CHOW, J. W.; MINDOCK, L. A. Discus throwing performances and medical classification of wheelchair athletes. Medicine and Science in Sports and Exercise, v. 31, n. 9, p. 1272-1279, 1999.

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AUTHOR: JOHN W. CHOW; LAURA A. MINDOCK
TITLE: Discus throwing performances and medical classification of wheelchair athletes
SOURCE: Medicine and Science in Sports and Exercise 31 no9 1272-9 S 1999
The magazine publisher is the copyright holder of this article and it is reproduced with permission. Further reproduction
of this article in violation of the copyright is prohibited.
ABSTRACT
CHOW, J. W. and L. A. MINDOCK. Discus throwing performances and medical classification of wheelchair athletes. Med.
Sci. Sports Exerc., Vol. 31, No. 9, pp. 1272-1279, 1999. Purpose: The purpose of this study was to identify those
kinematic characteristics that are most closely related to the medical classification and measured distance of a throw.
Methods: Two S-VHS camcorders (60 fields?s[sup-1]) were used to record the performance of 14 males of different
classes. Each subject performed 10 trials and the best two trials from each subject were selected for analysis. Three-
dimensional kinematics of the discus and upper body segments at the instant of release and the range of motion and
average angular speed of different segments during the final forward swing were determined. Results: The speeds of the
discus at a release, ranging from 9.9 to 17.2 m?s[sup-1], were smaller than those exhibited by elite male able-bodied
throwers. However, the angles of release, ranging from 24.6 to 41.4°, were comparable with those observed in
able-bodied throwers. Of the segmental kinematic parameters, (a) the inclination and angular speed of the upper arm at
release; (b) the ranges of motion of the shoulder girdle, upper arm, and forearm during the forward swing; and (c) the
average angular speed of the shoulder girdle during the forward swing were significantly correlated to both the
classification and measured distance. The inclinations of different segments at the instant of release suggested that
athletes with high level of spinal cord injury emphasized the elbow flexion to compensate for the deficiency in shoulder
girdle movement. Conclusions: In addition to the speed of the discus at release, the shoulder girdle movement during
the forward swing is an important determinant of classification and measured distance.
Key Words: KINEMATICS, BIOMECHANICS, DISABILITY, ATHLETICS
Opportunities for sports competition among wheelchair athletes (primarily those with spinal cord injury, spina bifida,
amputation, and some mobility-impaired congenital defects) have increased steadily in the last few decades. Track and
field events are official events of the Paralympic Games and are popular among wheelchair athletes. Previous studies
have focused on the propulsion of racing wheelchairs. The field events, such as shot put, discus and javelin throws, have
not been investigated. Baseline data are needed for teaching and instruction purposes and to build the foundation for
future research activities in these areas.
Competitors in wheelchair athletics are classified based on the level of spinal cord injury and the control and strength
of different muscle groups (2) (see Appendix). For the field events there are eight different classes, F1-F8 (neurologic
levels C6-S2). All athletes except those in class F8 throw a 1.0-kg discus. The F8 athlete throws a 1.5-kg discus.
Athletes perform throws from custom-made chairs (Fig. 1) that are anchored to the throwing circle by cables. They
design their chairs and adopt sitting positions that suit their muscle function and strength, flexibility, and personal
preference.
The discus throw involves primarily rotational motion. For able-bodied athletes, the leg strength plays an important
role in determining the outcome of the throw. Most wheelchair athletes have little or no use of their lower extremities,
yet they must apply the same biomechanical principles as the able-bodied throwers. Because of the differences in
disability, chair designs, and sitting positions, athletes may use a variety of throwing techniques.
The purposes of this study were to identify those kinematic characteristics that are most closely related to the
medical classification and measured distance of a throw.
METHODS
THEORETICAL MODEL
Because the thrower sits on a chair throughout the throwing action, motion at the hips is minimal even for those who
have partial functions in the lower extremities. For the purpose of analysis, five linked segments can be identified
between the hips and the discus (Fig. 1B): the trunk (from mid-hips to mid-shoulders), the shoulder girdle (from
mid-shoulders to throwing shoulder), the upper arm (from shoulder to elbow), the forearm (from elbow to wrist), and
the hand (from wrist to center of the discus). During the throw, the kinematics of the discus is determined by the
angular kinematics of these five segments (Fig. 2). Although some subjects performed one or more preliminary swings
before the forward swing before release, this study focused on the kinematic characteristics of the last forward swing
and the release of the discus.
Figure 2 presents a discus throw model showing the factors that determine the measured distance of a throw. In the
second level of the model, a thrower will lose distance if the discus is released inside the throwing circle and vice versa.
In the third level, the flight distance is determined by factors governing the trajectory of a projectile. For the rest of the
model, consider the angular motion of a body segment, the velocity of the distal endpoint of the segment (v[subd]) is
determined by the velocity of the proximal endpoint of the segment (v[subp]), the angular velocity of the segment
(omega), and the length of the segment (l):
v[subd] = omegal + v[subp] [1]
During the forward swing before the discus is released, the average angular acceleration of a segment (alpha) is
given by:
alpha = (omega[subR] - omega[subB])/t [2]
where omega[subB] and omega[subR] are the angular velocities of the segment at the beginning of the forward
swing and at release, respectively, and t is the time taken to complete the forward swing. The average angular speed of
a segment during the forward swing (sigma) is determined using the angular distance the segment traveled during the
forward swing (ø) and the duration of the forward swing:
sigma = ø/t [3]
The part of the model below the third level is formed by repeated applications of equations 1-3. For example, in the
fourth level of the model, the velocity of the wrist (the distal endpoint of the forearm) at release is determined by the
forearm length, the velocity of the elbow (the proximal endpoint of the forearm), and the angular velocity of the forearm
at release (eq. 1). Applying the repeated block to the dotted lines below the box for the angular velocity of the forearm
at release (5th level in Fig. 2), the angular velocity of the forearm at release is determined by the angular velocity of the
forearm at the beginning of the forward swing, average angular acceleration of the forearm during the forward swing,
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and the duration of the forward swing (eq. 2). The duration of the forward swing is determined by the average angular
speed of the forearm during the forward swing and the range of motion of the forearm during the forward swing (eq. 3).
Assuming that the angular velocities of the different segments at the beginning of the forward swing are zero, the
average angular acceleration of each segment during the forward swing is directly proportional to its angular velocity at
release (eq. 2). The terminal factors (boxes at the ends of the various paths) of the model examined in this study could
be categorized into three groups: 1) the kinematic characteristics of the discus at the instant of release, 2) the
characteristics of different upper body segments at the instant of release, and 3) the kinematic characteristics of
different segments during the forward swing.
DATA COLLECTION
Subjects. The subjects were the 17 male participants of a training camp held at the USOC Training Center in San
Diego in March 1996 for elite and emerging wheelchair field athletes organized by the Wheelchair Sports, USA (Table 1).
The subjects signed informed consent documents before attending the camp. Seven subjects represented the United
States at the 1996 Paralympic Games, four in the discus throw and three in the pentathlon, and all four discus
competitors received medals (one gold, one silver, and two bronzes). All but two subjects were right-handed. The data
for the left-handed subjects were transposed and were treated as right-handed.
Protocol. Two S-VHS video cameras (Panasonic, Secaucus, NJ, AG-455, 60 fields?s[sup-1]) were used to record the
throws. One camera was placed 10 m to the rear of the throwing circle (rear view) and the other was placed 18 m to the
right-hand side of the circle (side view). The angle between the optical axes of the two cameras was approximately 90°.
Data were collected in two sessions. Each subject performed 10 trials with a 2- to 3-min rest between throws. A control
object (Peak Performance Technologies (Englewood, CO), 25 control points, 2.1 × 1.9 × 1.6 m[sup3]), a plumbline, and
four markers were videorecorded before or after a data collection session for spatial reference and for defining a global
reference frame, respectively.
DATA REDUCTION
A Peak Motion Measurement System (Peak Performance Technologies) was used to extract two-dimensional
coordinates from the video recordings. The direct linear transformation procedure (1) was used to obtain three-
dimensional (3D) data on the performances of the subjects. The calibration errors (i.e., the root-mean-square error
between the computed locations of the control points and their known locations) for the two data collection sessions
were 6.70 and 6.19 mm, respectively.
The best two legal trials for each subject were selected for subsequent analysis. However, only one trial was available
from one subject. For each selected trial, the video recordings were digitized starting five fields before the beginning of
the forward swing and ending five fields after the discus was released. Coordinates of 13 body landmarks (vertex,
chin-neck intersect, suprasternal notch, left and right shoulders, elbows, wrists, third knuckles, and hips), middle of the
front edge of the seat, and two landmarks on the discus (anterior and posterior ends, Fig. 1A) were obtained from each
field. Because the two cameras were not synchronized electronically, the instant of release (defined as the first field in
which the subject lost contact with the discus) was used for synchronization purposes. The raw 3D data were smoothed
using a second-order, lowpass, recursive digital filter with a cut off frequency of 7.4 Hz. Coordinate transformation was
performed so that the x-axis was horizontal and pointing toward the front (throw direction) and the z-axis was
horizontal and pointing to the right of the throwing circle. The y-axis was pointing vertically upward (Fig. 1), that is, the
x-y plane was parallel to a vertical plane that bisected the throwing sector.
The center of gravity of the discus was computed as the midpoint between the anterior and posterior ends of the
discus. The horizontal, vertical, and resultant velocities of the discus at release were determined using the locations of
the discus at release and two fields after release, the known elapse time, and the equations for uniformly accelerated
motion. The angle of release was determined from the horizontal and vertical velocities at release. The inclination of a
body segment was computed as the smallest angle between the longitudinal axis of the segment and the horizontal
(x-z) plane. A positive inclination angle indicates that the distal endpoint was located above the proximal endpoint of
the segment. For the trunk segment, the distal and proximal endpoints are the mid-shoulders and mid-hips,
respectively.
The range of motion (ROM) of a segment during the forward swing was obtained by summing the angles between the
same segment in adjacent fields, computed using the dot product, from the beginning of the forward swing to the
instant of release. The angular speeds of different upper body segments were computed using the central differences
method (12). The average angular speed of a segment during the forward swing was determined from the ROM and the
duration of the forward swing (eq. 3).
DATA ANALYSIS
For each parameter, means and SD were computed for each medical class. Pearson product moment coefficients of
correlation were computed between selected paramenters and the measured distance, and between selected
paramenters and the medical classification. Correlation coefficients of |r| [greater or equal] 0.45 and |r| [greater or
equal] 0.55 were required to attain statistical significance at the 0.01 and 0.001 levels of probability, respectively (N =
33, df = 31). A power of 55% for each test (r = 0.45, N = 33, and 0.01 level) was deemed acceptable for the purpose of
this study (6).
RESULTS AND DISCUSSION
DESCRIPTIVE DATA
To get an idea of the quality of the throws analyzed in this study, the measured distances (Table 1) were compared
with the 1996 Paralympic medalists' performance and are presented in Figure 3. Although the throws analyzed in this
study were not world class, they represented high level performance and the performance was considered adequate for
this study.
Kinematic characteristics of the discus at release. As expected, the speeds of release found in this study, ranging
from 9.9 to 17.2 m?s[sup-1], were smaller than those reported for throws performed by elite male able-bodied athletes:
24.0-25.3 m?s[sup-1] (4), 21.7-25.4 m?s[sup-1] (5), and 24.2-27.3 m?s[sup-1] (10). The greatest speed of release
recorded in this study (17.2 m?s[sup-1]) came from a throw by an elite F5 subject. The distance of this throw (24.76
m) was not great given the fast speed at release. The short distance of the throw may have been a result of a small
angle of release (27.8°--the second smallest recorded in this study).
The angle of release ranged from 24.6 to 41.4° (Table 2). These values were generally similar to those performed by
able-bodied throwers (4,5,10). Assuming that the attitude angle (inclination of the discus) was constant during the
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flight and using computer simulation techniques, Cooper et al. (3) concluded that a greater angle of release (i.e.,
40-45°) is optimum for throwers of lesser ability (i.e., throws with speed of release approximately equal to 18.3
m?s[sup-1]). However, these suggested optimum angles were not observed in this study.
In official competitions, the seat of a chair for field events including the cushion must not exceed 75 cm in height (8).
The chair design is important because it may help or hinder the athlete depending on how well it fits the thrower's
disability. As a result, it is not uncommon for a thrower to use a chair with a seat lower than the maximum allowable
height, especially those who use the semi-forward sitting position (Fig. 1B). Because of the limitation on seat height,
the heights of release (Table 3) were lower than those found in male elite able-bodied throwers (4,5). Although the
height of release is relatively less important compared with the speed and angle of release, if all else is equal, a thrower
who has a higher sitting height and long arms will have a higher release height and an advantage over throwers with
lower release heights.
In most of the throws performed by elite able-bodied throwers, the discus is inside the circle at the instant of release
(5). This is not true for wheelchair throwers. All the subjects in this study could release the discus in front of the anterior
edge of the seat (Table 3). Because all throwers positioned their chairs at the front end of the circle, the gain in distance
at release means that the measured distance is greater than the flight distance of the discus. In every throw analyzed in
this study, the discus was located in front of, above, and to the right of both shoulders at the instant of release (Table
3). Corresponding data for able-bodied throwers have not been reported in the literature. The forward locations of the
discus relative to both shoulders reviewed showed that the left shoulder was slightly in front of the right shoulder at the
instant of release in some of the throws analyzed. To those subjects who had their hips facing sideward during the
throws (Fig. 1B), the sitting position limited the shoulder rotation at the end of the forward swing.
Segment kinematic characteristics at release. At the instant of release, the trunk was not in an upright position
(Table 4). An examination of the trunk orientation in the y-z plane revealed that the trunk was deviated to the thrower's
left side except in three subjects. On average, the angular location of the trunk in the x-y plane (the angle measured
from the positive x-axis in the counterclockwise direction) was 90.6 +/- 13.0°. This average value is smaller than the
corresponding value of 97.5 +/- 4.2° reported by Gregor et al. (4) and 95.7 +/- 6.8° by McCoy et al. (7). In other
words, most of the elite able-bodied throwers leaned slightly backward at the instant of release. The inclination of the
shoulder girdle (Table 4) indicated that the right shoulder was higher than the left shoulder at the instant of release.
The difference in shoulder heights can be estimated from data shown in Table 3. The upper arm was at a near horizontal
position for F5-F8 subjects and below the shoulder level for the F2-F4 subjects at the instant of release. Except in one
subject, the forearm was above the elbow level at the instant of release. Based on the arm positions at the instant of
release, it seems that subjects with high level spinal cord injury tend to include elbow flexion in their throwing actions.
At the instant of release, the distal segments moved faster than the proximal segments (Table 4). The differences in
angular speeds of adjacent segments provide estimates of the shoulder horizontal adduction (motion of the upper arm
relative to the shoulder girdle) and elbow flexion (forearm relative to upper arm) speeds. The shoulder horizontal
adduction speed was greater than the elbow flexion speed in subjects of low level spinal cord injury (F5-F8). This
implies that the upper arm movement contributes more to the speed of release of the discus compared with the forearm
movement. On the other hand, elbow flexion seems to be as important as the shoulder horizontal adduction in
determining the speed of release of the discus in the F2-F4 subjects.
Segment kinematic characteristics during the forward swing. In general, the distal segments had greater ROM than
the proximal segments (Table 5). In most trials, the trunk moved forward (positive x direction) and sideward toward the
left side of the circle (negative z direction) during the forward swing. The ROM of the trunk in the x-y and y-z planes
were 18.0 +/- 13.3° and 10.3 +/- 7.5°, respectively. All F2 and F4 subjects had limited shoulder girdle ROM. The only
F3 subject in this study had shoulder girdle ROM comparable with F5-F7 subjects. In spite of having difficult in grasping
the discus (no full finger function), this subject had good sitting balance compared with the F2 and F4 subjects. The
difference in upper arm and forearm ROM is another indication of elbow flexion occurred during the forward swing.
The average angular speed of the trunk was relatively small compared with those exhibited by the other segments
(Table 5). Apparently, F5-F8 subjects had advantage over F2-F4 subjects in the average angular speed of the shoulder
girdle. However, on average, the F2 and F4 subjects had greater average angular speed of the forearm than the subjects
in the other classes. It seems that the F2 and F4 subjects emphasized the elbow flexion to compensate for the
deficiency in shoulder girdle movement. Compared with the same parameter in the other segments, the average angular
speeds of the upper arm were relatively consistent across different classes.
CORRELATION COEFFICIENTS
A significant positive correlation was found between classification and measured distance (r = 0.76, P < 0.001). The
strength of this correlation is not as strong as the one between classification and 1996 Paralympic medalists'
performance (Fig. 3). The correlation coefficients between selected parameters and the classification and the measured
distance are presented in Table 6.
Kinematic characteristics of the discus at release. The horizontal, vertical, and resultant velocities of the discus at
release were significantly correlated to both the classification and measured distance. The high correlation coefficients,
ranging from r = 0.55 to r = 0.84, P < 0.001, indicate that the speed of release is a major determinant of the variation
in measured distance observed in this study and is highly correlated to the classification. The correlation coefficient
between the speed of release and measured distance (r = 0.84, P < 0.001) is the largest coefficient found in this study.
This value is comparable to the corresponding values reported in the literature: r = 0.74 from 14 male elite able-bodied
athletes and r = 0.91 from 15 female elite able-bodied athletes (5) and r = 0.87 from eight male elite able-bodied
athletes (9). Because the speed of release is determined by the motions of the upper body segments during the forward
swing (Fig. 2), the high correlation between the speed of release and classification (r = 0.77, P < 0.001) signifies the
overall fairness of the classification system.
The lateral locations of the discus at release relative to both shoulders were significantly correlated to the measured
distance (r = 0.57 and 0.55, P < 0.001), but not to the classification. Because the lateral locations at release are largely
dependent upon the shoulder abduction angle, the arm positions at the instant of release deserve some attention.
Segment kinematic characteristics at release. The inclination of the upper arm at release was significantly correlated
to both the classification (r = 0.67, P < 0.001) and measured distance (r = 0.51, P < 0.01). This finding shows that the
higher the class, the higher the upper arm position was at release. It is not certain whether this relationship is a result
of the differences in functional capability of the arms or differences in technique, or a combination of both. Gregor et al.
(4) reported that there was a moderate trend for the trunk angle (determined from a side view) became more reclined
as the angle of release increased. Such a phenomenon was also observed in this study. The correlation coefficient
between the trunk angle in the x-y plane and the angle of release was 0.31.
The angular speed of the shoulder girdle at release was significantly correlated to the measured distance (r = 0.47, P
< 0.01), but not to the classification. The angular speed of the upper arm at release yielded significant positive
correlations with the classification (r = 0.57, P < 0.001) and measured distance (r = 0.55, P < 0.001). Because the
speed of the discus at release is determined by the angular speeds of different upper body segments, these findings
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suggested that the angular speeds of the shoulder girdle and upper arm at the instant of release are the discriminating
factors in differentiating the functional differences among wheelchair athletes and effecting the variation in the
measured distance.
Segment kinematic characteristics during the forward swing. Of the segmental ROM examined in this study, all but
the trunk ROM were significantly related to both the classification and the measured distance. The correlation coefficient
values suggested that the shoulder girdle ROM (r = 0.75 and 0.72, P < 0.001) was of greater importance than the ROM
of the upper arm (r = 0.67 and 0.63, P < 0.001) and forearm (r = 0.55, P < 0.001 and r = 0.53, P < 0.01) in
determining the throw distance and medical classification of an athlete. The positive correlations indicate that the
greater the shoulder girdle ROM, the higher or greater is the medical class and measured distance.
Of the segmental average angular speeds identified in the mechanical model showed in Figure 2, only the average
angular speed of the shoulder girdle yielded significant correlations with the classification and measured distance. The
high correlation coefficients (r = 0.75 and 0.79, P < 0.001), together with the ROM results, clearly demonstrated that
the shoulder girdle movement during the forward swing is an important determinant of classification and the variation in
measured distance. These results imply that, within their anatomical and functional limitations, wheelchair athletes
should strive to maximize the potential in trunk movements.
Medical classification of wheelchair athletes is a controversial issue (11). In practice, no disability is totally identical in
any two wheelchair athletes. People with the same level of spinal cord injury may have various degrees of upper body
function. In regard to discus throws, the findings of this study suggest that within the same class, athletes who have
good trunk mobility and control will have an advantage over those who do not have functional trunk movements. This
also suggests that the shoulder function may need to be emphasized in the medical classification of wheelchair field
athletes if such advantage also occurs in the other field events.
RECOMMENDATIONS FOR FUTURE STUDIES
The present study represents the first attempt to describe the movement characteristics of discus throws performed
by wheelchair athletes. More quantitative data, especially those collected during major competitions, are needed for the
development of a data base on performance characteristics. In addition to comparing the performance by athletes of
different classes, future efforts should explore the factors that have the greatest effect on throw distance. It is
anticipated that the accumulated data will provide some scientific information for the ongoing discussion of classification
issues. Specifically, the accumulated data will help to establish objective and reliable functional evaluation techniques
for the medical classification of wheelchair field athletes, which is a very challenging task.
ADDED MATERIAL
JOHN W. CHOW and LAURA A. MINDOCK
Department of Kinesiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
The authors would like to thank Randy Frommater, Todd Hatfield, Tim Millikan, and Marty Morse for their assistance in
data collection and to Les Carlton for his critical review of this manuscript.
This study was supported in part by the Wheelchair Sports, USA and the National Association for Sport and Physical
Education.
Address for correspondence: John W. Chow, 241D Freer Hall, Department of Kinesiology, 906 South Goodwin Avenue,
University of Illinois at Urbana-Champaign, Urbana, IL 61801. E-mail: J-chow1@uiuc.edu
TABLE 1. Subject information.
Throws
Subject ID Classification Mass (kg) Age (yr) Skill Level(FNa) Personal Best (m) 1
1(FNb) F2 100.0 31 Elite 15.50 12.99
2 F2 72.7 25 Elite -- 9.97
3(FNb) F3 95.5 33 Elite -- 17.46
4 F4 77.3 47 Emerging 18.70 17.68
5 F4 77.5 37 Elite 21.88 20.50
6 F4 100.0 22 Emerging 15.22 14.16
7 F5 107.7 48 Elite 27.68 24.00
8(FNb) F5 111.4 26 Emerging 28.00 24.61
9 F5 134.1 51 Elite -- 18.70
10 F5 97.7 46 Elite -- 24.82
11 F5 127.3 20 Emerging 23.50 20.71
12 F6 94.5 27 Elite 22.54 21.01
13 F6 54.5 19 Emerging 18.47 16.60
14(FNb) F7 105.9 48 Elite 40.00 34.25
15 F7 88.6 30 Emerging 26. 00 22.35 21.49 16
FOOTNOTES
a Skill level rated by the Wheelchair Sports, USA.
b 1996 Paralympic medalist in discus throw.
TABLE 2. Means (+/- SD) for selected characteristics of the discus at the instant of release.
Classification
F2 F3 F4 F5 F6 F7
No. of trials 3 2 6 10 4 6
Speed of release (m?s[sup-1])
Horizontal 8.6 (0.6) 11.3 (1.5) 11.8 (1.1) 12.5 (1.1) 12.2 (0.6) 13.8 (
Vertical 6.9 (0.9) 7.2 (0.3) 7.0 (0.5) 7.8 (0.9) 7.7 (0.6) 8.5 (
Resultant 11.0 (1.0) 13.4 (1.4) 13.7 (1.0) 14.7 (1.2) 14.4 (0.8) 16.2 (
Angle of release (°) 38.7 (2.5) 32.4 (2.5) 30.9 (2.4) 31.9 (3.0) 32.1 (0.9) 31.5 (5.
TABLE 3. Means (+/-SD) for the discus location at the instant of release.
Classification
F2 F3 F4 F5
No. of trials 3 2 6 10
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Height above ground (m) 1.42 (0.10) 1.38 (0.06) 1.32 (0.09) 1.34 (0.12) 1.
Forward location relative to seat front (m) 0.13 (0.08) 0.62 (0.14) 0.36 (0.16) 0.42 (0.19) 0.
Location relative to right shoulder (m)
Forward 0.56 (0.05) 0.58 (0.11) 0.58 (0.20) 0.58 (0.13) 0.
Vertical 0.42 (0.13) 0.15 (0.05) 0.27 (0.04) 0.28 (0.10) 0.
Lateral 0.34 (0.04) 0.31 (0.05) 0.54 (0.17) 0.48 (0.16) 0.
Location relative to left shoulder (m)
Forward 0.49 (0.01) 0.74 (0.10) 0.41 (0.33) 0.49 (0.26) 0.
Vertical 0.46 (0.19) 0.25 (0.06) 0.31 (0.05) 0.35 (0.16) 0.
Lateral 0.83 (0.09) 0.71 (0.05) 0.92 (0.09) 0.91 (0.13) 0.
Classification
F7 F8
No. of trials 6 2
Height above ground (m) 1.53 (0.11) 1.53 (0.03)
Forward location relative to seat front (m) 0.35 (0.43) 0.52 (0.03)
Location relative to right shoulder (m)
Forward 0.50 (0.30) 0.57 (0.03)
Vertical 0.30 (0.06) 0.34 (0.02)
Lateral 0.64 (0.18) 0.55 (0.10)
Location relative to left shoulder (m)
Forward 0.52 (0.44) 0.59 (0.01)
Vertical 0.39 (0.09) 0.40 (0.02)
Lateral 1.06 (0.24) 0.93 (0.13)
A positive value indicates that the discus was located in front of, above, or to the right of the reference location.
TABLE 4. Means (+/-SD) for the body segment kinematics at the instant of release.
Classification
F2 F3 F4 F5
No. of trials 3 2 6 10
Segment inclination* (°)
Trunk 63.7 (9.7) 80.8 (1.1) 74.9 (11.2) 73.8 (10.1)
Shoulder girdle 5.1 (8.4) 12.8 (1.3) 5.0 (2.3) 8.7 (7.9)
Upper arm -18.7 (8.0) -17.6 (5.9) -17.4 (2.0) -7.2 (8.8)
Forearm 33.5 (5.9) 0.7 (4.6) 16.5 (6.4) 15.0 (8.7)
Angular speed* (°?s[sup-1])
Trunk 50.4 (5.5) 55.7 (0.9) 64.3 (33.1) 91.9 (42.1)
Shoulder girdle 138.9 (18.3) 205.1 (8.8) 220.5 (66.6) 215.9 (73.6)
Upper arm 595.1 (204.1) 880.8 (60.7) 705.8 (53.1) 890.8 (50.5)
Forearm 1063.2 (361.2) 1340.9 (79.8) 1230.1 (235.6) 1287.8 (160.7)
Classification
F6 F7 F8
No. of trials 4 6 2
Segment inclination* (°)
Trunk 70.5 (4.7) 73.7 (8.6) 80.8 (1.5)
Shoulder girdle 10.2 (2.5) 12.0 (5.4) 9.4 (0.5)
Upper arm -4.0 (6.8) -2.7 (6.3) -0.5 (3.9)
Forearm 16.0 (6.7) 13.1 (8.8) 18.4 (3.3)
Angular speed* (°?s[sup-1])
Trunk 65.7 (69.0) 96.4 (75.7) 21.1 (19.4)
Shoulder girdle 115.4 (37.3) 346.7 (125.1) 160.9 (95.5)
Upper arm 996.2 (123.5) 861.9 (132.7) 968.5 (132.3)
Forearm 1252.8 (151.1) 1207.8 (236.0) 1656.2 (392.6)
A positive value indicates that the distal endpoint was located above the proximal endpoint of the segment.
TABLE 5. Means (+/-SD) for the body segment range of motion and average angular speed during the forward swing.
Classification
F2 F3 F4 F5
No. of trials 3 2 6 10
Segment range of motion (°)
Trunk 23.4 (5.3) 36.0 (0.8) 26.3 (6.4) 32.1 (10.8)
Shoulder girdle 46.8 (12.7) 146.8 (10.8) 57.8 (10.2) 158.1 (25.4)
Upper arm 117.6 (11.5) 188.4 (3.9) 143.8 (7.5) 211.9 (24.9)
Forearm 171.5 (34.6) 209.9 (2.4) 192.1 (16.1) 248.9 (24.7)
Average angular speed (°?s[sup-1])
Trunk 87.2 (6.3) 83.9 (11.9) 100.5 (34.6) 72.4 (23.7)
Shoulder girdle 172.9 (4.8) 341.3 (30.8) 218.9 (56.4) 358.3 (53.8)
Upper arm 451.2 (102.6) 439.8 (62.7) 537.3 (45.6) 481.2 (55.7)
Forearm 641.6 (59.1) 490.5 (74.5) 715.1 (31.4) 566.3 (67.6)
Classification
F6 F7 F8
No. of trials 4 6 2
Segment range of motion (°)
Trunk 20.0 (4.5) 43.1 (12.5) 29.4 (0.1)
Shoulder girdle 125.4 (20.6) 185.9 (32.7) 220.4 (15.5)
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Upper arm 187.0 (12.6) 201.9 (25.6) 242.3 (8.3)
Forearm 215.8 (7.6) 220.5 (15.3) 287.7 (18.6)
Average angular speed (°?s[sup-1])
Trunk 60.5 (21.2) 101.8 (25.2) 58.9 (5.4)
Shoulder girdle 369.8 (90.7) 443.3 (83.5) 441.2 (10.8)
Upper arm 551.8 (108.7) 482.9 (84.9) 486.1 (29.1)
Forearm 634.1 (103.8) 531.5 (100.7) 576.1 (17.1)
TABLE 6. Pearson product moment coefficients of correlation.
Measured
Variable Classification Distance
Discus at release
Horizontal velocity 0.73(FN+) 0.71(FN+)
Vertical velocity 0.55(FN+) 0.83(FN+)
Resultant velocity 0.77(FN+) 0.84(FN+)
Angle of release -0.26 0.03
Height of release 0.39 0.31
Forward location relative to seat front 0.16 -0.08
Location relative to right shoulder
Forward -0.05 -0.44
Vertical -0.01 -0.09
Lateral 0.43 0.57(FN+)
Location relative to left shoulder
Forward 0.06 -0.31
Vertical 0.09 0.01
Lateral 0.40 0.55(FN+)
Body segment at release
Inclination
Trunk 0.17 0.14
Shoulder girdle 0.28 0.20
Upper arm 0.67(FN+) 0.51(FN*)
Forearm -0.24 -0.18
Angular speed
Trunk 0.10 0.05
Shoulder girdle 0.29 0.47(FN*)
Upper arm 0.57(FN+) 0.55(FN+)
Forearm 0.27 0.41
Range of motion during the forward
swing
Trunk 0.29 0.34
Shoulder girdle 0.75(FN+) 0.72(FN+)
Upper arm 0.67(FN+) 0.63(FN+)
Forearm 0.55(FN+) 0.53(FN*)
Average angular velocity during the
forward swing
Trunk -0.11 0.10
Shoulder girdle 0.75(FN+) 0.79(FN+)
Upper arm 0.10 0.22
Forearm -0.29 -0.14
FOOTNOTES
* Significant at the 0.01 level.
+ Significant at the 0.001 level.
Figure 1--Wheelchair field athletes usually adopt either A) a semiforward sitting position which one leg is in front and
the other to the side of the seat or B) a sideward sitting position. Almost every competitor uses some kind of strap to tie
his hips, and one or both legs to the chair to stabilize the lower body. Athletes are allowed to hold on to the chair or a
pole for additional support during the throws.
Figure 2--Factors that determine the measured distance of a throw. The repeated block applies to the dotted lines below
different upper body segments.
Figure 3--Comparison of the measured distances of throws analyzed in this study and the official distances of winning
throws by 1996 Paralympic medalists.
REFERENCES
1. ABDEL-AZIZ, Y. I. and H. M. KARARA. Direct linear transformation from comparator coordinates into object space
coordinates in close-range photogrammetry. In: Proceedings of the ASP Symposium on Close Range Photogrammetry.
Falls Church, VA: American Society of Photogrammetry, 1971, pp. 1-18.
2. ATLANTA PARALYMPIC ORGANIZATIONAL COMMITTEE. Guide to Functional Classifications. Atlanta, GA: Atlanta
Paralympic Organizational Committee, 1996, pp. 25-30.
3. COOPER, L., D. DALZELL, and E. SILVERMAN. Flight of the Discus. West Lafayette, IN: Division of Engineering
Science, Purdue University, 1959, p. 6.
4. GREGOR R. J., W. C. WHITING, and R. W. MCCOY. Kinematic analysis of Olympic discus throwers. Int. J. Sport
Biomech. 1:131-138, 1985.
5. HAY, J. G. and B. YU. Critical characteristics of technique in throwing the discus. J. Sports Sci. 13:125-140, 1995.
6. KRAEMER, H. C. and S. THIEMANN. How Many Subjects?: Statistical Power Analysis in Research, Newbury Park,
CA: Sage Publications, 1987, pp. 55-56.
7. MCCOY, R. W., W. C. WHITING, R. G. RICH, and R. J. GREGOR. Kinematic analysis of discus throwers. Track
Technique 91:2902-2905, 1985.
8. NATIONAL WHEELCHAIR ATHLETICS ASSOCIATION. Official NWAA Rules. Colorado Springs, CO: National
Wheelchair Athletics Association, 1992, p. 2-39.
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9. SCHLÜTER, W. and E. NIXDORF. Kinematische beschreibung und analyse der diskuswurftechnik. Leistungssport
14:17-22, 1984.
10. TERAUDS, J. Computerized biomechanics cinematography analysis of discus throwing at the 1976 Montreal
Olympiad. Track Field Q. Rev. 78:25-28, 1978.
11. WEISS, M. and K. A. CURTIS. Controversies in medical classification of wheelchair athletes. In: Sport and
Disabled Athletes. C. Sherrill (Ed.). Champaign, IL: Human Kinetics, 1986, pp. 93-99.
12. WOOD, G. A. Data smoothing and differentiation procedures in biomechanics. Exerc. Sport Sci. Rev. 10:308-362,
1982.
APPENDIX. MEDICAL CLASSIFICATIONS FOR WHEELCHAIR FIELD ATHLETES
Class Injury Level Functional Capability
F1 C6 Have little control of the discus because finger movements are absent.
F2 C7 Unable to form a fist. Have difficulty in grasping the discus.
F3 C8 Can spread fingers a little and make a fist. Can grasp the discus.
F4 T1-T7 Have no sitting balance. Usually hold on to chair while throwing.
F5 T8-L1 Have movement in backward and forward plane and some trunk rotation.
Have fair to good sitting balance and no functional hip flexors.
F6 L2-L5 Have good balance and movements backward and forward. Have good
trunk rotation. Hip flexion and hip adduction are present. May have
some knee extension and knee flexion.
F7 S1-S2 Have good balance and movements backward and forward. Usually have
very good side-to-side movements.
F8 Minimum disability, almost fully functional.
Class Injury Level Anatomical Capability
F1 C6 Have functional elbow flexors and wrist dorsiflexors. May have
shoulder weakness.
F2 C7 Have functional elbow flexors and extensors, wrist dorsiflexors and
palmar flexors. Good shoulder function. Doesn't have functional
finger flexion.
F3 C8 Have full power elbow and wrist joints. Have full power of finger
flexion and extension, but not functional.
F4 T1-T7 No functional trunk movement, otherwise same as F3.
F5 T8-L1 Normal upper limb function. Have abdominal muscles and spinal
extensors. May have nonfunctional hip flexors. Have no adductor
function.
F6 L2-L5 Normal upper limb function. Have abdominal muscles and spinal
extensors. May have nonfunctional hip flexors. Have a little
adductor function. Similar to F5 but stronger.
F7 S1-S2 Usually can bend one hip backward and one ankle downward. One
side of body is usually stronger. Above knee amputations.
F8 Amputee: either bilateral above knee or single high above knee.
Polio: with one good leg, or bilateral good buttock function. Lower
paraplegia--L5/S1.
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