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Kinematic analysis of shot-putting performedby wheelchair athletes of different medicalclassesJohn W. Chow , Woen-Sik Chae & Michael J. CrawfordPublished online: 09 Dec 2010.

To cite this article: John W. Chow , Woen-Sik Chae & Michael J. Crawford (2000) Kinematic analysis of shot-putting performed by wheelchair athletes of different medical classes, Journal of Sports Sciences, 18:5,321-330, DOI: 10.1080/026404100402386

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Kinematic analysis of shot-putting performed bywheelchair athletes of diþ erent medical classes

JOHN W. CHOW,* WOEN-SIK CHAE and MICHAEL J. CRAWFORD

Department of Kinesiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA

Accepted 2 January 2000

The aim of this study was to identify those kinematic characteristics that are most closely related to an athlete’smedical classi® cation and measured distance of a put. Two S-VHS camcorders (60 ® elds per second) were usedto record the performance of 17 males of diþ erent classes. Each participant performed six trials and the best trialfor each was selected for analysis. Three-dimensional kinematics of the shot and upper body segments at theinstant of release and during the forward thrust (delivery) were determined. The average speeds and angles of theshot at release for diþ erent classes (5.3± 7.8 m ´s - 1 and 21.2 to 34.4°, respectively) were smaller than thoseexhibited by elite male able-bodied throwers. The height of the shot at release, the angular speed of the upperarm at release, the range of motion of the shoulder girdle during the delivery, and the average angular speeds ofthe trunk, shoulder girdle and upper arm during the delivery, were all signi® cantly correlated with both theclassi® cation and measured distance (P < 0.05). The results indicate the importance of achieving a high averageangular speed for each upper body segment during the delivery.

Keywords: athletics, biomechanics, disability, ® eld events.

Introduction

Opportunities for sports competition among athleteswith locomotive disabilities have increased in the lastfew decades (DePauw and Gavron, 1995). Athleticsare oý cial events of the Paralympic Games and arepopular among wheelchair athletes. Previous studieson wheelchair athletics have focused on the propulsionof racing wheelchairs (e.g. Van der Woude et al., 1988;M× sse et al., 1992; Wang et al., 1995; Goosey et al.,1997; Cooper, 1990). Few attempts have been madeto establish the kinematic characteristics of the ® eldevents, such as shot put, discus and javelin throws(Chow and Mindock, 1999). It is apparent that baselinedescriptive data are required for teaching and instruc-tion purposes and to build the foundation for futureresearch activities in these areas.

Competitors in wheelchair athletics are classi® edbased on the level of spinal cord injury and the controland strength of diþ erent muscle groups (Atlanta Para-lympic Organizational Committee, 1996; see Appendix).

* Address all correspondence to John W. Chow, 241D Freer Hall,Department of Kinesiology, 906 South Goodwin Avenue, Universityof Illinois at Urbana-Champaign, Urbana, IL 61801, USA. e-mail:j-chowl@uiuc.edu

For the ® eld events, there are eight diþ erent classes,F1± F8 (neurological levels C6± S2). However, the shotput is not held for F1 athletes. All athletes put a 4.0 kgshot except those in classes F2 (2.0 kg), F3 (3.0 kg) andF8 (5.0 kg). Shot-putters perform puts from custom-made chairs that are anchored to the throwing circleby cables. Most athletes design their chairs and adoptsitting positions that suit their muscle function andstrength, ¯ exibility and personal preference (Fig. 1).Almost every competitor uses some kind of strap to tiehis hips and one or both legs to the chair to stabilize thelower body. Because of the diþ erences in disability,chair designs and sitting positions, athletes may usea variety of putting techniques. The aim of this studywas to identify those kinematic characteristics that aremost closely related to the medical classi® cation andmeasured distance of a put.

Methods

Theoretical considerations

During the action of a put, at least one part of the upperleg or buttock must remain in contact with the seatcushion (for classes F2± F6), or at least one foot must

Journal of Sports Sciences, 2000, 18, 321± 330

Journal of Sports Sciences ISSN 0264-0414 print/ISSN 1466-447X online Ó 2000 Taylor & Francis Ltdhttp://www.tandf.co.uk/journals

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Fig. 1. The chair used by an athlete must be located inside the circle but the footrest(s) or part of the legs can protrude outsidethe circle (a). Some athletes of the lower classes hold on to the chair or a pole that is ® xed to the chair for additional support duringthe puts (b). The segmental model used in this study is de® ned by the mid-hips (A), mid-shoulders (B), right shoulder (C), rightelbow (D), right wrist (E) and third knuckle of the right hand (F).

remain in contact with the ground inside the circle (forclasses F7 and F8), until the shot is released (NationalWheelchair Athletics Association, 1992). As a result, themotion at the hips is minimal even for those participantswho have partial functions in the lower extremities. Forthe purpose of analysis, ® ve linked segments can beidenti® ed between the hips and the shot (Fig. 1b): thetrunk (from mid-hips to mid-shoulders), the shouldergirdle (from mid-shoulders to throwing shoulder), theupper arm (from shoulder to elbow), the forearm (fromelbow to wrist) and the hand (from wrist to thirdknuckle of hand). During a put, the kinematics of theshot are determined by the angular kinematics of these® ve segments (Fig. 2). Although some putters rockedtheir upper bodies back and forth several times prior tothe forward thrust before release (delivery), the presentstudy focused on the kinematic characteristics of theforward thrust and the release of the shot.

Figure 2 presents a shot put model showing thefactors that determine the measured distance of a put.In the second level of the model, a putter will lose dis-tance if the shot is released inside the circle and viceversa. In the third level, the ¯ ight distance is determinedby factors governing the trajectory of a projectile. Theheight of release is determined in part by the heightof the chair and the body position at the instant ofshot release. For the rest of the model, consider theangular motion of a body segment, the velocity ofthe distal end-point of the segment (nd) is determined bythe velocity of the proximal end-point of the segment

(np), the angular velocity of the segment (v), and therelative-position vector drawn from the proximal todistal end-points (rd/p):

nd =np + v ´ rd/p (1)

The magnitude of the second term on the right-handside of this equation is the product of the angularspeed of the segment and the length of the segment.During the forward thrust before the shot is released,the average angular acceleration of a segment (aÅÅ) is givenby:

aÅÅ= (vR - vB)/t (2)

where vB and vR are the angular velocities of thesegment at the beginning of the forward thrust and atrelease, respectively, and t is the time taken to completethe forward thrust. The average angular speed of asegment during the forward thrust (sÅÅ) is determinedusing the angular distance the segment travelled duringthe forward thrust (h) and the duration of the forwardthrust:

sÅÅ= h/t (3)

The part of the model below the third level is formedby repeated applications of equations (1)± (3). Forexample, in the fourth level of the model, the velocity ofthe wrist (the distal end-point of the forearm) at releaseis determined by the forearm length, the velocity of the

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Fig. 2. Factors that determine the measured distance of a put. The repeated block applies to the dotted lines below dif-ferent upper body segments. RLS = release, ACC = acceleration, FT = forward thrust, BFT = beginning of forward thrust,ROM = range of motion.

elbow (the proximal end-point of the forearm) and theangular velocity of the forearm at release (equation 1).Applying the repeated block to the dotted lines belowthe box for the angular velocity of the forearm at release(5th level in Fig. 2), the angular velocity of the forearmat release is determined by the angular velocity of theforearm at the beginning of the forward thrust, averageangular acceleration of the forearm during the forwardthrust, and the duration of the forward thrust (equation2). The duration of the forward thrust is determined bythe average angular speed of the forearm during theforward thrust and the range of motion of the forearmduring the forward thrust (equation 3).

Assuming that the angular velocities of the diþ erentsegments at the beginning of the forward thrust arezero, the average angular acceleration of each seg-ment during the forward thrust is directly pro-portional to its angular velocity at release (equation2). The terminal factors (boxes at the ends of thevarious paths) of the model examined in this studycan be categorized into three groups: (1) the kinematiccharacteristics of the shot at the instant of release;(2) the characteristics of diþ erent upper body seg-ments at the instant of release; and (3) the kinematiccharacteristics of diþ erent segments during the forwardthrust.

Shot-putting performed by wheelchair athletes 323

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Data collection

Participants. The participants were 17 males attendinga training camp for elite and emerging wheelchair® eld athletes organized by Wheelchair Sports, USA(Table 1). They all signed informed consent documentsbefore attending the camp. Eight of the participantsrepresented the United States at the 1996 ParalympicGames, ® ve in the shot put, two in both the shotput and pentathlon, and one in the pentathlon. Ofthose who competed in the shot put, two receivedmedals (one gold and one silver), one was placedfourth and one was placed eighth. All but two partici-pants were right-handed. The data for the left-handedparticipants were transposed and were treated asright-handed.

Protocol. Two S-VHS video cameras (Panasonic AG-455, 60 ® elds per second) were used to record the puts.One camera was placed 27 m to the rear of the throwingcircle (rear view) and the other was placed 17 m tothe right-hand side of the circle (side view). The anglebetween the optical axes of the two cameras was approxi-mately 90°. Data were collected in three sessions. Eachparticipant performed six trials with a 2± 3 min restbetween puts. A control object (Peak PerformanceTechnologies, 25 control points, 2.1 ´ 1.9 ´ 1.6 m3), aplumbline and four markers were video-recorded beforeor after a data collection session for spatial reference andde® ning a global reference frame, respectively.

Data reduction

A Peak Motion Measurement System (Peak Per-formance Technologies) was used to extract two-dimensional coordinates from the video recordings.The direct linear transformation (DLT) procedure(Abdel-Aziz and Karara, 1971) was used to obtainthree-dimensional data on the performances of theputters. The calibration errors (i.e. the root-mean-square error between the computed locations of thecontrol points and their known locations) for the threedata collection sessions were 4.19, 5.12 and 6.36 mm,respectively.

The best trial for each putter was selected forsubsequent analysis. For each selected trial, the video-recordings were digitized starting ® ve ® elds beforethe beginning of the forward thrust and ending ® ve® elds after the shot was released. Coordinates of 13body landmarks (vertex, chin± neck intersect, supra-sternal notch, left and right shoulders, elbows, wrists,third knuckles and hips), middle of the front edge ofthe seat, and the centre of the shot were obtained fromeach ® eld. Because the two cameras were not syn-chronized electronically, the instant of release (de® nedas the ® rst ® eld in which the putter lost contact with theshot) was used for synchronization purposes. The rawthree-dimensional data were smoothed using a second-order, low-pass, recursive digital ® lter with a cut-oþfrequency of 7.4 Hz (Yu, 1988). Coordinate transform-ation was performed so that the x-axis was horizontal

Table 1. Putter information

Putterno.

Classi® -cation

Bodymass(kg)

Age(years) Standarda

Personalbestb

(m)

Throwanalysed

(m)

123456789

1011121314151617

F2F2F3F4F4F4F5F5F5F5F5F6F6F7F7F7F8

100.072.795.577.377.5

100.0107.7111.4134.1

97.7127.3

94.554.5

105.988.674.179.5

3125334737224826514620271948304419

EliteEliteEliteEmergingEliteEmergingEliteEmergingEliteEliteEmergingEliteEmergingEliteEmergingEliteEmerging

7.8-5.99.338.09-

10.206.967.76

10.32-8.566.92

10.788.109.80-

5.243.935.237.217.266.519.118.107.468.444.297.086.23

10.138.007.347.98

a Standard rated by Wheelchair Sports, USA.b Best throw recorded in oý cial competitions.

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and pointing towards the front (put direction) and thez-axis was horizontal and pointing to the right of thethrowing circle. The y-axis was pointing vertically up-ward (Fig. 1). In other words, the x-y plane was parallelto a vertical plane that bisected the throwing sector.

To avoid the end-point problems associated with adigital ® lter, the horizontal, vertical and resultantvelocities of the shot at release were determined usingthe un® ltered coordinates of the shot at release andtwo ® elds after release, the known elapse time, andthe equations for uniformly accelerated motion. Thehorizontal velocity is the component of the resultantvelocity in the x-z plane. The angle of release wasdetermined from the horizontal and vertical velocitiesat release. Using the speed (n) and height (h) of release,the optimum angle of release (h) was computed usingthe following equation (Lichtenberg and Wills, 1978):

h = sin - 1 ((2 + 2gh/v2) - 12± ) (4)

where g is the acceleration due to gravity. When theoptimum angles were determined, it was assumed thatthe shot-putters could produce the same speed of releaseregardless of the angle of release. Such an assumptionmay not be valid, because it is likely that the upper armposition relative to the trunk during the forward thrustis not the same for diþ erent angles of release. Con-sequently, diþ erent working ranges of muscle lengthand moment arm of the shoulder muscles for diþ erentarm± trunk positions imply that the resultant shouldertorques produced by the shoulder muscles are not thesame for diþ erent angles of release.

The inclination of a body segment was computed asthe smallest angle between the longitudinal axis of thesegment and the horizontal (x-z) plane. A positiveinclination angle indicates that the distal end-point waslocated above the proximal end-point of the segment.For the trunk segment, the distal and proximal end-points are the mid-shoulders and mid-hips, respectively.

The range of motion of a segment during the forwardthrust was obtained by summing the angles between thesame segment in adjacent ® elds, computed using thedot product, from the beginning of the forward thrust tothe instant of release. The angular speeds of diþ erentupper body segments were computed using the centraldiþ erence method (Wood, 1982). The average angularspeed of a segment during the forward thrust wasdetermined from the range of motion and the durationof the forward thrust (equation 3).

Data analysis

For each parameter, means and standard deviationswere computed for each medical class. Spearman rank-order correlation coeý cients were computed betweenselected parameters and the measured distance, andbetween selected parameters and the medical classi-® cation. Correlation coeý cients of |r| ³ 0.490 and|r| ³ 0.645 were required to attain statistical signi® -cance at the 0.05 and 0.01 levels of probability, respect-ively (n = 17).

Results

Kinematic characteristics of the shot at release

The average speeds and angles of release for diþ erentclasses were 5.3± 7.8 m ´s- 1 and 21.2± 34.3°, respectively(Table 2). Of the puts analysed, all but one had anglesof release smaller than the optimum angle of release. Allparticipants in this study released the shot in front of theanterior edge of the seat (Table 3). Because all putterspositioned their chairs at the front end of the circle,the gain in distance at release means that the measureddistance is greater than the ¯ ight distance of the shot.

In most trials, the shot was located directly in frontof (or slightly oþ to the right) and above the right

Table 2. Selected characteristics of the shot at the instant of release (mean ± s)

Classi® cation

F2(n = 2)

F3(n = 1)

F4(n = 3)

F5(n = 5)

F6(n = 2)

F7(n = 3)

F8(n = 1)

Speed of release (m´s - 1)horizontalverticalresultant

4.8 ± 0.12.0 ± 1.55.3 ± 0.6

5.6 ± 0.02.2 ± 0.06.0 ± 0.0

6.0 ± 0.23.6 ± 0.36.9 ± 0.3

6.5 ± 1.03.5 ± 1.07.4 ± 1.2

6.6 ± 0.13.2 ± 1.27.4 ± 0.5

6.4 ± 1.14.3 ± 0.47.8 ± 1.1

6.4 ± 0.03.9 ± 0.07.5 ± 0.0

Angle of release (°)Optimum angle (°)Angle diþ erence (°) a

19.8 ± 13.733.3 ± 2.3

- 13.5 ± 11.3

22.2 ± 0.033.8 ± 0.0

- 11.6 ± 0.0

29.8 ± 2.336.3 ± 0.6- 6.5 ± 1.8

27.1 ± 6.636.7 ± 1.8- 9.6 ± 6.5

23.8 ± 6.836.9 ± 0.7

- 13.1 ± 6.1

33.7 ± 2.136.9 ± 1.5- 3.2 ± 3.6

29.3 ± 0.036.7 ± 0.0- 7.4 ± 0.0

a A negative value indicates that the angle of release is smaller than the optimal angle.

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shoulders at the instant of release (Table 3). The rightshoulder was higher than, and to the right of, the leftshoulder at the instant of release. However, the relativelocations of the two shoulders in the forward directionwere not consistent. The right shoulder was locatedbehind the left shoulder at the instant of release in47% of the trials. Instead of using the axial rotation(twisting) of the trunk, some wheelchair athletes placemuch emphasis on lateral rotation of the trunk duringthe forward thrust. As a result, the right shoulder waslocated behind the left shoulder at the instant of release.

At the instant of release, the trunk was not in an up-right position (Table 4). The inclination of the shoulder

girdle indicated that the right shoulder was higher thanthe left shoulder at the instant of release. The diþ erencein shoulder heights can be estimated from the resultsshown in Table 3. The diþ erence in the inclinations ofthe forearm and upper arm at release indicates that theshot was released before the arm was fully extended.

In general, the angular speeds at release for dif-ferent segments increased with decreasing level ofspinal cord injury. At the instant of release, the upperarm had the highest angular speed among diþ erentsegments in 12 of 17 trials analysed. To perform aneþ ective putting action, a shot-putter usually keeps theelbow of his throwing arm away from his trunk, and

Table 3. Shot location at the instant of release (mean ± s)

Classi® cation

F2(n = 2)

F3(n = 1)

F4(n = 3)

F5(n = 5)

F6(n = 2)

F7(n = 3)

F8(n = 1)

Height above ground (m)Forward location relativeto seat front (m)

1.86 ± 0.140.36 ± 0.22

2.24 ± 0.000.40 ± 0.00

2.10 ± 0.110.17 ± 0.05

2.18 ± 0.220.45 ± 0.19

2.15 ± 0.010.38 ± 0.01

2.32 ± 0.080.27 ± 0.03

2.33 ± 0.000.53 ± 0.00

Location relative to right shoulder (m)forwardverticallateral

0.57 ± 0.030.65 ± 0.10

- 0.01 ± 0.07

0.40 ± 0.000.73 ± 0.000.01 ± 0.00

0.35 ± 0.050.82 ± 0.030.08 ± 0.05

0.44 ± 0.150.77 ± 0.070.01 ± 0.11

0.46 ± 0.000.77 ± 0.080.13 ± 0.16

0.38 ± 0.050.82 ± 0.030.07 ± 0.09

0.41 ± 0.000.80 ± 0.000.11 ± 0.00

Location relative to left shoulder (m)forwardverticallateral

0.62 ± 0.170.75 ± 0.270.30 ± 0.08

0.46 ± 0.000.93 ± 0.000.34 ± 0.00

0.21 ± 0.150.94 ± 0.100.43 ± 0.10

0.45 ± 0.071.03 ± 0.160.29 ± 0.15

0.51 ± 0.010.95 ± 0.170.46 ± 0.14

0.44 ± 0.141.00 ± 0.040.44 ± 0.06

0.69 ± 0.001.11 ± 0.000.32 ± 0.00

Note: A positive value indicates that the shot was located in front of, above, or to the right of the reference location.

Table 4. Body segment kinematics at the instant of release (mean ± s)

Classi® cation

F2(n = 2)

F3(n = 1)

F4(n = 3)

F5(n = 5)

F6(n = 2)

F7(n = 3)

F8(n = 1)

Segment inclination (°) a

trunkshoulder girdleupper armforearmhand

71.1 ± 17.014.9 ± 24.814.9 ± 17.637.9 ± 4.255.4 ± 25.2

70.2 ± 0.029.9 ± 0.026.2 ± 0.055.8 ± 0.076.6 ± 0.0

68.0 ± 12.717.4 ± 11.332.1 ± 6.559.3 ± 5.864.1 ± 5.1

58.3 ± 14.038.0 ± 15.229.3 ± 4.046.8 ± 12.158.3 ± 14.9

72.5 ± 6.028.2 ± 12.935.3 ± 9.744.8 ± 7.738.6 ± 23.7

73.2 ± 8.125.4 ± 3.040.0 ± 5.352.1 ± 7.168.9 ± 10.3

65.6 ± 0.041.7 ± 0.033.6 ± 0.052.2 ± 0.063.7 ± 0.0

Angular speed (rad ´s - 1)trunkshoulder girdleupper armforearmhand

1.59 ± 0.314.37 ± 0.756.81 ± 1.365.04 ± 2.491.58 ± 0.92

3.51 ± 0.003.58 ± 0.006.79 ± 0.009.97 ± 0.002.01 ± 0.00

0.94 ± 0.373.33 ± 1.568.39 ± 1.157.39 ± 2.891.64 ± 0.84

2.35 ± 1.036.73 ± 2.909.04 ± 2.006.51 ± 1.802.11 ± 0.47

2.25 ± 0.585.90 ± 3.696.23 ± 4.614.44 ± 0.211.57 ± 0.71

2.23 ± 0.397.19 ± 2.85

14.22 ± 0.545.02 ± 1.692.42 ± 0.93

2.09 ± 0.007.79 ± 0.00

13.99 ± 0.003.69 ± 0.002.60 ± 0.00

a A positive value indicates that the distal end-point was located above the proximal end-point of the segment.

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both the upper arm and shoulder girdle move inapproximately the same plane of motion during thedelivery. Therefore, the diþ erence in angular speedsof the upper arm and shoulder girdle provides a roughestimate of the shoulder horizontal adduction speed.Because the upper arm and forearm were moving inopposite angular directions, the sum of the angularspeeds of these two segments provides an estimate ofthe speed of elbow extension. It is obvious that elbowextension contributes to the speed of the shot muchmore than the motions of the other joints.

The segment range of motion data reveal that thegreatest range of motion was in the upper arm in allbut two trials. In these two trials, the shoulder girdlehad a slightly greater range of motion than the upperarm. The hand range of motion was the smallest in alltrials (Table 5). In most trials, the trunk moved forward(positive x-direction) and sideways towards the left sideof the circle (negative z-direction) during the forwardthrust. Although the angular speeds of diþ erent seg-ments generally increased with increasing class number,the ranges of increase for the shoulder girdle, upper armand forearm were much greater than the ranges ofincrease for the trunk and hand (Table 5). The greatestaverage angular speed was in the upper arm in all buttwo trials. Apparently, the upper arm motion is veryimportant for determining the outcome of a shot-putperformance.

Correlation coeý cients

A signi® cant positive correlation was found betweenclassi® cation and measured distance (r = 0.58, P < 0.05).The correlation coeý cients between selected para-

meters and the classi® cation, and between selectedmeasures and measured distance, are presented inTable 6.

The height of release was signi® cantly correlatedwith both the classi® cation and measured distance(r = 0.62 and 0.79, respectively). The angle of releaseand vertical location of the shot relative to the rightshoulder at release were signi® cantly correlated withthe measured distance (r = 0.55 and 0.49, respectively)but not to the classi® cation. The vertical location ofthe shot relative to both shoulders at release was sig-ni® cantly correlated with both the classi® cation andmeasured distance (r = 0.51± 0.63, P < 0.01). Onereason why athletes of a higher class had greater releaseheights was because they could drop the left shouldermore and elevate the right shoulder more than athletesof a lower class.

The inclination of the upper arm at release wassigni® cantly correlated with the classi® cation (r = 0.57,P < 0.05) but not the measured distance. The angularspeed of the upper arm at release was signi® cantlycorrelated with both the classi® cation and measureddistance (r ³ 0.64, P < 0.01). The angular speed ofthe hand at release was signi® cantly correlated withthe measured distance (r = 0.50, P < 0.05) but not theclassi® cation. Although the contribution of handmotion (or wrist ¯ exion) is limited by its short segmentlength (equation 1), the eþ ort required to increase handspeed should not be overlooked.

Of the segmental ranges of motion examined in thisstudy, only that of the shoulder girdle was signi® cantlyrelated to both the classi® cation and the measureddistance (r ³ 0.53, P < 0.05). The only other signi® -cant correlation was between the upper arm range of

Table 5. Body segment range of motion and average angular speed during the forward thrust (mean ± s)

Classi® cation

F2(n = 2)

F3(n = 1)

F4(n = 3)

F5(n = 5)

F6(n = 2)

F7(n = 3)

F8(n = 1)

Segment range of motion (°)trunkshoulder girdleupper armforearmhand

37.8 ± 13.094.7 ± 22.6

125.2 ± 22.967.2 ± 14.827.8 ± 14.1

53.6 ± 0.0153.0 ± 0.0151.9 ± 0.0

94.7 ± 0.038.0 ± 0.0

46.8 ± 18.378.0 ± 14.5

144.1 ± 20.996.2 ± 45.925.0 ± 12.9

55.4 ± 18.2125.4 ± 40.9155.9 ± 21.3

88.1 ± 20.636.7 ± 12.3

52.6 ± 1.3121.0 ± 37.3152.0 ± 23.9

83.6 ± 15.133.0 ± 12.2

50.3 ± 11.5151.9 ± 30.2172.1 ± 10.1

90.8 ± 26.431.7 ± 11.7

37.3 ± 0.0178.7 ± 0.0187.3 ± 0.090.4 ± 0.036.5 ± 0.0

Average angular speed (rad ´s- 1)trunkshoulder girdleupper armforearmhand

1.39 ± 0.283.52 ± 0.314.67 ± 0.152.50 ± 0.181.09 ± 0.69

1.75 ± 0.005.01 ± 0.004.97 ± 0.003.10 ± 0.001.24 ± 0.00

1.83 ± 0.323.29 ± 0.906.01 ± 1.223.73 ± 1.130.95 ± 0.30

2.20 ± 0.735.09 ± 1.786.26 ± 1.023.49 ± 0.611.44 ± 0.39

2.14 ± 0.295.06 ± 2.326.28 ± 1.993.46 ± 1.171.30 ± 0.28

2.19 ± 0.376.62 ± 1.097.54 ± 0.383.91 ± 0.681.42 ± 0.64

2.44 ± 0.0011.69 ± 0.0012.25 ± 0.005.91 ± 0.002.39 ± 0.00

Shot-putting performed by wheelchair athletes 327

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motion and the classi® cation (r = 0.64, P < 0.01). Ofthe segmental average angular speeds identi® ed in themechanical model shown in Fig. 2, all but the averageangular speed of the hand were signi® cantly correlatedwith the classi® cation (r ³ 0.53, P < 0.05), and all butthe average angular speeds of the forearm and handyielded signi® cant correlations with the measureddistance (r ³ 0.57, P < 0.05).

Discussion

Limitations

There are several possible sources of error in thekinematic measurements obtained in this study. Inaddition to possible errors resulting from manualdigitizing and limited resolution of the video images,the cameras were not synchronized ± that is, theywere not gen-locked. The error associated with the useof critical instants to synchronize two sets of videorecordings is generally small (Yeadon, 1989) andshould not aþ ect the main ® ndings. The correlationcoeý cients presented in Table 6 serve to provide anoverview of the inter-relationships among the measureddistance, classi® cation and various variables. Thesigni® cant correlations should be interpreted withcaution because of the potential errors associated withmultiple tests.

Kinematic characteristics

As expected, the speeds of release (Table 2) were smallerthan those reported for puts performed by male able-bodied athletes: 11.4 m´s - 1 (Dessureault, 1977), 13.2m ´s- 1 (McCoy et al., 1984) and 10.6 m ´s- 1 (Alexanderet al., 1996). It would appear that the advantage towheelchair athletes of using lighter shots is not enoughto oþ set the disadvantages of the lack of leg motion inshot-putting. The angles of release were also smallerthan those performed by male able-bodied putters:36.8° (Dessureault, 1977), 37.2° (McCoy et al., 1984)and 36.3° (Alexander et al., 1996). The angles of releaseobserved in this study were smaller than the theoreticaloptimum for a projectile; similar ® ndings have beenreported for able-bodied putters (Dessureault, 1977;McCoy et al., 1984; Alexander et al., 1996).

According to competition rules, the seat of anathlete’ s chair ± including the cushion ± for ® eld eventsmust not exceed 75 cm in height (National WheelchairAthletics Association, 1992). For wheelchair athletes,the chair design is important because it may help orhinder the performance depending on how well it ® tsthe putter’ s ability. As a result, athletes use chairs ofdiþ erent seat heights to optimize their performance.

The heights of release found in F2 subjects (Table 3)were much smaller than those found in male elite able-bodied putters: 2.03 m (Dessureault, 1977), 2.28 m(McCoy et al., 1984) and 2.13 m (Alexander et al.,1996). Although the height of release is relatively lessimportant than the speed and angle of release, if allelse is equal, a putter who has a higher sitting height andlonger arms will have a higher release height and anadvantage over putters with lower release heights.

Table 6. Spearman rank-order correlation coeý cients

VariableClassi® -cation

Measureddistance

Shot at release

Angle of releaseHeight of releaseForward location relative to seat

frontLocation relative to right shoulder

forwardverticallateral

Location relative to left shoulderforwardverticallateral

0.350.62**

0.22

- 0.100.320.28

0.120.430.24

0.52*

0.79***

0.10

- 0.420.49*

0.26

0.030.64**

0.10

Body segment at release

Inclinationtrunkshoulder girdleupper armforearmhand

Angular speedtrunkshoulder girdleupper armforearmhand

0.070.260.57*

0.02- 0.03

0.420.470.64**

- 0.390.36

- 0.040.390.220.430.08

0.180.480.76***

- 0.080.50*

Range of motion during the delivery

TrunkShoulder girdleUpper armForearmHand

0.060.53*

0.64**

0.110.18

0.300.55*

0.410.070.19

Average angular speed during the delivery

TrunkShoulder girdleUpper armForearmHand

0.66**

0.66**

0.75***

0.53*

0.38

0.57*

0.69**

0.61**

0.460.37

Signi® cant at: *P < 0.05; **P < 0.01; ***P < 0.001.

328 Chow et al.

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The trunk positions at the instant of shot release forwheelchair putters are diþ erent from those exhibitedby able-bodied putters. An examination of the trunkorientation in the y-z plane revealed that the trunk wasdeviated to the putter’ s left side except in two partici-pants. On average, the angular location of the trunk inthe x-y plane (the angle measured from the positivex-axis in the counter-clockwise direction) was 75.8°(s = 13.8°); this is smaller than the correspondingvalues of 93.9° (male) and 110.4° (female) reported byAlexander et al. (1996). It is probable that the wheel-chair putters can lean forward at release because theydo not have to worry about falling out of the circle(Fig. 1a).

Based on the results of segmental angular kine-matics (Tables 4 and 5), the only F3 putter in this studyseemed to be more functional in his upper body thanthe F4 putters, even after taking into account the dif-ference in the weight of shot used by athletes of thesetwo classes. Despite experiencing diý culty in holdingthe shot (no full ® nger function), this putter had goodsitting balance compared with the other quadriplegicputters. This suggests that trunk mobility might be moreimportant than hand function in the classi® cationprocess.

It is not easy interpreting the average angular speedof the forearm during the forward thrust (Table 4)because this segment does not move in the samerotation direction during the forward thrust. From anoverhead view of the trunk, the forearm rotates in thecounter-clockwise direction at the beginning of theforward thrust and rotates in the clockwise directiontowards the end of this phase. A similar analysis can beapplied to the hand segment.

Correlation coeý cients

The signi® cant positive correlations between theheight of release and the classi® cation suggest that thegreater heights of release contributed to the greaterput distances attained by athletes of higher class.Both the vertical locations of the shot relative to theright and left shoulders were signi® cantly correlatedwith the measured distance but not the classi® cation(Table 6). This suggests that the variation in theseparameters was primarily due to diþ erences in tech-nique, not the functional capability of the athletes.This also reinforces the importance of achieving greaterheight of release.

The signi® cant correlations between the angularspeed of the upper arm at release and both the classi® -cation and measured distance (Table 6) suggest thatthe angular speed of the upper arm at release is adiscriminating factor in diþ erentiating the functionaldiþ erences among wheelchair athletes. The signi® cant

correlations between average angular speeds of thetrunk and shoulder girdle during the forward thrust andboth the classi® cation and measured distance seem tosuggest that, in addition to the upper arm, the trunkand shoulder girdle motions play a role in determiningthe variation in measured distance. Overall, the highcorrelations for the average angular speeds of upperbody segments (Table 6) indicate the importance ofachieving a high average angular speed for each upperbody segment during the delivery.

Conclusions

The present study is the ® rst attempt to describe thekinematic characteristics of shot-putting performed bywheelchair athletes. More quantitative data, especiallythose collected during major competitions, are neededfor the development of a database on performancecharacteristics. Despite using lighter shots, the speeds ofrelease attained by wheelchair putters are much smallerthat those exhibited by elite male able-bodied putters.The low angles of release found in wheelchair puttersare probably related to the forward lean trunk positionat release. The results of the correlation analysis suggestthat the angular speed of the upper arm at release is adiscriminating factor in diþ erentiating the functionaldiþ erences among wheelchair athletes. We recommendthat wheelchair putters should strive to increase theangle and height of release as long as the speed of releaseis not compromised.

Acknowledgements

We would like to thank Randy Frommater, Todd Hat® eld,Tim Millikan and Marty Morse for their assistance in datacollection. This study was supported in part by WheelchairSports, USA and the National Association for Sport andPhysical Education.

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Appendix: Medical classi® cations for wheelchair ® eld athletes

ClassInjurylevel Functional capability Anatomical capability

F2 C7 Unable to form a ® st and therefore do not usuallyhave ® nger contact with the shot at the release point.Unable to spread ® ngers apart

Have functional elbow ¯ exors and extensors, wristdorsi¯ exors and palmar ¯ exors. Have good shoulder musclefunction. May have some ® nger ̄ exion and extension, butnot functional

F3 C8 Can spread the ® ngers apart but not with normalpower. Use some spreading of the ® ngers, and can`grasp’ the shot-put when throwing

Have full power elbow and wrist joints. Have full or almostfull power of ® nger ̄ exion and extension. Have functionalbut not normal intrinsic muscles of the hand

F4 T1± T7 Have no sitting balance. Usually hold on to chairwhile throwing

No functional trunk movement, otherwise same as F3

F5 T8± L1 Have movement in backward and forward plane andsome trunk rotation. Have fair to good sitting balanceand no functional hip ¯ exors

Normal upper limb function. Have abdominal muscles andspinal extensor. May have non-functional hip ¯ exors. Haveno adductor function

F6 L2± L5 Have good balance and movements backward andforward. Have good trunk rotation. Hip ¯ exion andhip adduction are present

May have some knee extension and knee ̄ exion. Bilateralhigh thigh amputations

F7 S1± S2 Have good balance and movements backward andforward. Usually have very good side-to-sidemovements

Usually can bend one hip backward and one ankledownward. One side of body is usually stronger.Above-knee amputations

F8 Minimum disability, almost fully functional Amputee: either bilateral above-knee or single highabove-knee. Polio: with one good leg, or bilateral goodbuttock

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