JOURNAL OF APPLIED BIOMECHANICS, 1996,12,197-206 8 1996 by Human Kinetics Publishers, Inc.

Stroking Characteristics in Freestyle Swimming and Relationships With Anthropometric Characteristics

Patrick Pelayo, Michel Sidney, Tarik Kherif, Didier Chollet, and Claire Tourny

The purpose of this study was to determine the relationships between velocity, stroke length, and stroke rate in freestyle competitive events in order to compare male and female swimmers' results and assess their relationships with anthropometric charac- teristics. Three hundred three male and 325 female swimmers of national and interna- tional levels were tested during competition. Solutions adopted in each freestyle event had specific characteristics affecting the stroke ratelstroke length ratio according to distance of the race. Differences in velocity between men and women primarily re- sulted from differences in stroke length. If the velocity and stroke ratelstroke length ratio depend on the distance swum and the sex of the swimmer, this survey shows the nondiscriminating aspect of anthropometric characteristics. Although swimmers achieved very similar velocity values with different combinations of stroke length and stroke rate, one must appreciate the average time and space characteristics currently used by the best male and female swimmers to optimize their performances.

The velocity (V) of swimming is governed by stroke length (SL) and stroke rate (SR). Different research teams have studied optimal SLISR ratio according to velocity (Craig & Pendergast, 1979; Craig, Skehan, Pawelczyk, & Boomer, 1985; East, 1970) and the variations introduced by swimming styles (Changalur & Brown, 1992; Kennedy, Brown, Chengalur, &Nelson, 1990; Pai, Hay, & Wilson, 1984), by the distance of the race (Craig & Pendergast, 1979; East, 1970; Keskinen & Komi, 1993; Pelayo, Chollet, Sidney, & Toumy, 1994), or throughout the course of the race (Hay & Guimares, 1983; Letzelter & Freitag, 1982). These authors reported that similar swimming performances are character- ized by greater variability in SL than in SR. Observations made during international com- petitions (e.g., Satori, 1975, 1976) have shown that the combination of SR and SL in producing V is highly individual. Among the factors that may influence the relationship between SR and SL and affect swimming speed are anthropometric parameters that have been shown to be related to stroke rate and, more importantly, stroke length. Specific anthropometric characteristics such as body form and size, surface area of propulsive segments, and floating capacity have been identified by Toussaint et al. (1983), Chatard,

P. Pelayo, M. Sidney, and T. Kherif are with Laboratoire d' Etudes de la Motricit6 Humaine, Facult6 des Sciences du Sport et de I'Education Physique, Universitt? de Lille 1I,9 rue de I'universitk, 59790 Ronchin, France. D. Chollet and C. Tourny are with Centre d'optimisation de la Performance Motrice, UFR STAPS, Universie de Montpellier, France.

198 Pelayo, Sidney, Kherif, et al.

Padilla, Cazorla, and Lacour (1985), and Grimston and Hay (1986) as factors whose influ- ence on performance is very important and which also influence stroke mechanics. In contrast, previous studies (Katch & Michael, 1973; Smith, 1978) reported low correla- tions between anthropometric parameters such as height and final times for both male and female swimmers (correlations were even nonexistent with males in the study by Siders, Lukaski, & Bolonchuck, 1993). Despite the research activity referred to, there appears to be a paucity of information regarding the direct influence of anthropometric characteris- tics on toplevel swimming.

The purpose of this study was to determine the relationships between V, SL, and SR during competition in all the freestyle competitive events (50-m, 100-m, 200-m, 400-m, 80011,500-m), to compare the results obtained by male and female swimmers, and to assess the relationships between these parameters and anthropometric characteristics. We believed this would enable us to specify whether these characteristics were discriminating factors in the performances of top-level swimmers.

I I

Materials and Methods f Two procedures of assessment in real competition conditions were used for this study. In the first assessment procedure, 303 male and 325 female swimmers of national and international levels were tested in real competition conditions (in a 50-m pool) during international meetings at Canet in 1990, 1991, 1992, and 1993; at the French 1992, 1993, and 1994 winter championships; and at the Mediterranean championships in 1993 (male: 50-m, n = 57; 100-m, n = 73; 200-111, n = 56; 400-111, n = 73; 1,500-m, n = 44; female: 50-m, n = 65; 100-m, n = 73; 200-m, n = 64; 400-1-11, n = 73; 800-111, n = 50). In the second assessment procedure, 88 male swimmers (50-m, n = 21; 100-m, n = 20; 200-m, n = 23; 400-111, n = 24) and 85 female swimmers (50-m, n = 20; 100-m, n = 21; 200-111, n = 22; 400-m, n = 22) were tested during the same events but only for the freestyle 50-m, 100-m, 200-m, and 400-111 events. These swimmers, among whom were Olympic medalists, were mostly European.

For the first procedure, all events were recorded with four S-VHS video cameras. Velocity was calculated every 50 m from the printed output of the automatic timing de- vice. SR was measured three times across the length of the pool using a Seiko frequency meter (base 3) and expressed in cycles per minute (cycles - min-I). SL was calculated by dividing the 50-m velocity by the stroke frequency (SRl60). These calculations overesti- mated the real distance swum within each stroke cycle; Craig et al. (1985) showed that correcting the calculated distance per stroke for the turns uniformly decreased these val- ues by approximately 5%. Analysis of East's data (1970) indicated that these inherent errors do not influence comparisons of different groups of swimmers very much. There- fore, for a thorough evaluation of a great number of subjects, we decided not to attempt a correction of the data with these uniform factors in all comparisons.

The second procedure was very similar to that of Kennedy et al. (1990). The mea- sures taken over a distance of 15 m, in order to ignore the changes in speed at start and turns, were used to study the relationships between stroking characteristics and anthropo- metric parameters. Thus, the second stage consisted of measuring the velocity over a dis- tance of 15 m (V,,) as well as the stroke rate from a videotape of the finals according to the following protocol. Two S-VHS video cameras running in sync, set 15 m apart along the central part of the pool and connected to a timer, enabled us to assess the value of V,,. Frequency was measured in the same way as in the first procedure. The distance per cycle over 15 m (V,,) was calculated from the V,JSR ratio. The ages of the swimmers and

Freestyle Swimming 1 99

anthropometric measurements such as height, arm span, weight, and foot size were also recorded during the same competitions. The difference between height and arm span, the heightlweight ratio, and the area of skin surface were calculated according to the Dubois and Dubois (1916) formula.

Statistical Analysis

Means and standard deviations were computed for all the measured variables. One facto- rial analysis of variance (ANOVA) was used to show significant differences in SR, SL, andV values (dependent variables) between men and women (independent variable). Stu- dent t tests were used to establish significant differences between each distance event in male and in female groups. Stepwise regression was used between V,,, SL,,, SR, and all the anthropometric variables. In all comparisons, the significance threshold was set a tp < .05 (*) and p < .01 (**). In the stepwise regression, only the variables that added signifi- cantly to prediction @ < -05) were included in the final regression equation.

Results

Descriptive statistics for the first procedure appear in Table 1. Variations of the average stroke length and average stroke rate according to the speed of the races (50-m, 100-m, 200-m, 400-m, 800 or 1,500-m) for male and female swimmers are shown in Figures 1 and 2. Velocity was significantly different @ < .01) between male and female swimmers for each distance. Stroke length was significantly higher in male than in female swimmers in each distance event (p < .01). In male swimmers, SL was significantly different be- tween the 50-m, 100-m, 200-m, and 400-m events, but SL for the 1,500-m event was different only from that of the 200-m event (see Figure 1). In female swimmers, the differ- ences were significant @ < .01) between each event except when we compared the 50-m

Table 1 Means and Standard Deviations of Velocity, Stroke Rate, and Stroke Length for Male and Female Swimmers in Freestyle

Sex Event

Velocity Stroke rate Stroke length (m - s-I) (cycles - min-I) (m . cycles-')

M SD M SD M SD

Males 50 m (n = 57) 100 m (n = 73) 200 m (n = 56) 400 m (n = 73) 1,500 m (n = 44)

Females 50 m (n = 65) 100 m (n = 73) 200 m (n = 64) 400 m (n = 73) 800 m (n = 50)

**Difference between male and female swimmers statistically significant @ < .01).

Pelayo, Sidney, Kherif, eta/.

Figure 1 - Evolution of mean f SD values of stroke rate (-I)) and stroke length (+) with mean values of velocity corresponding to distance of race (1,500-m to 5Qm) for top-level freestyle male swimmers.

Female

Figure 2 - Evolution of mean f SD values of stroke rate (-I)) and stroke length (+) with mean values of velocity corresponding to distance of race (1,500-m to 50-m) for top-level freestyle female swimmers.

with the 400- and 800-m events, the 100-m with the 200-m event, and the 400-m with the 800-m event (see Figure 2). Stroke rate values were not significantly different between male and female swimmers from the 50-m to the 400-m, but differences appeared when we compared the 800-m to the 1,500-m @ c .01). Stroke rate increased significantly @ c .01) as distance decreased for male swimmers. For females the stroke rate evolved in

Freestyle Swimming 201

the same way as for male swimmers but stopped decreasing from the 200-m up to the 800- m event.

Results dealing with the anthropometric characteristics and stroking characteristics measured in the second procedure are summed up in Table 2. Variations of V,,, SL,,, and SR were similar to those observed in the first assessment. Both V and SL values measured in the first procedure were significantly higher than V,, and SL,, values measured in the second procedure because the latter did not take into account starts and turns. Age and anthropometric characteristics were always significantly different @ < .01) between the two sexes. Female swimmers were younger and had a less sizable gauge (height, span, weight, and foot size) than male swimmers. No significant differences @ > .05) in

Table 2 Velocity (V,,), Stroke Length (SL,,), Stroke Rate (SR), and Anthropomorphic Characteristics According to the Distance Swum in Freestyle

Velocity Stroke rate Stroke length Age (m . S-I) (cycles . min-I) (m . cycles-') (years)

SexIEvent M SD M SD M SD M SD

Males 50 m (n = 21) 100m(n=20) 200 m (n = 23) 400 m (n = 24)

Females 50 m (n = 20) 100m(n=21) 200 m (n = 22) 400 m (n = 22)

Height span Body mass Foot size (cm) (cm) (kg) (French)

SexlEvent M SD M SD M SD M SD

Males 50m(n=21) 100m (n = 20) 200 m (n = 23) 400 m (n = 24)

Females 50 m (n = 20) 100 m (n = 21) 200 m (n = 22) 400 m (n = 22)

Difference between male and female swimmers statistically significant :*p < .05. **p < .01.

I 202 Pela yo, Sidney, Kherif, et a/.

anthropometric characteristics appeared between the different distances for male swim- I mers. In contrast, for females, we can observe significant differences 01 < .05) between the short-distance events (50-m and 100-m), in which the gauges were most important, and the medium-distance events (200-m and 400-m) although ages were similar @ > .05).

The results of the stepwise regression technique are presented in Table 3. Anthropo- metric characteristics did not have the same influence on stroking characteristics (V,,, SL,,, and SR) of males as of females. No significant discrepancy appeared with males on each event distance. On the contrary, anthropometric characteristics were generally better correlated with females (see Table 3). Age, height, and span were correlated with stroking characteristics on 50-m and 100-m events. No significant discrepancy appeared for the 200-m event. For the 400-111 event, only weight was correlated with V,,.

Discussion I The average velocity values of male swimmers measured in this study and expressed as percentages of world records were higher (93.1 %) than those of female swimmers (91.5%). The mean velocities for the 100-m and 200-m events were very high (93.7% for the 100- m and 94.2% for the 200-111); this was partly due to the participation at the Canet meetings of Olympic champions and other medalists of the 100-111 and 200-m events, and it was also due to the fact that selections for the 4 x 100-m and 4 x 200-111 relays of the national teams were conducted during these competitions. Because of the number and high level of swimmers in this investigation, our data provide a good reference base for the characteris- tics of solutions chosen by elite competitive swimmers; the last reference base dates back to the Olympic games of 1988 (Kennedy et al., 1990).

Velocity, which was significantly different between men's and women's perfor- mances @ < .01), also decreased significantly from the 50-m race up to the 800- and 1,500-m races. Velocity decreased less from the 50-m race up to the 400-m race in female swimmers (V100N50 = 92.4%, V200N50 = 85.3%, V400N50 = 82.1%, V800N50 = 80.4%) than in male swimmers (V100150 = 91.9%. V200150 = 83.4%, V400150 = 78.7%, V1,500N50 = 74.4%), as was previously noticed by Pendergast, di Prampero, Craig, Wilson, and Rennie (1977) (see Figure 3). This effect can be explained by the fact that women have a higher percentage of fat, which influences buoyancy in swimming and increases swimming economy (Holmer, 1974; Stager, Cordain, & Becker, 1984). I Table 3 Results of Stepwise Regression Between Velocity (Via, Stroke Length (SLJ, Stroke Rate (SR), and Anthropomorphic Characteristics in Female Swimmers

Event V,, (m . s-I) SL,, (m . cycle-') SR (cycles. min-')

50 m - Age (r = .83) Span (r = .46) Span (r = .69)

100 m Age (r = .49) Height (r = .57) Height (r = .44) Height (r = .72) Span (r = .57) Span (r = .44)

200 m - - - 400 m Weight (r = .44) - -

Note. Dashes indicate no significant results.

Freestyle Swimming

----D-- %WR male

-.-- *-.- %V female

701 . . . , . , . t . , . r . I . I . I . l . I . l . I . , . 1

0 100 200 300 400 500 600 700 BOO 900 1000 1100 1200 1300 1400 1500

Dlslnnee

Figure 3 - Comparison between decrease in velocity corresponding to distance of race (50-m to 800 or 1,500-m) expressed as percentage of maximal speed of the 50-m event for the average v a W of the present study and male and female world records.

Velocity values of the different events were significantly higher @ c .01) in the first procedure since they accounted for starts and turns. The average differences were about 4.5% and 5.3% for male and female swimmers, respectively. Consequently, SL values were higher than SL,, values measured in the second procedure, with average differences of about 4% and 6% for male and female swimmers, respectively. This difference be- tween men and women can be explained by men's advantage in starts and turns owing to their greater muscular power. The calculations of the first assessment globally overesti- mated velocity and stroke length approximately 5%, in agreement with data of Craig et al. (1985). However, the results of the second procedure, analyzed according to East's data (1 970), indicated that these inherent errors do not influence comparisons of different groups of swimmers very much considering the identical statistical results. Globally, the results of this study were largely in accordance with previous data collected by East (1970), Satori (1975, 1976), Craig and Pendergast (1979), Letzelter and Freitag (1983), Hay and Guimares (1983), Pai et al. (1984), Craig et al. (1985), and Kennedy et al. (1990).

There was no significant difference in SR between male and female swimmers. SL was thus the main contributor to the higher velocity of the male swimmers. Since the magnitude of stroke length is related to the propulsive forces that a swimmer exerts while stroking, differences between male and female swimmers in both strength and body size may account for the observed differences in velocity. According to the results obtained by Toussaint et al. (1983) in an investigation of two groups of different levels, the difference in stroke length between male and female swimmers could be related to the smaller body size of women. Moreover, differences between height and span (7.39 f 6.02 and 3.99 f 6.01 cm for male and female swimmers, respectively) may explain the difference in stroke length.

For both male and female swimmers, the most important means of increasing freestyle swimming velocity during short-distance competition (50-m, 100-m, and 200-m) is to increase stroke rate. The shortest distance event (50-m) was performed with significantly higher SR values. The highest values of stroke length were recorded during the 200-m event for both male and female swimmers. SL increased significantly on short distances

Pelayo, Sidney, Kherif, et a/. I (from the 50-m up to the 200-m event) and decreased from the 200-m up to the long distances (80011,500-m). Variations in energy expenditure may account for this phenom- enon. Indeed, it is in the 200-m event that the highest power can be developed per cycle. The strategy for the medium long-distance event (400-m, 800-m, and 1,500-m) is to reduce power expanded per cycle in order to maintain the highest stroke rate values dur- ing the whole course of the race. In contrast, the very high values of stroke rate used on short distances (100-m and 50-m) cannot allow a swimmer to develop high stroke length values.

No significant differences in anthropometric characteristics were seen between male competitors in the different distance groups. Although the same trends were apparent for female swimmers, height, arm span, weight, and foot size measurements were lower for the 200-m and 400-111 events than for the 50-m and 100-m events. These results are in accordance with those recorded by Carter and Ackland (1994) for 231 male and 170 fe- male swimmers during the sixth world swimming championships held in January 1991. In the present study, stepwise regression technique showed that anthropometric characteris- tics did not influence V,,, SL,,, and SR in male swimmers; this finding was contrary to findings of other studies (Grimston & Hay, 1986) but in accordance with those of Smith (1978) and Siders et al. (1993). The present survey of a group of preselected and homoge- neous male swimmers showed the nondiscriminating aspect of anthropometric character- istics in the achievement of performances. These results failed to indicate that body size can be correlated with swimming performance and stroking characteristics for top-level male swimmers. In fact, anthropometric characteristics may have influenced swimming success earlier in these swimmers' careers (Blanksby, Bloomfield, Ponchard, & Ackland, 1986). In contrast, in female swimmers, anthropometric parameters (age, height, and span) were correlated with stroking characteristics in 50-m and 100-m events (see Table 3). However, these data raise the question whether determining SRISL ratio from anthropo- metric parameters is reasonable and useful for coaches (see Table 3). In addition, weight seems to be a drawback for swimming performance in the 400-111 event for female swim- mers (V = 1.62 - 3.32 . - weight).

There are two possible reasons why anthropometric variables are better predictors of V, SR, and SL in female than in male swimmers. First, female performance levels were lower than male levels. Second, the average difference between height and arm span in male swimmers (7.39 + 6.02) was significantly higher @ < .01) than that measured from a standard group of male subjects of the same age (0.36 f 3.51 cm for 202 sedentary males, unpublished data from our laboratory). On the other hand, these values were very similar to those of sedentary females (2.61 f 3.78 cm for 167 sedentary females vs. 3.99 f 6.01 for female swimmers, unpublished data from our laboratory). These two reasons can ac- count for a higher heterogeneity in anthropometric parameters for female swimmers that could influence velocity and stroking characteristics in the same way as for a population of nonelite or young swimmers.

Conclusion

The results show that the SWSL ratio chosen in each freestyle event has specific charac- teristics according to the distance of the race. Velocity and SWSL ratio in freestyle depend also on the sex of the swimmer. Stroke rates observed in females were close to those of males on each distance event (from 50-m to 400-m). The lower velocities of females can be explained by lower stroke length values. This survey of a group of top-level swimmers shows the nondiscriminating aspect of anthropometric characteristics in the performance

Freestyle Swimming 205

achievements of male swimmers, contrary to females. Although swimmers achieved very similarV values with different combinations of SL and SR, one must appreciate the aver- age time and space characteristics currently used by the best male and female swimmers to optimize their performances. This finding furthermore emphasizes the importance of regularly investigating time and space characteristics in competitive conditions in order to determine the transformations associated with changes in strategies or technique.

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