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Incremental training intensities increases loads on the lower back of elite female
rowers
Authors
Erica M. Buckeridge1,2 ,3, Anthony M.J. Bull2
, Alison H. McGregor1
1 Department of Surgery & Cancer, Imperial College London, UK
2 Department of Bioengineering, Imperial College London, UK
3 Human Performance Laboratory, University of Calgary, Canada
Corresponding Author:
Erica Buckeridge1,2 ,3
Human Performance Laboratory, Room B225
Faculty of Kinesiology, University of Calgary
Calgary, AB, Canada, T2N 1N4
Phone: +01(403) 220-3449
Abstract: 200 words
Main text: 3,997 words
Running Title: Lower back loads in elite rowers
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TITLE
Incremental training intensities increases loads on the lower back of elite female rowers
RUNNING TITLE
Lower back loads in elite rowers
KEY WORDS
Lower Extremity, Lumbosacral, Ergometer, Inverse Dynamics
ACKNOWLEDGEMENTS
The authors would like to acknowledge EPRSC and GB Rowing for their funding support, as
well as Robert Weinert-Aplin and Alex Wolf for their invaluable contributions and insights.
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ABSTRACT
Lumbar-pelvic kinematics change in response to increasing rowing stroke rates, but little is
known about the effect of incremental stroke rates on changes in joint kinetics and their
implications for injury. The purpose of this study was to quantify the effects of incremental
rowing intensities on lower limb and lumbar-pelvic kinetics. Twelve female rowers performed an
incremental test on a rowing ergometer. Kinematic data of rowers’ ankle, knee, hip and lumbar-
pelvic joints, as well as external forces at the handle, seat and foot-stretchers of the rowing
machine were recorded. Inter-segmental moments and forces were calculated using inverse
dynamics and were compared across stroke rates using repeated measures ANOVA. Rowers
exhibited increases in peak ankle and L5/S1 extensor moments, reductions in peak knee
moments and no change in peak hip moments, with respect to stroke rate. Large shear and
compressive forces were seen at L5/S1 and increased with stroke rate (p<0.05). This coincided
with increased levels of lumbar-pelvic flexion. High levels of lumbar-pelvic loading at higher
stroke rates have implications with respect to injury and indicated that technique was declining,
leading to increased lumbar-pelvic flexion. Such changes are not advantageous to performance
and can potentially increase the risk of developing injuries.
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INTRODUCTION
Rowers train at different intensities to develop aerobic fitness as well as leg power and strength.
When rowing at increasing intensities, negative changes in lumbar-pelvic kinematics and
reductions in range of motion (ROM) of the knee and hip have been noted (McGregor, Bull, &
Byng-Maddick, 2004; Murphy, 2009). However, little is known about the changes in joint
kinetics that occur with increasing rowing intensities. Such information would have relevance
towards understanding injury mechanisms and staging recovery to full time training following a
back or lower limb injury.
Few studies have estimated joint forces and moments during ergometer rowing. Halliday et al.
(2004) observed peak extensor moments about the ankle, knee and hip to be 100 Nm, 320 Nm
and 420 Nm respectively, in heavyweight male rowers. A bottom-up inverse dynamics approach
has been used to investigate differences in joint mechanics due to ergometer designs, to quantify
lower limb joint kinetics whilst rowing on fixed versus sliding ergometers (Greene, Sinclair,
Dickson, Colloud, & Smith, 2013). The fixed ergometer had higher peak moments and power
output at the knee, compared to the sliding ergometer. This was proposed to be due to greater
inertial forces that the rower must overcome at the start of the stroke. As such, kinetic modelling
of the rower can provide useful information pertaining to loads experienced by the rower, and
how these loads are influenced by various rowing conditions and indeed technique.
Commonly injured locations of the lumbar spine are the L4/L5 and L5/S1 joints and
intervertebral discs (Humphreys & Eck, 1999), which have been attributed to the large ROM and
compressive forces in this region. Deteriorations in posture, characterized by greater degrees of
lumbar-pelvic flexion, have been observed as stroke rate increased (McGregor, et al., 2004).
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This is thought to influence the magnitude of loads being transmitted through the lumbar-pelvic
region and may contribute to the development of chronic lower back injuries. It is particularly
important to investigate loading about the lumbar-pelvic joint as this is where the majority of
rowing injuries occur (Smoljanovic et al., 2009). However, only a limited number of inverse
dynamic models have been developed to quantify loading of the lumbar spine. The main
methods have used a bottom-up approach for the ankle, knee and hip, and a top-down approach
for the lumbar spine, where the trunk is a single segment connecting the shoulder to the pelvis
(Cerne, Kamnik, & Munih, 2011; Hase, Kaya, Zavatsky, & Halliday, 2004). A top-down
approach simplifies the trunk as a single segment, therefore the entire movement of the spine is
modelled as occurring about L5/S1 and may overestimate lumbar-pelvic forces and moments
(Kingma, deLooze, Toussaint, Klijnsma, & Bruijnen, 1996). No study has previously quantified
ankle, knee, hip and lumbar-pelvic loading during rowing using a bottom-up approach, where the
lumbar spine and pelvis are modelled as separate segments. Therefore, this study will employ a
bottom-up approach for modelling L5/S1 forces and moments through independent
measurements of both the pelvis and lumbar spine segments. Consequently, the aim of this study
was to develop an inverse dynamics model to examine the effects of incremental stroke rates on
lower limb and lumbar-pelvic joint kinetics and kinematics.
METHOD
Participants
Twelve elite heavyweight female rowers, all of whom rowed as part of the GB rowing squad in
the 2012 Summer Olympics participated in this study (mass 75.6±3.1 kg, age 28.1±2.7) at
Imperial College’s Biodynamics laboratory. Rowers with existing low back pain or any other
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serious injury were excluded. Imperial College Research Ethics Committee approved the study
protocol and informed consent was obtained from subjects.
Protocol
Following a 10 minute warm-up, participants performed a four stage ergometer step test. Each
step was 3 minutes in duration and was performed at the following stroke rates and split times:
18 strokes per minute at a split corresponding to 55% of race pace
24 strokes per minute (no split given)
28 strokes per minute (no split given)
Free rate i.e. an arbitrary stroke rate that corresponds to rowing a 500 m split at their
2000 m race pace (McGregor, Patankar, & Bull, 2008).
A minimum 5 minute rest period was permitted between each step.
Instrumentation
Rowers performed their trials on a modified rowing ergometer (Concept2 Inc., Morrisville,
Vermont, USA). On this ergometer force data could be captured from the handle (tensile force),
seat (vertical force) and bilaterally from the foot-stretchers (summed resultant force) (E. M.
Buckeridge, Bull, & Mcgregor, 2014; Murphy, Chee, Bull, & McGregor, 2010). Both the seat
and foot stretchers quantified the point of force applications. The flywheel was instrumented
with a linear encoder (ERN120, Heidenhain Ltd., Traunreut, Germany) for measurements of
stroke length. Kinematic data of the rowers were recorded using the electromagnetic Flock of
Birds (FOB) motion capture system (Ascension Technology, Burlington, USA). Six degree of
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freedom FOB sensors were attached to the rower at T12/L1 junction, L5/S1 junction, midway
along the lateral aspect of the thigh, and midway along the anterior aspect of the shank. These
sensors recorded 3D position and orientation of rowers’ lumbar spine, pelvis, right thigh and
right shank segments relative to an extended range transmitter. Three dimensional global
landmark co-ordinates of the right posterior-superior iliac spine, left posterior-superior iliac
spine, right anterior-superior iliac spine, left anterior-superior iliac spine, right lateral femoral
epicondyle, right medial femoral epicondyle, right lateral malleolus, right medial malleolus, right
5th metatarsal and right hip joint centre were derived through a digitisation procedure described
in Buckeridge et al. (in press). These digitised landmarks were used to construct local co-
ordinate systems of the pelvis, thigh, shank and foot.
Data Analysis
Data from FOB and load cells were acquired from separate data acquisition units, and were
software synchronised in a custom LabView program (Version 7.1, National Instruments,
Austin, Texas, USA) through simultaneous initiation of their data acquisition loops.
A three dimensional inter-segmental model was written in Matlab (Mathworks Inc., Natick, MA)
which represented the foot, shank, thigh and pelvis and lumbar spine as a rigid, five segment
system (Figure 1). In this model, the foot was treated as a single rigid segment. Linear and
angular Newtonian equations of motion were employed to calculate net moments about the
ankle, knee, hip and lumbar-pelvic joints (Winter, 1990). Anthropometric and segment inertial
properties were taken from Zatsiorsky et al. (1990).
Due to a limited number of FOB sensors it was only possible to perform a unilateral kinematic
analysis of the right lower limb, therefore distal moments at the pelvis were derived by assuming
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bilateral lower limb symmetry. Joint moments and forces from the right hip were doubled for
the sagittal plane and mirrored in the frontal and transverse planes, and seat force was included
as an additional force input in order to derive forces and moments at the pelvis. It was assumed
that seat force always acted through pelvis centre of mass.
All forces and moments were quantified in Newtons (N) and Newton meters (Nm) respectively.
To enable comparison of data between athletes these values were normalised to each rowers’
body mass. All data was time normalised as 0-100% based on handle force thresholds, where
0% is considered the catch position, and 100% representing the completion of the stroke prior to
the subsequent catch point. The middle ten strokes from each 3 minute trial were extracted for
statistical analysis, as they exhibited less variance than the first ten and the final ten strokes.
All kinetic and kinematic variables from Table 1 were extracted at the catch, point of maximum
handle force (MHF), finish and 10% recovery positions (i.e. 10% after finish position on the
scale of the whole stroke). These four time points give a good representation of the key
occurrences within a rowing stroke (E. Buckeridge, Hislop, Bull, & McGregor, 2012).
Maximum/minimum values within the drive phase were also extracted for kinetic variables,
whilst joint ROM in the sagittal plane was also calculated for each joint.
Statistical Analysis
All statistical analyses were performed using SPSS (version 19, IBM Corporation, New York,
USA). Means and standard deviations from ten strokes of each trial were computed, and
normality of the data set was tested using the Shapiro-Wilk test. A repeated measures ANOVA
was run with Step as the repeated measure. This test was employed to determine whether 3D
joint kinetics, kinematics, and associated performance measures changed according to stroke
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rate. Where an overall significance was seen, Bonferroni post-hoc tests were conducted to locate
differences. Significance level was set at p<0.05.
RESULTS
The performance results of the four stage step test can be seen in Table 2. A significant increase
in stroke rate and distance rowed, and a significant reduction in 500 m split time was seen across
the progressive stroke rates (p<0.001). Average stroke length appeared to decrease across
progressive stroke rates (Table 2). However, due to the large relative standard deviations, stroke
length did not demonstrate significant differences across stroke rates (p=0.713).
In terms of external forces applied to the rowing ergometer, peak and average forces recorded at
the handle and foot-stretchers remained constant across stroke rates. However, a significant
increase in peak seat force was observed with respect to stroke rate (p<0.05) (Figure 2). Peak
seat force occurred at 27.0±3.0% and 36.1±5.4% stroke cycle for rate 18 and free rate
respectively. A time normalised handle, seat and foot force curves for stroke rate 18 and free rate
can be seen in Figure 3, for a single representative subject.
Stroke rate had a large effect on inter-segmental forces and moments at the catch, finish and
recovery positions, and this was most notable for sagittal plane dynamics (Figure 4 and 5). With
respect to stroke rate, all joints exhibited significantly increasing extension moments at the catch
(p<0.05), and increasing flexion moments at the finish and during the recovery phase (p<0.05).
Compressive and shear forces increased with respect to stroke rate for all joints at the catch and
finish. This was with the exception of hip compression at the catch and L5/S1 shear force at the
finish, both of which were stable across all four stroke rates.
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Regarding non-sagittal plane joint dynamics, it was predominately values at the catch and finish
that were sensitive to stroke rate. In relation to peak values, only peak external hip rotation
moments and L5/S1 peak abduction moments increased with stroke rate. Additionally, values for
peak external hip rotation and peak L5/S1 abduction moments had some of the highest relative
out-of-plane moment values, at 11% and 13% of their respective joints’ peak extensor moment
values (Figure 4).
Regarding peak joint moments in the sagittal plane, ankle plantar-flexion moments increased
from 1.16±0.23 Nm/kg to 1.23±0.29 Nm/kg from Rate 18 to Free Rate (p<0.05). This occurred
alongside a 4.3° reduction in ankle ROM (Figure 6), which could be attributed to a less plantar-
flexed ankle at the finish position (p<0.05).
Peak knee extensor moments became significantly lower at progressively increasing stroke rates,
changing from 3.82±0.28 Nm/kg at Rate 18 to 3.68±0.29 Nm/kg at Free Rate (p<0.05). This
coincided with a progressively lower peak shear and peak compressive forces at the knee with
respect to stroke rate (p<0.05). Furthermore, there was a significant 6.3° reduction in knee ROM
(Figure 6, p<0.05), which was attributed to a 5.3° reduction in knee flexion at the catch and 2.3°
reduction in knee extension at the finish.
Peak hip extensor moments remained constant across stroke rates. There was a trend for reduced
hip ROM with respect to stroke rate (p=0.07) and a contributor to this would have been the 4.1°
reduction in hip flexion at the catch. Peak hip abduction moments significantly increased from
0.61±0.34 Nm/kg at Rate 18 to 0.71±0.45 Nm/kg at Free Rate (p<0.05). Additionally, hip
external rotation moments at the catch and finish significantly increased with respect to stroke
rate (p<0.05).
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Peak L5/S1 extension moments increased from 12.47±0.93 Nm/kg to 13.09±1.02 Nm/kg
(P<0.05). This was coupled by concurrent increases in peak L5/S1 compressive forces from
10.49±1.23 to 14.83±2.43 N/kg and peak L5/S1 shear forces from 11.91±1.69 to 12.25±1.89
N/kg. Furthermore, L5/S1 ROM increased from 15.61±5.21° to 18.23±5.13° (Figure 6), whilst
there was a 2.62° reduction in anterior rotation of the pelvis as stroke rate increased (p<0.05).
DISCUSSION
A bottom-up inverse dynamics model was developed to examine the effect of incremental
rowing intensities on joint kinetics of the lower limb and lumbar spine. To ensure that rowers
were performing at incremental intensities, ergometer results were compared across the four
stages of the test. Significant increases in stroke rate and distance rowed, and a significant
reduction in 500 m split times indicate that rowers were able to incrementally increase their
rowing intensity.
Biomechanical results revealed that forces and moments of the lower limbs and lumbar-pelvic
joint also changed with respect to stroke rate. With increasing stroke rate, there were concurrent
increases in peak ankle and peak L5/S1 extensor moments. However, reductions were seen in
peak knee extensor moments, whilst peak hip extensor moments were stable across rowing
intensities. According to figures 4 and 5 it is clear that mechanical demands of joints are
sensitive to stroke rate during the drive phase. This was particularly true for moments and forces
at L5/S1 which significantly increased with increasing stroke rates. Furthermore, a reduction in
peak knee extensor moments and no change in peak hip extensor moments across stroke rates
suggest that when stroke rate increases, there is reduced ROM from the lower limbs, which is
compensated for by increased ROM at the lower back. The changes in joint kinetics that were
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seen across progressive rowing intensities may occur as a result of changes in technique, where
increases in lumbar-pelvic flexion, as well as reductions in hip, knee and ankle ROM during the
drive phase may directly contribute to the changes in joint kinetics across rowing intensities.
These biomechanical changes can be compared to stoop lifting where there is a much greater
dynamic contribution from the lumbar spine and hip compared to the knees, whereas squat lifting
requires greater loading of the lower limbs (Hwang, Kim, & Kim, 2009). Kinematic changes
around the lumbar-pelvic region could be an important mechanism for the increased L5/S1
loading during ergometer rowing at free rate. Therefore, appropriately directed training to
improve technique during high intensity rowing, specifically movement quality of the lumbar-
pelvic region, has the potential to reduce compressive forces and extensor moments of the
lumbar-pelvic joint. However, the magnitude to which these loads could be reduced requires
further investigation.
The recovery phase was also sensitive to changes in inter-segmental forces and moments that
resulted from increasing stroke rates (Figure 4 and 5). All extensor moments significantly
increased in value at the catch position, and there were consistent increases in flexor moments
and tensile forces across all joints for the finish position and during the recovery phase. The
catch and finish positions mark the start and end of the recovery phase, so there are marked
dynamic differences in recovery as stroke rate increases. At rate 18 the rower slides naturally
back to the catch position exerting little effort, whereas higher stroke rates requires the rower to
progressively increase the speed of their recovery, thus generating negative work through greater
joint flexion moments. The dynamic differences between high and low rowing intensities have
previously been highlighted for on-water rowing. In 28 elite Canadian rowers, total kinetic
energy during the recovery phase was six times greater during high intensity rowing and
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approximately equal to the kinetic energy required during the drive phase (Bechard, Nolte,
Kedgley, & Jenkyn, 2009). As the results from this study also suggests, high intensity rowing
places greater demands on the body during the recovery phase, compared to rowing at a lower
intensity. These are important considerations when constructing training plans and analysing the
rowing stroke, where the importance of the non-propulsive phase should not be overlooked.
Whilst there were no significant differences across stroke rates in anterior shear forces at the
knee, Figure 5 shows large peak values were recorded for this variable. During knee extensions,
contractions of the quadriceps causes anterior tibial displacement (relative to the femur),
resulting in anterior shear forces at the knee (Shimokochi & Schultz, 2008). The hamstrings have
the potential to counteract anterior shear forces at the knee through antagonistic contractions
during knee extensions (Kingma, Aalbersberg, & van Dieen, 2004). Powerful knee extensor
muscles such as the vastus lateralis and vastus medialis exhibit high levels of muscle activity
during the early portion of the drive phase (Janshen, Mattes, & Tidow, 2009). Additionally,
Koutedakis, Frischknecht & Murthy (1997) observed low knee flexor to extensor ratios in a
rowers, thus indicating a relative hamstring weakness. As such, large anterior shear forces may
arise from deficits in antagonistic co-contractions during knee extension. Furthermore, these
deficits in hamstring strength could be associated with back pain in rowing, due to its effect on
pelvic mobility (Koutedakis, et al., 1997). As such, it is possible that loading at the knee may
influence kinematics and loading at the lumbar-pelvic region.
Specifically around the hip, there were no changes in sagittal plane kinetics with respect to stroke
rate, but there were significant increases in hip abduction and external rotation moments with
higher stroke rates. This study investigated a population of elite female rowers. Previous
research comparing male and female rowers found hip rotation angles to increase with respect to
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stroke rate for women only (Murphy, 2009). Furthermore, it is well established that during
locomotion, female anatomical traits such as large pelvis width and quadriceps angle, cause
females to exhibit different kinematics compared to men during locomotion. These include
greater peak hip adduction, hip internal rotation and knee abduction angles (Arendt & Dick,
1995; Ferber, Davis, & Williams, 2003). Therefore, at higher stroke rates females may tend to
increase loading about the coronal and transverse planes, thus restricting changes in sagittal
plane dynamics. However, a direct comparison of joint loading between female and male rowers
is necessary in order to substantiate this suggestion.
It was previously mentioned that loading at the distal joints may influence kinematics and
loading of the lumbar-pelvic region. In fact, large forces and moments were recorded at L5/S1
during ergometer rowing, with peak compressive forces of 14.8 N/kg and extension moments of
up to 13.1 Nm/kg measured at Free Rate. Additionally, abduction and external rotation moments
about L5/S1 were also found to be relatively large, with peak values of 1.87 Nm/kg and 1.21
Nm/kg, respectively. L5/S1 abduction moments tended to remain high throughout the drive
phase, whereas their external rotation moments tended to increase as MHF approached. The
presence of kinematic asymmetry has been shown to increase lateral flexion and twisting loads
of the lumbar spine during lifting movements (Kingma et al., 1998). Murphy (2009) has shown
that significant lateral flexion of L5/S1 is present during the drive phase of rowing, thus there is
evidence that instability at the lumbar-pelvic region during the drive phase leads to
compensatory loadings about the lumbar spine.
A 12 month prospective study of injury rates in elite rowers found that the lumber spine was the
most commonly injured site of the body, with high training volumes on the ergometer being
strongly associated with this risk (Wilson, Gissane, Gormley, & Simms, 2010). This lends
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support to the idea that injuries to the intervertebral discs may result from cumulative trauma
produced by repeated application of load (McGill, 1998), such as those experienced during long
training sessions with more than 1000 strokes. Additionally, the compressive tolerance of the
spine is reduced in the final stages of full spinal flexion (Adams & Dolan, 1995). Increases in
peak L5/S1 loading occurred alongside increased L5/S1 ROM and reduced anterior pelvic tilt at
the catch. This suggests that deteriorations in posture and technique at higher work rates may
contribute to increased loading of the lower back. In turn, increases in L5/S1 ROM may be due
to the significant reduction in ankle ROM with respect to stroke rate. With progressively less
plantar flexion at the finish position of the stroke, it is possible that L5/S1 demonstrated greater
flexion at the catch and greater extension at the finish in order to maintain the same stroke
length.
Increasing L5/S1 forces and moments at higher work rates is unlikely to be a measure of greater
performance, as corresponding increases in external force production at the foot-stretchers and
handle were not observed. Previous studies have shown that at higher stroke rates anterior pelvic
tilt will diminish (McGregor, et al., 2004), and in this study reduced anterior pelvic tilt was
compensated through increased lumbar-pelvic flexion at the catch. Therefore, it is likely that
poor posture and lumbar-pelvic motion throughout the rowing stroke are related to the large
forces and moments which occur there. This is an area which requires further investigation,
particularly in relation to injury prevention and rehabilitation. The only external forces seen to
change at higher intensities were peak seat forces. Figure 3 shows that peak seat forces occur
close to the finish of the stroke, and it is likely that these occurred as a result of greater L5/S1
ROM, specifically greater L5/S1 extension at the finish of the rowing stroke.
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Large L5/S1 extension moments were present during the rowing stroke and increased with
respect to work rate. The highest compressive forces in this study were just under 2000 N, which
were lower than values presented in previous studies of 2700 N (Morris, Smith, Payne,
Galloway, & Wark, 2000) and 5500 N (Munro & Yanai, 2000). The National Institute for
Occupational Safety and Health recommend a safe action limit of 3433 N of compressive force
at L5/S1. With rowers experiencing forces close to 2000 N at a frequency of >1000 cycles a day,
it is likely that when combined with sub-optimal technique, chronic damage may accumulate
over time. Furthermore, it is probable that the model used in this study underestimates inter-
segmental loads due to net joint moments, rather than individual muscle forces being quantified
during the activity. Furthermore, the generalisation of anthropometic data collected from a non-
athletic population may not be appropriate for a group of elite rowers, and may again lead to
under-estimation of values. Nevertheless, it was possible to draw important conclusions
regarding inter-segmental loading during ergometer rowing by observing the change in the joint
loads between progressive steps. It would be interesting to investigate potential neuromuscular
mechanisms of the biomechanical changes seen in this study. Elite rowers spend the majority of
their training at lower stroke rates. Therefore sudden increases in stroke rate may affect their
learned motor sequencing strategy. Neuromuscular fatigue at higher stroke rates may further
affect the rowers’ ability to maintain an optimal sequencing strategy. To investigate this further,
wavelet analysis of lower limb and trunk muscle activity may aid understanding of
neuromuscular contributions to the kinetic and kinematic changes observed in this study.
Conclusion
Low and high intensity rowing requires different joint loading strategies during both the drive
and recovery phases of a rowing stroke. In particular, large L5/S1 extension moments and
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compressive forces were present during the rowing stroke, and these increased with increasing
stroke rates. Therefore, even within a highly skilled elite population, it seems that high intensity
rowing is achieved through relative increases in work done by the lower back, and this seems to
be implicated with less pelvic forward rotation at the catch. Greater L5/S1 loading at higher
stroke rates is unlikely to be a measure of greater performance, as corresponding increases in
foot-stretcher forces were not observed. In fact, it may be an indicator of technique declining at
higher stroke rates, as larger peak L5/S1 moments occurred alongside increases in L5/S1 flexion
and increased loading of the seat.
From a coaching perspective these results provide useful information regarding the consequences
of high training intensities, and suggests that work that can be done in training towards
minimising technique deteriorations at higher stroke rates. Technique deteriorations that occur
when training at high intensities can lead to greater lumbar-pelvic loading, which has the
potential to result in chronic back pain over a long period of training. Therefore, increases in
work at the lumbar spine and the reductions in lower limb joint work should be considered by
coaches when developing training plans, with emphasis placed on maintaining a good technique
at higher rowing intensities.
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Bechard, D. J., Nolte, V., Kedgley, A. E., & Jenkyn, T. R. (2009). Total kinetic energy production of body segments is different between racing and training paces in elite Olympic rowers. Sports Biomechanics, 8(3), 199-211. doi: Pii 915131555
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Table 1: Kinetic, kinematic and performance parameters recorded from the ergometer step test.
Performance Kinematics Kinetics
Resultant foot force (N/kg) 3D ankle angles 3D ankle forces and moments
Vertical seat force (N/kg) Knee sagittal angle 3D knee forces and moments
Handle force (N/kg) 3D hip angles 3D hip forces and moments
3D L5/S1 angles 3D L5/S1 forces and moments
Table 2: Average stroke rate, distance rowed, 500 m split times and stroke length across the four stages of the step test.
Stroke rate (strokes per
minute)
Distance rowed (m)
500 m split time (s)
Stroke length (cm)
Rate 18 18.3 ± 0.5* 736.9 ± 17.2* 121.8 ± 2.9* 146.8 ± 6.8
Rate 24 24.0 ± 0.9* 800.1 ± 17.9* 112.5 ± 2.5* 144.4 ± 5.8
Rate28 28.0 ± 1.2* 837.4 ± 22.6* 107.5 ± 2.8* 142.5 ± 6.1
Free Rate 31.3 ± 1.9* 867.8 ± 21.5* 103.9 ± 1.7* 139.1 ± 6.3
*significantly different from all other stroke rates (p<0.001)
FIGURE LEGEND
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Figure 1: Two-dimensional representation of a five segment closed-chain link-segment model of
the foot, shank and thigh, pelvis and lumbar spine. Inset shows forces and moments acting on a
given segment. Md and Mp are distal and proximal moments, respectively. Fx and Fy are vertical
and horizontal intersegmental forces. Rx and Ry are vertical and horizontal intersegmental
reaction forces. Black arrows represent external forces acting on the foot stretcher and seat.
Figure 2: Peak force recorded at the foot-stretchers, seat and handle across four incremental
stroke rates.
Figure 3: Handle, seat and foot stretcher forces of a single representative subject shown over a
time normalised stroke cycle, for Rate 18 and Free Rate.
Figure 4: Group mean ± standard deviation of 3D moments at the ankle, knee, hip and L5/S1 for
Rate 18 (solid line) and Free Rate (dashed line). Positive values are extension, abduction and
internal rotation. Solid and dashed vertical lines represent the average finish position (% stroke
cycle) for rate 18 and free rate, respectively.
Figure 5: Group mean ± standard deviation of 3D forces at the ankle, knee, hip and L5/S1 for
Rate 18 (solid line) and Free Rate (dashed line). Positive values are lateral, tensile and anterior
shear forces. Solid and dashed vertical lines represent the average finish position (% stroke
cycle) for rate 18 and free rate, respectively.
Figure 6: L5/S1, hip, knee and ankle range of motion in the sagittal plane across four
incremental stroke rates. * significantly different from Rate 18 and Rate 24 (p<0.05).
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