BIOMECHANICAL COMPARISON OF MALE AND FEMALE DISTANCE RUNNERS* Richard C. Nelson, Christine M. Brooks, and Nancy L. Pike Biomechanics Laboratory Pennsylvania State University University Park, Pennsylvania I6802

Interest in distance running among American girls and women has developed rapidly in recent years, This is evidenced by the increasing number of women participating in long distance races including the marathon. Many states have added girl’s championships to their cross country and track and field programs as a consequence of the interest being generated in the high schools. Concurrent with these developments has been the revitalization of women’s track and field and cross country teams in American colleges and universities. The increase in women’s running activities has stimulated many sport scientists to investigate the various aspects of female running performance. These research efforts have focused on the physiological, psychological, sociological, and to a lesser extent the biomechanical factors that influence performance. Studies 1 , of body size and proportions of female distance runners have revealed them to be shorter, lighter, and leaner than other female track and field athletes and females from the normal population fo- comparable ages. However, very little information is available about the biomechanical features of female distance runners. A direct outcome of the increased opportunities for women to participate under better coaching and improved training methods has been the marked improvement in their world record performances. The differences between male and female performances have been reduced steadily and this trend is expected to continue in the next few years. The current status of relative female performance in common running events can be seen in FIGURE1. The male world records are represented by a value of 100 and the female records shown as percentages of the male record for the competitive events from 100 meters to the marathon. The female records are approximately 90% of the men’s with the exception of the 5,000 meters and marathon. The latter two events are very new to women’s competition, so the present differences will no doubt be reduced as greater numbers of female runners train for and compete in the events. The vast majority of the research conducted to date on the biomechanics of running has involved male subjects. Research on female runners has been limited primarily to the study of sprinters such as the work of H ~ f f m a n .Con~ sequently, very little information is available on the biomechanics of female distance runners. This paucity of scientific data combined with the likelihood of increased emphasis on distance running among girls and women suggest that research directed toward a better understanding of the biomechanical aspects would be of both theoretical as well as practical significance.

* This work was partially supported by a grant from the U.S. Olympic Development Sub-Committee for Women’s Athletics, Dr. Harmon Brown, Chairman. 793

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The purpose of the present investigation was to obtain anthropometric and biomechanical data on the best American female distance runners. Such information would reflect the “state of the art” and provide a foundation upon which recommendations for future improvements could be made. A secondary but interrelated purpose was to compare these results with those of male runners of comparable ability, and thereby gain additional insight into female distance running performance.

0

a 0

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FIGURE1. Comparison of male and female world records: 1976.

METHOD Subjects Three groups of distance runners were utilized in this investigation. The first consisted of 21 of the best American female runners (Elite Women) including a number of Olympians and national record holders. The second was comprised of a comparable group of 14 American male distance runners (Elite Men) who had participated in the study by Cavanagh and P ~ l l o c k .The ~ third group consisted of 10 male runners from Penn State University (Penn State Men) who had participated in a longitudinal study previously reported by Nelson and Gregor.6 A summary of the physical characteristics of the three groups is presented in TABLE1. Two male groups of runners who were similar in physical characteristics were included to provide for a more complete comparative analysis with the

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t Student’st-test.

* Standarddeviation.

Penn State Men Group comparisons (t values) t U.S.Women vs U.S.Men U.S.Women vs Penn State Men Penn State Men vs U.S.Men

U.S.Women U.S. Men

Group

0.08 (NS)

6.23 (p

0.82 (NS)

4.65 5.72 3.42

6.56 (p < 0.01)

51.57 63.12 63.43

7.13 (p < 0.01)

4.9 6.7 4.5

Wt (kg) Mean SD

< 0.01) 5.63 (p < 0.01)

165.7 178.0 176.0

Ht (cm) Mean SD * 3.4 4.0

6.39 (p < 0.01)

86.2 94.3

LL (cm) Mean SD 0.01 0.01

2.66 (NS)

0.52 0.53

Relative k g Length Mean SD

TABLE1 DESCRIPTIVE CHARACTERI~CSAND COMPARISON OF FEMALEAND MALEDISTANCE RUNNERS

0.37 0.34

0.39 (NS)

13.49 13.54

Ponderal Index Mean SD

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elite women. The anthropometric comparisons were carried out using data from the elite men, which made possible the direct comparison of the top American male and female distance runners. Unfortunately, insufficient biomechanical data were available for the elite men and hence, it was necessary to incorporate results from the Penn State men in the biomechanical comparisons. Although these restrictions created less than ideal conditions for comparing male and female performers, the scarcity of such information on distance runners tended to override the inherent limitations. Test Procedures The data collection phase of the experiment was carried out in two parts. The first dealt with anthropometric measurements and the second with filming the runners at selected velocities. The physical measurements, which were limited to those presumed to be relevant to running technique, consisted of standing height (Ht), body weight (Wt), and leg length (LL), from which relative leg length (LL/Ht) and ponderal index ( H t / m ) were calculated. The measurement procedures used were those recommended by Clauser et aL6 It was anticipated that these data would aid in the interpretation of the biomechanical results. Cinematographic and film analysis procedures were used to obtain the biomechanical data. The methods used to film the female runners were identical to those utilized with the Penn State Men and have been reported in detail by Nelson and G r e g ~ r .Briefly, ~ the procedures involve having the subject run at maximum velocity, and three predetermined paced velocities over a specified distance on a regular track. The velocities chosen covered a range of speeds from the marathon to sprint events. High-speed 16 mm films (150 framedsec) were taken from which the biomechanical components were derived. Film and Data Analysis Procedures

A Vanguard-Bendix film analysis system with paper tape output was utilized to obtain frame count, X and Y coordinate data from the 6lm. These were used as input data for specially written computer programs that generated values for the specified biomechanical components of the running performance. These variables were: stride length (SL), stride rate (SR), time of support (TS), time of nonsupport (TNS), and stride time (ST). In addition, the actual running velocity was determined for each trial. The distance from the toe of one foot to the toe of the other foot at touchdown was used as a measure of SL. The number of steps per unit of time represented SR in steps per second. The elapsed time from takeoff of one foot to takeoff of the other foot indicated ST, which can also be calculated as the reciprocal of SR. The value for ST included TS, during which the foot was in contact with the ground, and TNS, when the runner was in flight. These parameters were determined for each subject at each of the four velocities that were used in the calculation of interpolated values for the specific experimental velocities. These velocities were selected on the basis of the average speeds required for female world record paces in selected distance events. The seven velocities ranged from 15.86 ft/sec to 22.11 ft/sec spaced

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out at approximately 1 ft/sec intervals. Biomechanical parameters at each velocity for each subject were calculated from the basic data derived from the film analysis using a second order polynomial procedure. This resulted in interpolated data for all velocities, which could then be used for direct comparison of male and female runners. In an attempt to compensate for individual differences in maximum speed, a second analysis was carried out in which relative velocities were utilized. These were based on 60%. 70%, 80%, and 90% of each runner’s maximum velocity. The same method was used to calculate the interpolated values for these velocities as was used for the fixed velocities previously described. This

A N THROPOMETRIC

VARIABLE

FIGURE2. Comparison of physical characteristics of male and female distance runners. procedure represented a somewhat unique approach to the study of running by linking the experimental velocities to each persons maximum level of performance.

RESULTS Physical Characteristics

The results presented in TABLE1 and FIGURE2 reveal that the female runners were significantly (p < 0.01), shorter and lighter than both the elite and Penn State male athletes. They were also characterized by significantly shorter legs, but were similar in relative leg length and ponderal index when

Annals New York Academy of Sciences

798

compared with the elite men. Although the two male groups differed in running achievement, they were similar in height and weight, which minimizes to some extent the limitations imposed by the fact that the best American female runners were compared with collegiate-level male runners. It is important to emphasize the absolute mean differences in height (12.3 cm), body weight (11.55 kg), and leg length (8.1 cm), which have a direct bearing on the biomechanical differences presented in the following section.

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The results for the biomechanical parameters are presented in two sections. The first contains the analysis for absolute velocities and the second for relative velocities. The data for SL and SR presented in TABLES 2 and 4 and FIGURE 3 reveal that for absolute velocities the female runners had significantly shorter strides and higher stride rates. This consistent difference for both variables across all velocities can be seen in FIGURE 3 and is reinforced by the nonsignificant group x velocity interaction (F= 0.01) in TABLE 4. The mean SL for the female runners was 6.4 cm (2.5 in.) less than that for the males (96.5%). It is important to note that this percentage is higher than might be expected based on differences in height (92.5 % ) and leg length (9 1.1% ) As a consequence of their shorter strides female runners necessarily maintain higher stride rates. Their mean values were 0.14 steps/sec higher across all velocities (FIGURE 3). These results show clearly that for female runners to

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22.1 1 2 1.06 19.97 18.62 17.50 16.88 15.86 Group means

(ft/SeC)

Velocity

6.29 6.16 6.01 5.79 5.59 5.46 5.24 5.79

0.320 0.317 0.367 0.419 0.428 0.417 0.380

Women SD Mean

(A)

1.18 1.15 1.12 1.08 1.04 1.02 0.98 1.08

6.51 6.38 6.22 6.00 5.79 5.66 5.44 6.00

0.084 0.062 0.056 0.061 0.062 0.060 0.055

Women Mean SD

0.204 0.219 0.218 0.193 0.163 0.151 0.165

ABSOLUTE

VELOCITIES

1.13 1.11 1.08 1.03 1.00 0.98 0.94 1.04

0.048 0.050 0.049 0.045 0.040 0.037 0.037

Men Mean SD

Relative Stride Length (SL/Ht)

AND RATE AT h . E C " )

Men Mean SD

Stride Length

STRIDE LENGTH

TABLE 2

3.28

3.55 3.46 3.36 3.25 3.17 3.12 3.05

0.238 0.214 0.243 0.281 0.289 0.282 0.254

Women Mean SD

0.110 0.108 0.098 0.086 0.081 0.079

3.31 3.22 3.11 3.03 2.98 2.92 3.14

0.107

3.41

Men Mean SD

Stride Rate (steps/Sec)

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maintain the same velocity as their male counterparts they must maintain a higher tempo to offset the lesser absolute distance covered per stride. The results for relative stride length (SL/Ht) are shown in FIGURE 4. In contrast to absolute SL the female runners have a significantly longer RSL than the male runners (104% ). This indicates that even though they have shorter absolute SL they are covering a disproportionately greater distance per stride as compared to the men. The greater RSL and higher SR values for the females offer two compensatory mechanisms for overcoming their disadvantage imposed by their shorter stature. The temporal components-time of support (TS), time of nonsupport (TNS), and time of support/stride time (TS/ST)-also reveal consistent differences between these groups. The patterns shown in FIGURE 5 and the results contained in TABLES 3 and 4 reveal that the female runners demonstrated lesser values for TS, greater TNS, and lower ratios of TS/ST. The greater absolute TNS is somewhat difficult to reconcile since they are covering less rather than more absolute distance per stride. When the TS/ST ratios are compared, the women show significantly lower values indicating they spent a smaller proportion of their stride time in contact with the ground, and conversely a greater proportion in flight. The results derived from these data for absolute velocities can be summarized as follows. Female distance runners of national caliber differ significantly from their male counterparts in the biomechanical parameters investigated in this study. As a consequence of their lesser stature they necessarily take shorter absolute strides and therefore must maintain higher stride rates to maintain the same absolute velocities. Their longer relative stride lengths indicate that attempts to improve performance by emphasizing longer strides

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appears ill advised. Other differences are observed when stride time is partitioned into contact and Aight times. Here the female athletes have a disproportionately lower absolute contact time and a longer absolute fight time. In addition, their ratios of contact to stride time are less than those for the men. These results suggest that the running technique used by the females is not merely a “scaled down” version of the male model. The results presented so far have been based on absolute running velocities which, from a practical standpoint, are the most important. However the biomechanical components under investigation change as velocity increases from a slow jog up to maximum velocity. Since the two groups of runners differ significantly in mean maximum running velocity (24.8 ft/sec vs 28.2 ft/sec; p < 0.01) it would be of interest to compare them at velocities that are relative to maximum for each individual. Biomechanical parameters were calculated for maximum and relative velocities of 60%, 70%, 80% and 90% of maximum velocity for this analysis. These results are presented in TABLES 5, 6, and 7. Cursory examination of the group means for the biomechanical components for both absolute (TABLES 2 & 3) and relative velocities (TABLES5 & 6) indicates that the values for women are quite similar while those for the men change considerably. This is most likely due to the fact the absolute velocity values for the females cover the same approximate portion of the velocity continuum because their maximum velocities are not too much greater than the top absolute experimental speed (22.1 1 ft/sec). In contrast, the male runners have considerably higher maximum velocities (mean 28.2 ft/sec), and consequently their relative speeds span a portion of the velocity continuum containing higher velocities.

0.138 0.144 0.151 0.160 0.168 0.172 0.180

0.018 0.015 0.015 0.015 0.015 0.015 0.015

Women Mean SD

Group means 0.159

22.11 21.06 19.97 18.62 17.50 16.88 15.86

(ftlsec)

Velocity

0.181

0.157 0.164 . 0.172 0.182 0.191 0.196 0.205

0.012 0.013 0.013 0.014 0.014 0.014 0.014

Men Mean SD

Time of Support

(SeC)

TABLE 3

0.145

0.139

0.012 0.013 0.013 0.014 0.014 0.014 0.014

0.157 0.164 0.172 0.182 0.191 0.196 0.205

0.139 0.142 0.145 0.147 0.147 0.147 0.146 0.017 0.014 0.014 0.015 0.015 0.015 0.014

Men Mean SD

Women Mean SD

Time of Nonsupport (set)

TEMPORAL COMPONENTS AT SELJXTJD ABSOLUTE V E L O C ~

52.3

56.4

3.29 3.43 3.55 3.72 3.86 3.96 4.15

53.3 54.2 55.2 56.5 57.7 58.4 59.6

49.7 50.3 51.1 52.2 53.3 54.0 55.2

3.16 3.25 3.50 3.72 3.73 3.67 3.55

Men Mean SD

Women Mean SD

Time of Support/Stride Time Ratio,TS/ST, ( x 100)

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When the absolute values for SL, RSL, and SR were adjusted to percentages of maximum velocity, the results showed a decrease for the females in comparison to the men. A similar analysis for TS, TNS, and TS/ST showed an opposite trend whereby the females showed an increase in these parameters relative to those of the men. It is clear that basing biomechanical comparisons on velocities that are proportional to an individual's maximum speed does not eliminate the differences between male and female distance runners. Female values for the distance and rate components decreased while the temporal parameters increased in comparison with the men. These results are most likely due to the higher absolute velocities of the men at each relative velocity. In any case the concept of categorizing running velocity as a proportion of a persons maximum velocity

TABLE4 SUMMARY

OF ANALYSES OF

VARIANCE

FOR

BIOMECHANICAL PNUMETERS

(ABSOLUTEVELOCITIES)

F Ratios Velocity

1. Stride length 2. Relative stride

40.51 * 398.25 *

17.54 * 6.50 *

0.01 (NS) 285.50 *

22.03 * 37.52 *

19.00 * 106.51 *

0.00 (NS) 0.08 (NS)

length (SL/Ht) 3. Stride rate 4. Timeof

support (TS)

5. Timeof

nonsuppport 6. TS/STt

Group

Group x Velocity Interaction

Biomechanical Parameter

( Male-Female)

0.92 (NS) 11.15 *

7.72 *

0.17

(NS)

67.16 *

0.06

(NS)

* Denotes significant F ratio (p < 0.01). t Ratio, time of support to stride time. offers a somewhat unique approach. Future research dealing with the physiological and biomechanical aspects of running may be enhanced by incorporating this concept of relative velocity. DISCUSSION

This investigation represents one of the few attempts reported to date in which a direct comparison has been made between male and female distance runners on the basis of biomechanical parameters. Body proportion measures of height, weight, and leg length were also incorporated to aid in the interpretation of the results. The method employed to determine interpolated values for specific velocities made it possible to control for velocity and thereby permit a valid comparison of the two groups. This is of primary importance since most biomechanical factors are influenced by running velocity.

0.255 0.274 0.335 0.311 0.266

0.366 0.366 0.405 0.435 0.467

0.128 0.143 0.158 0.174 0.189

0.014 0.018 0.021 0.019 0.016

0.159

0.125 0.139 0.156 0.176 0.198

0.011 0.013 0.015 0.016 0.018

Men Mean SD

Time of Support

Women Mean SD

Group means 0.1 58

90% 80% 70% 60%

Maximum

Velocity (% of Maximum)

1.08

0.066 0.075 0.086 0.092 0.096

TABLE 6

1.17 1.15 1.11 1.04 0.93

Women Mean SD 0.239 0.193 0.199 0.191 0.176

1.11

0.144

0.139 0.145 0.147 0.147 0.143 0.011 0.012 0.016 0.016 0.015

Women Mean SD

0.121 0.130 0.137 0.140 0.141 0.134

0.009 0.007 0.009 0.011 0.013

Men Mean SD

52.0

47.8 49.5 51.7 54.2 57.0

3.94 4.47 5.00 4.69 4.11

Women SD Mean

53.9

50.7 51.5 53.2 55.6 58.5

2.64 3.11 3.58 3.87 4.15

Men Mean SD

( x 100)

(SeC)

0.247 0.176 0.144 0.125 0.126

Ratio, TS/ST, Time of SupportBtride Time

3.48

4.09 3.74 3.44 3.18 2.96

Men Mean SD

Time of Nonsupport

3.34

3.83 3.53 3.29 3.09 2.95

0.045 0.041 0.052 0.050 0.048

1.18 1.17 1.13 1.07 0.98

Women Mean SD

StrideRate (stepdsec)

Men Mean SD

Relative Stride Length (SL/Ht)

TEMPORAL COMPONENTS AT SELECIED RELATIVE vELOClTD?S

6.39

6.81 6.74 6.53 6.18 5.67

Men Mean SD

Women Mean SD

6.35 90 6.27 80 6.03 70 5.62 60 5.06 Group means 5.87

Maximum

Velocity ( % of Maximum)

(fi)

Stride Length

TABLE 5 STRIDE LENGTHAND RATE AT SELECTED RELATIVEVELOCITIES

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Nelson et al.: Biomechanical Comparison

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The results for body proportion measures support previous studies (Eiben and Malina et d 2 )that indicate that female distance runners are lighter in weight and shorter of stature and leg length in comparison with male runners. The female runners in this study were significantly lighter (81.7%), shorter (93.1%) and had shorter legs (91.4%) than the male runners. Furthermore, they were unable to achieve similar maximum speeds (87.1%). As a consequence of these physical limitations, the females necessarily covered less distance per stride (96.5% ) and performed at higher turnover rates (104% ). However, their relative stride lengths (SL/Ht) exceeded those of the men (104% 1 . With the male model as a reference, it appears that the females are “overstriding,” which may be a means of compensating for their shorter stature (Figure 6 ) .

TABLE 7

SUMMARY

OF

ANALYSES OF VARIANCE FOR BIOMECHANICAL PARAMETERS (RELATIVEVELOCITIES)

F Ratios Biomechanical Parameter 1. Stride length 2. Relative stride

length (SL/Ht) 3. Stride rate 4. Timeof

Group Velocity 54.42 * 45.61 * 120.50 *

5. Timeof

63.53 * 3.38 *

6. TS/STt

18.40 *

support (TS) nonsuppport

( Male-Female)

Group x Velocity Interaction

* * 18.73 *

0.20 (NS) 0.35 (NS)

0.02 (NS) 21.1 *

0.60 (NS) 1.55 (NS)

63.47 4.25

6.22 *

1.87

0.14

(NS)

(NS)

* Denotes significant F ratio (p < 0.01).

t Ratio, time of support to stride time.

It is interesting to note that if the females had in fact been similar to the men in relative stride length, their absolute stride length would thereby have been even shorter by approximately 4 % . If this reduced stride length were subtracted from their absolute length it would result in a value of about 92.5% of the mean male stride length. This proportion is surprisingly similar to differences in height (93.1%) and leg length (91.4%) and further emphasizes the importance of body size to performance. Additional support of this point can be seen in the comparison of female and male world records at distances from 100 to 3000 meters (FIGURE 1). Female performances range from 89% to 91.7% of that of the males. The results for the temporal factors revealed that the female runners were significantly different than the male competitors. It might have been expected that their distribution of TS and TNS would merely be a scaled down version of the male pattern with appropriate adjustment for differences in SR. This was not the case, however, as their TS was disproportionately short and the

806

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TNS unaccountably long. The fact that they were in flight 4% longer than the men, but covered 4% less absolute distance during this time indicates clearly a different running pattern. It appears that the female runners takeoff at a higher angle and therefore greater vertical velocity, which would account for the greater flight time. The shorter contact time of the female runner lends further support to the preceding explanation. It would appear that the center of gravity of the women runners is not as far forward at takeoff. It is strongly recommended that future investigations concentrate on this aspect of female distance running.

ElOMEC HANlCAL

PARAMETER

FIGURE6. Summary of male-female comparisons for the biomechanical parameters.

SUMMARY AND CONCLUSION In contrast with comparable male runners, the best American female distance runners are significantly shorter, lighter, have shorter legs, but are similar in relative leg length and ponderal index. In terms of biomechanical factors, the females had shorter strides, longer relative strides, higher stride rates, lesser times of support, and greater times of nonsupport. Furthermore these differences could not be completely accounted for by the differences in body size. It is concluded that female distance runners differ significantly in running technique in comparison with their male counterparts.

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ACKNOWLEDGMENTS T h e authors wish to express their appreciation to Dr. Doris I. Miller, University of Washington, and Dr. Robert J. Gregor, UCLA. for their assistance during the filming phase of this investigation. REFERENCES 1. EIBEN,0. G. 1972. The Physique of Women Athletes. The Hungarian Scientific Council for Physical Education. Budapest. 2. MALINA,R. M., A. B. HARPER,H. H. AVENT& D. E. CAMPBELL.1971. Physique of female track and field athletes. Med. Sci. Sports 3(1): 32-38. 3. HOFFMAN,K. 1972. Stride length and frequency of female sprinters. Track Technique 48: 1522-1524. P. R., M. L. POLLOCK& J. LANDA.1977. A biomechanical comparison 4. CAVANAGH, of elite and good runners. Ann. N.Y.Acad. Sci. This volume. 5. NELSON,R. C. & R. GREGOR.1976. Biomechanics of distance running: A longitudinal study. Res. Q. 47(3): 417-428. 6. CLAUSER,C. E., P. E. TUCKER,J. T. MCCONVILLE, E. CHURCHILL, L. L. LAWEACH & J. A. REARDON.1972. Anthropometry of Air Force Women. National Technical Information Service Report. AMRL-TR-70-5.

Biomechanical comparison of male and female distance runners.

BIOMECHANICAL COMPARISON OF MALE AND FEMALE DISTANCE RUNNERS* Richard C. Nelson, Christine M. Brooks, and Nancy L. Pike Biomechanics Laboratory Pennsy...
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