Respective release speeds

Current Straight, flexed, flexes then extends

29.2 ± 0.8; 29.1 ± 1.8; 29.4 ± 0.8

Portus et al. (2000) Knee angle >177°,148-171°; 123-139°

32.4 ± 0.7; 32.1 ± 1.5; 31.3 ± 1.5

Portus et al. (2004) Flexor-extender; extender; braced; flexed

35.6 ± 1.3; 35.4 ± 2.3; 33.9 ± 2.5; 33.8 ± 1.8

According to previous literature the knee action which is able to extend after the point of front foot

contact and before the release speed of the ball, should possess a more concentric ability of the knee

musculature (Wormgoor et al., 2010). This hypothesis has been rejected in the current study as the knee

action that extended did not measure greater concentric capacity as assessed by CMJ and SJ heights.

The flexed knee action had greater jump heights in the CMJ and SJ than bowlers who extended their

knees, though the mean values were not significantly different. Most studies into kinematic analysis of

fast bowlers have been taken during the delivery stride (Bartlett et al., 1996) and thus performance

37

measurements such as release speed of the ball and strength measurements are assessed relative to this

isolated discrete moment in time and studies fail to address technique factors that underpin these

performance measurements in the entirety of a bowling action from run up to follow through (Glazier

& Wheat, 2014; Lees, 2002). This maybe the case with the bowlers who have a flexed knee (<150°) at

point of release, however extend their knee during the follow through for a more upright position which

has been observed in this sample of bowlers, though no formal knee angles and time to extension have

been calculated. It may be possible that bowlers with a flexed knee action develop more concentric

ability of the knee musculature as assessed by CMJ and SJ, as they go through a greater range of knee

extension whilst overcoming vertical forces ranging from 4-9 times the body weight (Hurrion et al,

2000; Elliot et al, 1986; Foster et al, 1989; Portus et al, 2004) as compared to straight knee actions

which overcome the same forces within a smaller range of knee extension. Thus CMJ and SJ may be

assessments of concentric ability, more specific to bowlers with a flexed knee action during the follow

through. Due to the possible effect of the principle of dynamic correspondence (Siff & Verkhoshansky,

2006) between CMJ and SJ and the follow through of flexed knee actions, these bowlers may develop

more concentric capacity of the knee musculature. Interestingly the efficacy of the CMJ test has been

questioned by Pyne et al. (2004) for fast bowlers as the study reported a negative correlation between

the release speed of the ball and the CMJ, though the testing protocol was different using a modified

smith machine to assess single leg concentric capacity with errors due to execution of technique, and

hence did not recommend the use of single legged CMJ assessment in future studies.

The rationale as to the movement pattern of knee actions during fast bowling have predominantly been

proposed by bio-motor abilities of either having high eccentric strength of the knee musculature for a

straight knee action (Portus et al., 2004) or having a high concentric capacity for a knee action that

extends after front foot contact (Wormgoor et al., 2010). Very little consideration has been given to the

knee action which flexes and then extends after front foot contact, effectively utilising the stretch

38

shortening cycle in order maximise the power production in the release speed of the ball by increasing

the joint centre speeds sequentially from proximal to distal segments of the body. This may partly be

because this type of knee action is very rare amongst fast bowlers according to a review by Bartlett et

al. (1996). However similar movement patterns have been observed in javelin throwers, which exhibit

the same generic movement patterns from run up to release of the javelin as fast bowlers (Bartlett et al.

1996; Komi & Mero, 1985). The knee action where the joint flexes and then extends has been observed

amongst javelin throwers (Komi et al., 1985; Mero et al., 1991), and the stretch shortening cycle may

be a contributor to the peak joint centre speeds in the proximal to distal firing pattern in such a knee

action (Mero et al., 1994) though an increase in joint centres is observed in most throwing activities

irrespective of type of action (Whiting, Gregor & Halushka, 1991). Whilst no studies have quantified

the efficacy of the stretch shortening cycle in this type of knee action, the results of the current study

showed that there is a significant difference in the RSI scores between a flexed knee and one which

extends. Thus bowlers who flex and then extend their knees may potentially utilise the stretch

shortening cycle more efficiently causing an increase in the work output from the knee musculature

(Portus et al., 2004) which may be a contributor to the increase in release speed of the ball, though a

significant difference in the release speed was not observed in the other knee actions.

In the current study, the bowlers had release speeds in the range of 26.7 to 32.5 m/s (mean 29.2 ± 1.4

m/s). According to the classification of bowlers by release speed, this sample of bowlers can be

classified as medium-fast bowlers and places the bowlers towards the medium end of the spectrum of

the medium-fast category (Abernethy, 1981). Table 15 shows the classification of bowlers according to

release speed.

Table 15. Classification of bowlers according to release speedClassification Release speed (m/s)

Slow – medium 18 - 27Medium – fast 27 - 36

Fast 36 – 40.5

39

Express > 40.5

Though the study aimed at specifically targeting fast bowlers the sample set was formed of medium

paced bowlers as pre determining and selecting bowlers based on their classification could not be

performed due to time constraints. However a contributing factor to the medium pace of the bowlers

maybe explained by the short run up that was provided during the bowling analysis within the indoor

setting, though this was not scientifically evident. During the analysis bowlers were provided with a

run up length of 12 meters due to the dimensions of the sports hall, whereas most studies into the

biomechanical analysis and measurements of release speed of the ball have provided a full run up at

club and elite level (Hurrion, Dyson & Hale, 2000; Worthington et al., 2013). Though these studies

have not specifically provided the exact dimension of the run up length it may be assumed that this run

up length was up to 30 m as Hurrion et al (2000) conducted the study outdoors and Worthington et al.

(2013) conducted studies in facilities sponsored by the English Cricket Board (ECB). Although run up

length has not statistically been reported as having a direct and significant relationship with the release

speed of the ball, it is considered a contributing factor to the run up speed of the bowlers which has

been reported to significantly impact the release speed of the ball summarised in Table 16.

Table 16. Relationship between run up speed and release speed of the ballStudy Correlation MeasurementGlazier et al. (2000) r = 0.73 (p<0.05) Taken at back foot strikeFerdinands et al. (2010) r = 0.58 (p<0.001) Taken at back foot strikeBurden et all. (1990) r = 0.21 (p<0.05) Taken at release of ballWorthington et al.(2009) r = 0.45 (p<0.001) Taken at back foot strike

A study on run up speeds by Mason, Weissensteiner & Spence (1989) showed that run up speed

increased when the run up length was increased amongst 15 medium-fast bowlers. Run up speed was

recorded at 6.1 m/s, 5.7 m/s and 5.1 m/s for run up lengths of 8-16 m, 4-8 m and 0-4 m respectively.

The study did not report any release speeds of the ball however reported the mean speed of the all the

trials at 32.4 m/s. A study by David and Blanksby (1976) also showed that bowlers with a longer run

40

up were faster than the slower bowlers by a mean release speed of 4.7 m/s, though the run up lengths

were not reported. Though the relationship between run up length and release speed of the ball has not

been investigated thoroughly, as most studies have been more focused with the run up speed (Glazier &

Worthington, 2014), the results of the current study may have been obscured by placing constraints on

the bowlers via the run up length and reducing the run up speed and rhythm within the indoor setting

(Hurrion et al., 1997). In order to maximise release speed of the ball Elliot and Foster (1986) have

prescribed a run up length between 15 m and 30 m.

During the filming of bowlers, experimental errors existed in measuring the release speed of ball within

the bowling crease. Though this was minimized by bowlers aiming to pitch the ball on a line in

between the stumps and return crease, errors exist in two dimensional analysis because of the angle at

which the ball is released due to the shoulder and hip rotation at the delivery stride (Bartlett et al.,

1996) causing movement of the bowling arm in the transverse plane. Due to the various types of

bowling action errors in measuring the release speed of the ball in two dimensions will always be

inherent, however can be minimized via the use of a radar gun. Similarly errors existed in measuring

the amount of knee extension via a protractor by identifying features the joint centres of the ankle, knee

and hip. Previous studies have used markers (Worthington et al., 2013a; Ranson et al., 2009) to identify

joint centres to measure the knee angle. According to Segal et al. (2013) the knee angle should be

measured from the knee centre of rotation forming a line to the lateral malleolus at the ankle and to the

greater trochanter at the hip. However without the aid of markers specifically placed at these joints,

inaccuracies existed in identifying these features due to the limited resolution of the video images. Further

errors existed in measuring the joint angle as the knee actions may not have been recorded in exac tly the

same plane perpendicular to the camera due to bowlers positioning their front foot at various positions

at the popping crease.

41

The results and literature review of this study indicate that amongst club level fast bowlers, the knee

angle and type of knee action does not significantly impact the release speed of the ball and strength

plays a greater role as a predictor variable for the release speed of the ball. However at a senior level

where bowlers have developed physical maturation and a solid foundation of bowling with the correct

technique, knee angle and actions may become contributors to the release speed of the ball as it

increases the tangential velocity of the ball due to an increased release height. It also appears that the

type of knee action is not dependent or related to the strength of the lower limb and rather is a function

of skill and technique. Strength or bio-motor ability of the knee musculature is not necessarily related

to the type of knee action at the delivery stride but could correspond to other dominant stages in a

bowling action. For the Strength & Conditioning coach the results indicate that amongst junior and club

level bowlers strength development should be an area of focus along with a safe bowling technique in

order to increase the release speed of the ball. However amongst skilled senior bowlers a goal to

increase the knee angle at front foot contact maybe considered via the use of feedback coaching

interventions, in order to increase the release speed of the ball. Future studies should include

homogenous sample of bowlers in order to remove covariate influence of skill level on performance

measurements such as release speed and investigate the strength and knee actions relationship. Studies

should be performed further at junior, senior, first class and international level independently to

understand at what level of skill knee actions influence release speed of the ball. Similarly as strength

was identified as a predictor variable, strength programs should be provided and tracked via isoinertial

assessment within a sample of bowlers to identify a threshold at which strength gains no longer

improve the release speed of the ball and knee actions possibly do.

42

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APPENDIX A: DOMESTIC & INTERNATIONAL PLAYER WORKLOAD AND INJURY

RATE

ACB report on player matches available from 1996 to 2002Team 1996 1997 1998 1999 2000 2001 2002Australia 414 1218 1020 1327 1108 1153 748New South Wales 416 464 468 510 504 566 664Queensland 357 396 396 350 399 494 566South Australia 306 330 459 465 387 413 530Tasmania 255 270 306 303 308 475 566Victoria 405 432 416 455 363 523 556Western Australia 342 396 414 367 449 570 587Total 2495 3506 3479 3777 3518 4194 4217% Δ YoY 41% -1% 9% -7% 19% 1%Report taken from the ACB (Australian Cricket Board) Injury Report 2001-02

Sport Health Report on designated player hours of exposure in matches each seasonCompetition 1999 2000 2001 2002 2003 2004 2005 2006

Domestic One-day

1819 1732 2685 2685 2685 2685 2598 2598

First Class Domestic

8658 9048 8892 8892 8580 9438 9126 8892

One Day International

996 1472 953 909 1386 1386 1039 1559

Test Cricket 2067 2067 1287 2379 1248 2691 2262 3042Total 15539 16319 15818 16867 15902 18204 17030 18097

% Δ YoY 5% -3% 7% -6% 14% -6% 6%Report taken from Sports Medicine Australia(SMA)

ACB and Sports Medicine Australia report on injuries/10000 player hours

Report 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006ACB 18.4 14.4 20.8 26.2 23.6 21.4 24.2% Δ YoY

-22% 44% 26% -10% -9% 13%

SMA 37.7 34.9 29.7 37.7 31.7 37 27.3 25.1% Δ YoY

-7% -15% 27% -16% 17% -26% -8%

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APPENDIX B: PARTICIPANT INFORMATION SHEET

Participant Information SheetProject Title

Varying knee actions and strength predictors of ball release speed amongst fast bowlers in cricket

Summary of TestingFor this project you shall be asked to participate in 2 sessions as below:

1. Bowling session2. Gym session for familiarisation3. Gym session

For both sessions the following till take place:

1. 15minute warm up2. 10 minute potentiation3. 20minute testing session4. 15minute cool down

During the bowling session your bowling action shall be recorded via the use of high speed cameras and two 50Hz cameras. You will be required to bowl no more than 12 deliveries excluding warm up deliveries which is at your discretion on how many deliveries you would like.

During the gym session you will be required to perform the following test:

1. Back squats to measure eccentric ability of knee musculature2. 2 types of jump tests (Squat jump, Counter Movement Jump)3. Depth jump (Using a drop box and then jumping immediately after ground contact)

The gym session should take place within 2 weeks of the bowling session

Session 1: Bowling Session

You will be required to bowl in an indoor pitch at the stumps. You will aim to pitch the ball at good length on the pitch. This session will record your bowling action via the use of high speed cameras for the below purpose:

Measure your bowling speed Measure your knee angle

The following protocol will take place:

1. 15minute warm up (Led by an S&C Coach-running & stretching)2. 10 minute potentiation (You will be able to ball on the pitch till you feel comfortable for the

testing phase)

51

3. 20minute testing session (You will bowl 6 delivery’s at the stumps by pitching the ball at good length)

4. 15minute cool down (Led by an S&C Coach- lowering heart rate & stretching)

Equipment used for this session:

High Speed Cameras 5.5 ounce cricket ball Stumps

Any specific requirements for the participant: You will be required to wear shorts

Session 2 & 3: Gym Session

You will be required to attend a strength assessment session at the gym. The assessment will be focused around measuring the strength of the knee musculature. The following tests will be performed:

1. Back squats to measure eccentric ability of knee musculature2. Jump tests 1 : Squat Jump3. Jump tests 1 : Counter Movement Jump4. Depth jump (Using a drop box and then jumping immediately after ground contact)

The following protocol will take place:

1. 15minute warm up (Led by an S&C Coach-use of free weights & stretching)2. 10 minute potentiation (Familiarisation with testing) 3. 20minute testing session 4. 15minute cool down (Led by an S&C Coach- lowering heart rate & stretching)

The strength measurement will be conducted as below:

1. Back squats to measure eccentric ability of knee musculature: A smith machine shall be used for this test. You will be required to do a back squat on the smith machine with load of 200% of your body weight loaded on the barbell. You will then be asked to lower yourself with a 3 second tempo till the stops on the rack. Weight will be added/removed every 4mins as required to measure your strength

2. Jump Test 1: A jump mat will be used for this test. You will be required to get into squat position on the jump mat and then jump as high as possible and explosively as possible. You will be given 4 attempts

3. Jump Test 2: A jump mat will be used for this test. You will be required to a countermovement on the jump mat and then jump as high as possible and explosively as possible. You will be given 4 attempts

4. Depth jump: A drop box and a jump mat will be used for this test. You will be required to free fall off the drop box with hips, knees and ankle aligned and then jump off immediately at ground contact as explosively as possible with little bending of the knees, hips and ankles. You will be given 4 attempts

Note: Session 2 must take place within 2 weeks of Session 1

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APPENDIX C: INFORMED CONSENT FORM

Informed Consent Form

Name of participant: _________________________________

Project titleVarying knee actions and strength predictors of ball release speed amongst fast bowlers in cricket

Main investigator & contact details: Sajeel Chaudhry, School of Sport, Health and Applied Science, St Mary’s University, Waldegrave Road, Twickenham, London, TW1 4SX, Email:[email protected]

Members of Research Team: Sajeel Chaudhry (Main researcher), Dr. Neil Bezodis (Project Supervisor)

DeclarationBy signing below, you are agreeing that:

1. You have read and understood the Participant Information Sheet2. Questions about your participation in this study have been answered satisfactorily3. You are aware of the potential risks (if any)4. You are taking part in this research study voluntarily5. I understand that I am free to withdraw from the research at any time without prejudice6. I have been informed that the confidentiality of the information I provide will be safeguarded7. I am free to ask any questions at any time before and during the study8. I have been provided with a copy of this form and the Participant Information Sheet

Data Protection: I agree to the University College processing personal data which I have supplied. I agree to the processing of such data for any purposes connected with the Research Project as outlined to me.Name of Participant ________________ Signed ________________ Date ________Name of Witness ________________ Signed ________________ Date ________--------------------------------------------------------------------------------------------------------------

If you wish to withdraw from the research, please complete the form below and return to the main investigator named above.

Project Title

Varying knee actions and strength predictors of ball release speed amongst fast bowlers in cricket

I WISH TO WITHDRAW FROM THIS STUDY

Name of Participant ________________ Signed ________________ Date ________

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Sajeel ChaudhrySchool of Sport, Health and Applied ScienceSt Mary’s UniversityWaldegrave RoadTwickenhamLondonTW1 4SX

APPENDIX D: PAR-Q

Physical Activities Readiness Questionnaire (PAR-Q)

Male ___

Name __________________________________

Address __________________________________

Postcode__________________________________

D.O.B __________________________________ Age:

Tel __________________________________

Email __________________________________

Height (cm)____________________ Weight (kg)__________________

1. Do you have a heart condition? Yes No

2. Do you feel pain in your chest when you exercise? Yes No

3. Do you have high blood pressure? Yes No

4. Have you had a heart attack or bypass operation? Yes No

5. Are you diabetic? Type 1: Yes No Type II: Yes No

6. Do you suffer from asthma or any respiratory conditions? Yes No

7. Do you have any bone or joint problems that could be made worse by a change in your physical activity? Yes No

8. Do you suffer from dizzy spells or fainting? Yes No

9. Do you smoke? Yes No (If Yes how many per day ________)

10. Have you had any operations in the last year? Yes No

11. Have you had any musculoskeletal injuries in the 6 months? Yes No(If Yes please provide details) _____________________________________________________________________________________________

54

Sajeel ChaudhrySchool of Sport, Health and Applied ScienceSt Mary’s UniversityWaldegrave RoadTwickenhamLondonTW1 4SX

_______________________________________________________________________________________________________________________________________________________________________________________

12. Do you drink? Yes No (If Yes how many units per week ________)

13. Have you suffered from any of the below: Details Stroke Yes No ________________________ Cancer Yes No ________________________ High Cholesterol Yes No ________________________ Epilepsy Yes No ________________________ Allergies Yes No ________________________

14. Do you suffer from any blood borne disease? Yes No

15. Are you taking any medications or supplements? Yes No(If Yes please provide details) _______________________________________________________________________________________________________________________________________________________________________________________________________________

16. Are there any other reasons that not prompted by the above that would prevent you from participating within the relevant activity? _______________________________________________________________________________________________________________________________________________________________________________________________________________

17. How many times a week do you exercise? ______________________________

Assessment Notes: _______________________________________________________________________________________________________________________________________________________________________________________________________________

_________________________________

Participant’s Name (Printed)

_________________________________ _________________________________

Participant’s signature Date

_________________________________

Test Co-ordinators Name (Printed)

_________________________________ _________________________________

Test Co-ordinators signature Date

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APPENDIX E: BOWLERS MEASUREMENTS FROM STUDY

Bowler ID

Knee Group

Average Bowling Speed (m/s)

Average Knee

Angle(°)Max RSI

Max CMJ

Max SJ1 RM (%

Body Weight)

001 A 28.50 151.5 1.242 266 235 1.73002 A 30.01 171.9 1.238 283 262 1.65003 A 29.11 156.8 1.168 345 297 1.94004 B 28.70 119.5 0.975 283 225 1.52005 B 32.49 128.3 1.060 320 277 1.90006 B 26.67 126.8 1.162 360 329 1.75007 B 28.54 131.0 1.040 240 232 1.76008 B 28.70 118.5 1.209 257 255 1.87009 B 30.46 121.9 1.091 247 229 1.76010 B 30.62 124.3 1.216 366 340 2.04011 B 26.82 135.8 0.796 258 263 1.57012 B 30.59 125.5 0.919 360 325 2.09013 B 27.15 130.0 0.974 289 289 1.69014 B 28.92 131.8 0.900 253 218 1.40015 B 29.97 124.9 1.324 343 328 2.48016 C 29.04 162.3 1.210 283 241 2.09017 C 28.99 157.0 1.312 301 270 1.75018 C 28.90 166.9 1.223 260 240 1.79019 C 29.37 172.9 1.060 249 229 1.60020 C 30.88 159.6 1.514 291 290 2.26

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Knee actions and strength predictors of ball release speed amongst fast bowlers in cricet