Baseball Hitting Mechanics

8/4/2019 Baseball Hitting Mechanics

1/9

Hitting a Baseball: A Biomechanical DescriptionChristian M. Welch, BS 'Scott A. Banks, PhDFrank F. Cook, MD 3Pete Draovitch, MS, PT, ATC, CSCS4

or as long as the game ofbaseball has been played,hitting has intrigued play-ers, coaches, and research-ers alike. Advancing tech-

nology has facilitated the ability tocapture the act of hitting and analyzethe mechanics involved. In 1961,Race (14) , with the aid of a 16m mmovie camera and the swings of 17minor league players, presented oneof the first effective qualitative andquantitative breakdowns of the over-all swing. The concepts of kineticlinking, angular measurement, bal-ance, and judgment time were intro-duced and supported with data.

In subsequent studies, the abilityto transform standard film and videointo a three-dimensional representa-tion of the captured hitting motionnot only increased the accuracy ofmeasurement, but introduced newanalysis parameters. Using this tech-nology, Shapiro (17) , in a study ofbat dynamics, described the bat'smovement during the swing usingthe three-dimensional componentsof its motion, while DeRenne (4),through a series of studies, developedan elaborate method of assessing ahitter's mechanical efficiency.

The combination of biomechani-cal research and traditional baseballknowledge has begun the process ofresearch and investigation (1,6,7,12,18.19). The missing component tothis point has been the ability tobuild a comprehensive understandingof the body's natural coordinationand movement during the swing.Once a baseline understanding has

A tremendous amount of time and energy has been dedicated to the development ofcond itioning programs, mechanics drills, and rehabilitation protocols for the throwing athlete. Incomparison, a significantly smaller amount has been spent on the needs of the hitting athlete. Beforethese needs can be addressed, an understanding of mechanics and the demands placed on the bodyduring the swing must be developed. This study uses three-dimensional kinematic and kinetic data todefine and quantify biomechanics during the baseball swing. The results show that a hitter starts theswing wi th a weight shih toward the rear foot and the generation of trunk co il. As the hitter stridesforward, force applied by the front foot equal to 123% of body weight promotes segment acceleration around the axis of the t ~ n k .he hip segment rotates to a maximum speed of 714Ysecfollowed by a maximum shoulder segment velocity of 9 3 7 % ~ .The product o f this kinetic link is amaximum linear bat velocity of 31 ds ec . By quan tikng the hitting motion, a more educatedapproach can be made in developing rehabilitation, strength, and condi tioning programs for thehitting athlete.Key Words:biomechanics, baseball, batting' President, Human Performance Technologies, Inc., 825 South U.S. Highway One, Suite 200, jupiter, FL33477Technical Director, Orthopaedic Research Laboratory, Good Samaritan Medical Center, West Palm Beach, FL' o-Medical Director, Orthopaedic Research Laboratory, Good Samaritan Medical Center, West PalmBeach, FLConsultant, Orthopa& Research Laboratory, Good Samaritan Medical Center, West Palm Beach, FL

been developed, we can move on toinvestigate the intricacies of specificmechanical parameters and relatethis information to a hitter's ability atthe plate. The goal of this study wasto develop an understanding of base-line mechanics through quantitativebiomechanical data and provide apreliminary synthesis of results forthe application to training and reha-bilitation.

METHODSTesting Procedure

Thirty-nine (25 right-handed hit-ters and 14 left-handed hitters) maleprofessional baseball players were

tested at an indoor biomechanics fa-cility. In order to maintain uniformityin the population used for this study,only the right-handed subjects wereconsidered. Of the 25 right-handedhitters, only those who had at least100 "at-bats" and a minimum battingaverage of .250 during the 1993 sea-son were included. Each minorleague player's batting statistics werecombined for all clubs and organiza-tions played with during the 1993season.

Data included in this study, basedon the defined criteria, were gener-ated from seven subjects. The meanbatting average for the subjects was.293 ( t OX) and the average num-ber of "at-bats"was 273 (t 168). The

JOSPT Volume 22 Number 5 November 1995

Journal of Orthopaedic & Sports Physical TherapOfficial Publication of the Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Associa


2/9

R E S E A R C H S T U D Y

seven subjects' level of play rangedfrom minor league to major league.At the time of testing, six subjectswere playing in the minor leaguesand one subject was playing in themajor leagues. The average weightwas 844 N (2 24 N) and the averageheight was 1.83 m (2. 06 m).

Preceding data collection, a sys-tem of 23 reflective markers wasplaced on the hitter, bat, and ball.Markers applied directly to the skinwere held securely in place with softfoam adhesive biofeedback pads(Davicon, Billerica, MA). "Stick"markers, pelvis markers, and wristmarkers were held in place usingNeoprene wraps an d VelcroTM.Marker placement (Figure 1) includ-ed: I ) right and left shoulder placedat the acromioclavicular joint,2) neck placed a t C7 of the spine,3) right and left elbow placed at thelateral epicondyle, 4) right and leftwrist placed dorsally between the ul-nar and radial styloid process, 5) sa-crum marker placed at L5 of thespine, 6) right and left anterior supe-rior illiac spine, 7) right and leftthigh using a "stick" marker to definethe frontal plane, 8) right and leftknee placed at the joint line, 9) right

Once a baselineunderstanding has

been developed, wecan move on toinvestigate the

intricacies of specificmechanical parameters.

and left shank using a "stick" markerto define the frontal plane, 10) rightand left ankle placed at the lateralmalleoli, 11) right and left forefootplaced on top of the shoe, 12 ) reflec-tive tape on the ball, and 13) reflec-tive tape around the bat handle just

FIGURE 1. Marker placement for subject, bat, and ball.

above the hands and at the top ofthe barrel end of the bat.

After the subject had warmed upand the reflective markers had beensecurely applied, he was instructed tohit a number of baseballs off of astandard batting tee. The tee wasplaced in the hitting area so that thedesignated batter's box was com-prised of two force plates. The forceplates were arranged side by side sothat the subject could comfortablyplace each foot on an individualforce plate. The tee was adjusted tothe subject's preferred position andheight to hit a line drive "up themiddle," based on both verbal com-munication with the subject andwarm-up performance. The subjectwas then asked to hit a ball markedwith reflective tape for data collec-tion. The three best line drive hitswere used for data in this study. Cri-teria for determining the three bestline drive hits included verbal com-munication with the subject, contact,flight of the ball, and accuracy ofdata collection.

During data collection, the move-ment of the reflective markers was

simultaneously captured by six cam-eras at a rate of 200 frames per sec-ond (Motion Analysis Corporation,Santa Rosa, CA). The informationcollected by each of the six cameraswas then mathematically processedand the three-dimensional movemenof each marker was calculated usingExpert Vision digitizing software (Motion Analysis Corporation, SantaRosa, CA). In addition, the three-dimensional ground reaction forceswere measured for each foot at a ratof 1000 samples per second using twsixchannel force plates (AdvancedMechanical Technology, Inc., New-ton, MA). Both the motion and theground reaction force collection sys-tems were electronically synchronizedto begin collection simultaneously.

The parameters chosen to por-tray the motion of the baseball swingwere consequently based on the bio-mechanical data. Kinematics and ki-netics were calculated using thethreedimensional information generated during a test. The relative movement of the reflective markers withinthe global reference frame andbody/joint reference frames definedVolume 22 Number 5 November 1995 JOSP


3/9


8: STRIDE DlRECTlON8:FRONT FOOT POSITIONf :STRIDELENGTH (B)

A: SHOULDERSB: HIPSC: ARMS (C)

FIGURE2. Batter orientation and movement. A) Global reference frame. B) Stride parameters. C)Segmental rotation around axis of the trunk (AOT).general kinematics, including dis-placement and velocity for both lin-ear and angular measurements. Theapplication of force by each foot tothe ground relative to the coordi-nates of the global reference framedefined kinetics.PARAMETER DESCRIPTION/CALCULATIONGlobal Reference Frame

The global reference frame wasdefined as the three-dimensional co-ordinate system in which the relativemovement of the body was measured(Figure 2A). Each of the three axeswere perpendicular to each otherand defined three planes of move-ment. For this study, the positive Xaxis was the most crucial because itwas used as a reference for the seg-ment rotation and stride parameters.It was defined as the direction fromhome plate to the pitching rubberand parallel to the surface of the bat-ter's box. When looking in the posi-tive X direction, positive Z was de-fined as pointing superiorly and

positive Y was defined as pointing tothe left.Ground Reaction Forces

Ground reaction forces repre-sented the interaction of the bodywith the ground (10). The three-dimensional force applied to theground by both feet was measuredduring each swing. Each individualcomponent of applied force (X, Y, Z)in the global reference frame (Figure2A) was expressed as a value in N forthe left and right foot. The resultantmagnitude of force for each foot wasexpressed as a value in N as well as apercentage of body weight.Center of Pressure/Center of Mass

The relative movement of thecenter of pressure between the twofeet and the body's calculated centerof mass in the global X direction wasmeasured as an indication of dy-namic balance and forward momen-tum (3,4,15). The position of thecenter of pressure between the twofeet was calculated by first weighting

The three-dimensionalposition of the center

of mass for eachindividual segment wassummed to produce

the position of thewhole body

center of massin global coordinates.

the position of the center of pressureby the magnitude of the downwardforce for each individual force plate(each foot). The two weighted posi-tions were then averaged to producethe center of pressure between thetwo feet in global coordinates. Thecenter of mass was calculated usingsegment center of mass and segmentbody weight percentage measure-ments presented by Contini (3).The



4/9

R E S E A R C H S T U D Y- --- - - - - ..---.--..--..--- ?. - - - . -. .- - -three-dimensional position of thecenter of mass for each individualsegment was calculated, weighted byits percentage of body mass, andsummed to produce the position ofthe whole body center of mass inglobal coordinates.Stride

As the hitter strode forward andthe front foot made contact with theground, the length and direction ofthe stride as well as the position ofthe left (front) foot were defined(Figure 2B). Stride length was thedistance between the right and lefttoe at foot down. It was expressed asa value in cm and as a percentage ofthe width of the hips from right hipcenter to left hip center. The direc-tion of the stride was the angleformed between the vector fromright to left toe and the global X axis(+ = closed, - = open ). The posi-tion of the left foot was the angleformed between the vector from leftankle to left forefoot and the globalX axis (+ = closed, - = open).Both were expressed in degrees.

Flexion and extension of the leftand right knee as well as the left andright elbow (8) were defined as theabsolute angle formed between theproximal and distal segments com-prising the joint. Full anatomical ex-tension of the joint corresponded to0" while full anatomical flexion ofthe joint corresponded to 180".

Segment RotationA hitter's ability to utilize a ki-

netic link to generate bat speed de-pended heavily on the interaction ofthree body segments (4.1 1,13). Thesegments were the hips, shoulders,and the arms (Figure 2C). The hipswere defined as a vector from theright hip to the left hip. The shoul-ders were defined as a vector fromthe right shoulder to the left shoul-

de r and the arms were defined as avector from mid-shoulders to mid-wrists. Their interaction was the rota-tion around a common axis. This axiswas defined as the axis of the trunkfrom mid-hips to mid-shoulders andthe rotation was measured with re-spect to the global X axis.

The orientation of the trunk axiswas also measured. It was defined asthe angle formed between the vectorrepresenting the trunk and the globalZ axis in the median plane (+ =flexion, - = extension) and thefrontal plane (+ = right, - = left)of the body.Bat Movement

The movement of the bat can bedescribed by bat lag (2,4,11) and thelinear velocity of the end of the bat(9,17). For this paper, bat lag wasdefined as the absolute angle formedbetween the vector representing thebat from the handle to the barreland the vector from mid-shoulders tomid-wrists. When the bat was fullyextended away from the arms andboth the vector representing the batand the vector representing the armswere in line, the corresponding batlag angle was 180". The linear veloc-ity at the barrel end of the bat wasdefined by the first derivative of eachof the component displacements inthe global reference frame (Figure2A) and the resultant magnitude.Batting Events

For the purpose of describing ahitter's natural coordination andmovement, three key events werechosen as both landmarks for refer-ence and for the identification of keymechanical transitions. The first wasfoot off. It was defined as the instantthe left (front) foot broke contactwith the ground and began thestride. Th e second was foot down. Itwas defined as the instant the leftfoot made full contact with theground, ending the stride and begin-ning closed chain energy transfer.

The third was ball contact. It was de-fined as the instant the bat madecontact with the ball, beginning thefollow-through.

RESULTSBefore the parameters were cal-

culated, all threedimensional datawere smoothed using a fourth-order,zero phase shift, low pass Butterworthfilter with a cut-off frequency of 13.3Hz. The individual data included foreach of the seven subjects were gen-erated as the average of their threeline drive swings. Mean kinematicand kinetic data 5 standard deviatiofor the seven subjects are presentedin Tables 1-4.BIOMECHANICAL DESCRIPTION

The swing was initiated with aweight shift toward the right (back)leg. At approximately the same time,the upper body rotated in a clockwisdirection (Figure 2C) around theaxis of the trunk, initiated by thearms and shoulders, and followedclosely by the hips. This began thecoiling process.

Foot OffIStrideImmediately following the initia-

tion of coiling, the left (front) legwas lifted and the left foot broke contact with the ground (foot off), in-creasing the total force applied bythe right (back) foot to a value of102% of body weight. Part of the to-tal force applied by each foot wasshear force acting parallel to theground in the global X and Y direc-tions. Ground reaction to the shearforce promoted the linear and rota-tional movement of the hitter. Atfoot off, the right foot applied 146 Nof shear force in the negative X di-rection and 26 N in the positive Ydirection. The right knee was flexedat 32" and the center of pressure hadmoved in the negative X directiontoward the right foot to a point 20cm behind the center of mass. TheVolume 22 Number 5 November 1995 JOSP


5/9

Parameter Foot Off Foot Down Ball Contad- - -X SD X SD X SDRight FootTotal force (N )Percent of body weight

X component (N )Y component (N )Z component (N )

Left FootTotal force (N) 1007 472 709 270Percent of body weight 123 63 84 32X component (N ) 292 167 153 146Y component ( N ) -280 125 28 65Z component (N ) -91 7 429 -672 270-

SD = Standard dwi~tion.TABLE 1. Force applied by each foot at key points in swing.

-Parameter X SDHMRV ("lsec) 714 76SMRV ("Isec) 937 102AMRV (O/sec) 1160 96BLMRV ("Isec) 1588 162BMLV (rnfsec) 3 1 2

the same time, continued in a clock-wise rotation around the axis of thetrunk, increasing the coil of the u pper body against the movement ofthe hips and shoulders.

SD = Standard &viation.HMRV = Hip segment maximum rotational velocity.SMRV = Shoulder segment maximum rotationalvelocity.AMRV = Arm segment maximum rotational velocity.BLMRV = Bat lag maximum rotational velocity.BMl V = Bat maximum linear velocity.TABLE 2. Maximum segment rotational velocitiesand bar linear velocity.

arms, which led the clockwise rota-tion, had rotated to 150" at foot off,while the shoulders had rotated to30". followed by the hips at 18". Thisrotation occurred around an axis ofthe trunk that was fairly upright. Thetrunk was flexed forward 21" and lat-erally left 6".As the stride continued towardfoot down, the hips rotated to a max-imum position of 28", 0.350 secondsprior to ball contact. At that instant,the hips began to rotate in a counter-clockwise direction. The shoulders,however, continued in a clockwisedirection, increasing the coil of thetrunk until they reached a maximumrotation of 52", 0.265 seconds priorto ball contact. At that instant, theychanged direction and followed thelead of the hips in a counterclockwiserotation toward the ball. The arms, at

Foot ContactA. the left forefoot made contact

with the ground, the length and di-rection of the stride were defined.The mean stride length was a dis-tance of 85 cm or 380% of hip width.The direction of the stride was 12"(closed) and the position of the footas it began to make contact with theground was 67" (closed) (Figure 2B).I t was with left foot contact that thehitting action became a closed chainenergy transfer. The arms which hadincreased the coil of the upper bodyby continuing in a clockwise rotationaround the axis of the trunk reacheda maximum position of 185" and be-gan a counterclockwise rotation.

Weight was shifted forward as theheel of the left foot made contactwith the ground (foot down). Theleft foot was in a position of 61"(closed) and was applying a totalforce equal to 123% of body weightto the ground. As a part of the totalforce applied by the left foot, 292 Nof shear force were applied in thepositive X direction and 280 N ofshear force were applied in the nega-tive Y direction. The total force a p

plied by the right foot had decreasedto 58% of body weight. As a part ofthe total force applied by the rightfoot, 80 N of shear force were a pplied in the negative X direction and184 N of shear force were applied inthe positive Y direction. At that pointthe center of pressure had made adrastic shift forward in the X direc-tion to a point 20 cm ahead of thecenter of mass.

With the weight shift forward andthe shear force applied in the X andY direction by both the left and rightfoot, segments were now acceleratedto maximum velocities a. he bodycoordinated an effort to produce batspeed. The left leg extended at theknee, pushing the left hip backward,while the right leg pushed the righthip forward, creating a counterclock-wise acceleration of the hips aroundthe axis of the trunk. The rotationalvelocity of the hips increased until itreached a maximum of 714"/sec,0.075 seconds prior to ball contact.The shoulders and arms, followingthe lead of the hips, accelerated to amaximum rotational velocity of 937"/sec and 1160/sec, respectively, 0.065seconds prior to ball contact.

As a result of the body's coordi-nation, the bat also moved aroundthe axis of the trunk, increasing inboth angular velocity and linear ve-locity. The two main components oflinear movement were anterior or



6/9

FootOff Foot Down Ball Contact- - -X SD X SD X SD

Hip rotation ("1Shoulder rotation (")Arm rotation ("1Bat lag (1Right knee flexiodextension "1Left knee flexionlextension "1Right elbow flexionlextension "1Left elbow flexiodextension (")Trunk flexiodextension ("1Trunk lateral flexion ("1Cop-Com (crn)SD = Standard devia tion.Cop-Com = The relative difference n position o f he center of pressure between the two feet and the calculated whole body center of mass in the globa lX direction I(-) centeof pressure behind center of mass, (+ I center o f pressure ahead of center of mass/.TABLE 3. Position of body parameters at key points in swing.

Parameter x SDStride length (crn) 85 12Stride as percent of hip wid th 380 75Stride direction (") 12 3Lead foot position ("1 61 11-

SO = Standard devia tion.TABLE 4. Stride parameters.

away from the body in the negativeYdirection and downward in the nega-tive Z direction. The anterior move-ment of the bat away from the bodyincreased to a velocity of 19 m/sec at0.040 seconds before ball contact. Atthe same time, the downward move-ment of the bat increased to a maxi-mum velocity of 16 m/sec. Th e linearmotion of the bat then became domi-nated by an increase in the positive Xdirection toward the ball, while the Yand Z components of linear velocitydecreased in magnitude (Figure 4).

Nearing the point of impact, thehitter utilized the last bit of angularspeed and kinetic link as the speedof bat lag or uncocking reached itsmaximum value of 1588"/sec at 0.020seconds before ball contact (Table 2,Figure 3). Th e bat was then driven toits maximum linear velocity of 31m/sec in unison with the right armmaximum extension velocity of 9487sec, both occurring 0.015 secondsbefore ball contact.

Ball ContactAt ball contact, the body had

used both coordination and positionto generate bat speed and direction.The linear speed of the bat had de-celerated slightly to 29 m/sec, butthe most significant component ofthat speed was directed in the posi-tive X direction toward the ball. Theleft leg was acting as a block, flexed15" at the knee and applying a totalforce to the ground equal to 84% ofbody weight. The right leg was nowacting in a support capacity, flexed45" at the knee and applying a totalforce of 16% of body weight to theground. The trunk had movedthrough a significant range of motionin an effort to assist in bat positionand become an extension of thefront leg's block. It had movedthrough a range of 30" backward to aposition of 9" of trunk extension. Ithad also moved through a range of26" right to a position of 20" of rightlateral flexion.After ball contact, the body actedto slow itself and the bat through ec-centric contraction and the diffusionof energy through the larger musclegroups (5). This study focused on theswing from foot off to ball contact;however, insight into the follow-through portion and the decelerationof segments can be gained using de-

scriptions by Shaffer et al (16). Gar-hammer (5), and DeRenne (4).

DISCUSSIONTo begin the process of building

an understanding of mechanics andthe demands placed on the body during the swing, it is essential to have abase understanding. The intent ofthis paper is to provide the first stepthrough a quantitative biomechanicaldescription of hitting a baseball. Thedescription presented is not only fun-damental to the knowledge of themechanics of hitting, but also for theapproach to analyzing a hitter's per-formance at the plate. A subject-posi-tioned batting tee was used in thisstudy to try to eliminate the variablesof recognition, reaction, and adjust-ment to a pitched baseball. The re-sulting data, summarized in Tables1-4, provide a very useful guide forunderstanding the general principlesof both the mechanics and the physi-ology involved in hitting a baseball.The results also provide a foundationfor not only studying the individualparameters more thoroughly, butstudying variations within and be-tween individual hitters.

Much like a golfer, the hittergenerates bat speed using a kineticlink (11.13). A kinetic link can bebriefly summarized as large base seg-ments "passing" momentum toVolume 22 Number 5 November 1995 JOSFT


7/9


FIGURE 3. Sequence of events occurring in a baseball swing in relation to ball contact Events: I) foot off,2) maximum hip rotation, 3) maximum shoulder rotation, 4 ) maximum arm rotation, 5) foot down, 6)maximum hiprotational velocity, 7)maximum shoulder and arm rotational velocity, 8) maximum Y and Z components of batlinear velocity, 91 bat lag maximum rotational velocity, 10)maximum bat linear velocity and maximum right elbowextension velocity, 1 1 ) maximumX component ofbat linear velocity, 12)ball contact, and 131maximum lefi elbowextension velocity.

smaller adjacent segments. The basicprinciple is that a system of segmentsmoving at a certain velocity has mo-mentum. When a large base segmentdecelerates, the velocity of the re-maining system increases as it as-sumes the momentum lost by thebase segment. In the particular in-stance of hitting mechanics, the seg-ments are interrelated via the muscu-loskeletal system. This system canpotentially accelerate and deceleratethe segments through the applicationof muscular force, therefore, addinga second component to the kineticlink. Optimizing both the mechanicaland physiological components createsthe "motivation" for a majority of themechanics incorporated during thehitting motion. Consequently, a largepart of a hitter's mechanical perfor-mance is derived from maximizingthe kinetic link parameters.

A hitter starts the swing with theclockwise rotation (right-handed hit-ter) of the arm, shoulder, and hipsegments, while shifting weight to-ward the rear foot. This action canbe considered the act of loading orcoiling. The hitter moves segmentsopposite of both the intended rota-tional (counterclockwise for right-handed hitter) and linear (forward inthe global positive X) direction be-fore accelerating into ball contact.This action defines two componentsof motion: rotational and linear.

The rotational component in-volves the movement of segmentsaround the axis of the trunk. The

important factors to consider duringthe stride are the amount of clock-wise rotation by each segment andthe sequence of the initial movementof each segment in the counterclock-wise (intended) direction. As shownin the results (Figure 3), it is impor-tant that the hip segment starts coun-terclockwise rotation before theshoulder segment, which, in turn,should start before the arm segment.This sequence allows the kinetic linksystem to begin to incorporate themusculature of the trunk and upperextremity through preload. Excessiveclockwise rotation of individual seg-ments or all of the segments maycontribute to a reduction of muscularefficiency as well as produce a disruption in the sequencing of segments.In turn, the disruption of the se-quence of each segment's initial rota-tion in the counterclockwise (intend-ed) direction interrupts the hitter'sability to fully incorporate the trunkand upper extremity musculature.

The linear component is the for-ward movement (global positive Xdirection) of the body. By shiftingweight to the rear foot, the hitter hasmoved the center of pressure behindthe position of the center of mass(global X direction). Data in Table 3show that the center of mass can be20 cm ahead of the center of pressure. This moves the body out of anequilibrium state where the center ofpressure and center of mass arealigned (15). causing the body to"motivate" toward the direction of

the center of mass. This, combinedwith the application of shear force bythe right foot (rear) in the globalnegative X direction, drives the hitterin a linear fashion toward the ball.

As the hitter's stride foot makescontact with the ground, the linearcomponent and the rotational com-ponent begin to interact with eachother. The interaction of the twomovements determine how the ki-netic link will be utilized. At footdown, the center of pressure has nowmoved ahead of the center of mass(Table 3) . The application of shearforces by the left and right foot (Ta-ble 1) produce a force couple at thehip segment, facilitating its counter-clockwise acceleration around theaxis of the trunk. At this point in theswing, the hitter can mechanicallyemphasize either the rotational orlinear component. If the rotationalcomponent is emphasized, the centerof pressure aligns itself with the cen-

Proper timing facilitatessuccessively higherrotational velocities.

ter of mass between both feet. Thisallows significant shear force to beapplied by each foot and increasesthe force couple applied to the hipsegment. If the linear component isemphasized, then the center of pres-sure stays in a forward position at thelead foot and the center of massmoves to align itself over the leadleg. In this case, the only significantshear application is produced by thelead foot, reducing the force coupleapplied to the hip segment for accel-eration. The results of this studydemonstrate that the emphasis ofrotational and linear movements var-ies between hitters as shown by highstandard deviations in shear forceapplication (Table 1) and center ofmass/center of pressure relativemovement (Table 3).

JOSFT Volume 22 Number 5 November 1995


8/9

leftX COMPONENT

(m/s>

right

posteriorY COMPONENT

(m/4

anterior

Z COMPONENT(m/4

down

LINEAR VELOCITY(m/s>

-1.0 -0.8 -0.6 -0.4 -0.2 0.0Time (s)

FIGURE 4. Component and resultant linear velocities of the bat during a ~ ypical aseball swing. Vertical axis isvelocity (d se cj and horizontal axis is time (seconds). Time of 0.0 represents ball contact.

Regardless of individual mechan-ics, the hip segment is acceleratedaround the axis of the trunk to amaximum velocity. This increases thevelocity of the entire system movingin the intended direction. The hipsegment is then decelerated, as theshoulder segment is accelerated, uti-lizing the kinetic link principle (4,11,13).Again, timing is essential for the

most efficient acceleration of eachsuccessive segment, culminating withthe bat. Proper timing facilitates suc-cessively higher rotational velocities(Table 2) . which, in turn, producebat speed and power. Conversely, if asmaller adjacent segment reaches amaximum velocity before the preced-ing base segment, then it has lost theability to make full use of the speed

and, consequently, the momentumgenerated by the base segment.

Although these data are a preliminary step needed to lay the groundwork for more indepth study, theycertainly serve as pertinent informa-tion for the clinician, whether that bethe physician, therapist, trainer, orcoach. The information in this paperprovides a fundamental understand-ing of hitting biomechanics, whichcan serve as the basis for a structuredand informed approach to the reha-bilitation and training of the hittingathlete.

SUMMARYThe purpose of this study was toprovide a foundation for the biome-

chanical study of hitting and the pre-liminary synthesis of data for applica-tion to the rehabilitation and trainingof the hitting athlete. This goal isachieved by presenting a biomechani-cal description of hitting a baseballusing the mean kinematic and kineticdata of seven professional baseball players in a controlled environment Theemphasis of the data presented is theportrayal of the body's natural motionand coordination.Additional studies are being con-ducted and will focus specifically on:1) the relationship between the rota-tional and linear components ofweight transfer, 2) the specific inter-action of segments involved in thekinetic link, and 3) the accelerationand power with which the bat movesinto contact with the ball. Each ofthe additional studies will concen-trate on a specific area of biomechanics introduced in this study. This willallow the concepts and principlesinvolved to be fully investigated. Thecombination of all these studies willprovide a comprehensive understand-ing of the biomechanics and coordi-nation involved during the baseballswing. In addition, they will provide astepping stone for the total under-standing of a hitter's performance atthe plate. JOSPTVolume 22 a Number 5 November 1995 JOSP


9/9

. . . , . . . . . .. .. . R E S E A R C H S T U D Y-. .. *.-- - -. .. .--. --.---..,- ..--..- .. -.-". . - . - . . ...

ACKNOWLEDGMENTSThe authors acknowledge thecontributions of Sean Cunningham,ATC, CSCS of the Montreal Expos aswell as the entire Montreal Exposorganization for their baseball guid-

ance and expertise. We also thankthe athletes who participated in ourstudy and continue to support ourongoing effort to study injury andperformance mechanics.

REFERENCES1. Breen JL: What makes a good hitter?JHealth Phys Ed Rec 38:36-39, 19672. Budney DR, Bellow DG: Kinetic anal-ysis of a golf swing. Res Q 50(2):171-179, 19793. Contini R: Body segment parameters.Part 11. Artif Limbs 16(1):1-19, 19724. DeRenne C: High-Tech Hitting: Sci-ence vs. Tradition, St. Paul, MN: WestPublishing Company, 1993

5. Garhammer J: A kinesiological analysisof hitting for baseball. Natl Strength Con-ditioning Asxx J 5(2):6 7, 70-7 1, 19836. Lau C, Glombrenner A, LaRussa T: TheArt of Hitting .300, New York, NY: Vi-king Penguin, 19917. Lefebvre ): Hitting the baseball: Let'sunderstand the process. Natl StrengthConditioning Assoc J 5(2):6 7, 70-71,19838. Mclntyre DR, ffautsch EW: A kine-matic analysis of the baseball battingswings involved in opposite-field andsame-field hitting. Res Q Exerc Sport53(3):206-2 13, 19829. Messier Sf, Owen MG: Bat dynamicsof female fast pitch softball batters. ResQ Exerc Sport 55(2):141-145, 1984

10. Messier Sf, Owen MG: The mechanicsof batting: Analysis of ground reactionforces and seleaed lower extremity kine-matics. Res Q Exerc Sport 56(2):138-143, 198511. Milburn PD: Summation of segmentalvelocities in the golf swing. Med SciSports Exerc 74:60-64, 198212. Miller RG, Shay CT: Relationship of re-

action time to the speed of a sohballRes Q 35(Suppl3):433-437, 196413. Putnam CA: Sequential motions obody segments in striking and throwingskills: Description and explanations.Biomech 26(Suppl):125-1 35, 198314. Race DE: A cinematographics and mechanical analysis of the external movements involved in hitting a baseball effectively. Res Q 32(3):394-404, 196115. Riley PO, Schenkman ML, Mann RW,Hodge WA: Mechanics of a constrained chair-rise. Biomech 24(1):77-85, 199116. Shaffer B, lobe FW, Pink M, Perry JBaseball batting: An electromyographicstudy. Clin Orthop 292:285-298, 19917. Shapiro R: Three-dimensional kineticanalysis of the baseball swing. Unpublished doctoral dissertation, Universityof Illinois at Urbana-Champaign, Urbana-Champaign, IL, 197918. Watts L: Classroom approach to batting. Scholastic Coach 35: 19-20, 196619. Williams T, Underwood): The Scienceof Hitting, New York, NY: Simon andSchuster Inc., 1986


Documents

Baseball Hitting Mechanics