V significantly decreased through the five zones of each length for the four groups (P < 0.05), corresponding to a decrease from Z1 to Z5 of 50.3% at L1, 37.3% at L2, 42.4% at L3, and 36.8% at L4. This significant decrease in V mainly occurred at Z1 (P < 0.05) and was attributable to the push on the wall after the turn-out (Fig. 3A). G1 significantly increased V by 8.4% at Z5 of L4 (P < 0.05), which was mostly attributable to the final sprint rather than to the underestimation of the Z5 duration. Indeed, only G1 increased V at Z5 of L4, whereas the overestimation of the V measurement concerned the four groups. SR significantly decreased through the four zones of each length for the four groups (P < 0.05) (Fig. 3B). G1 significantly decreased SL through the four zones of L1 and significantly increased it by 10.1% at Z5 of L4 for the final sprint (P < 0.05) (Fig. 3C). G2 and G3 significantly decreased SL by 8.6 and 10.3%, respectively, from Z2 to Z5 in all lengths (P < 0.05) (Fig. 3C). G4 had a constant SL through the four zones of each length (Fig. 3C).
IdC was not significantly different between the elite males and females of, respectively, G1 and G4. It was, however, significantly different between G1, G2, and G3 for the whole 100 m and for each 5-m length (P < 0.05). The high-speed swimmers swam in superposition coordination, whereas G2 and G3 swam in opposition coordination (Fig. 4A). For the whole population, IdC was significantly different between L1 and L2, L2 and L3-L4, and L3 and L4 (P < 0.05). Nevertheless, these changes were significantly different in high- and low-speed male swimmers and between males and females (P < 0.05). The high-speed males (G1) significantly decreased IdC between L1 and L2 and stabilized it from L3 to L4 (P < 0.05) (Fig. 4A). Conversely, G2 and G3 maintained IdC between L1 and L3 and significantly increased it at L4 (P = <0.05), so that they reached superposition coordination at this length. The high-speed females (G4) did not show significant IdC variation during the four 25-m lengths (Fig. 4A). IdC significantly increased from Z2 to Z5 in the four 25-m lengths for the four groups (P < 0.05) (Fig. 4B).
The relative duration of the entry and catch phase (A) was significantly (P < 0.05) shorter for the high-speed groups G1 and G4 than for G2 and G3, whereas the relative duration of the pull phase (B) was significantly longer (P < 0.05) (Fig. 5). The relative duration of the push phase (C) was significantly longer for G1, G3, and G4 than for G2 (P < 0.05) (Fig. 5). Thus, high-speed swimmers were characterized by a significantly longer relative duration of the propulsive phase (B + C) for the whole 100 m and for each 5-m length (P < 0.05). G1 had a relative duration of the propulsive phase similar to that of G4 (respectively, 54 ± 3.8 and 54.4 ± 4.5%), which was significantly higher (P < 0.05) than for G2 and G3 (respectively, 50.9 ± 4.5 and 49.9 ± 4.5%).
During L3 and L4, the high-speed swimmers (G1 and G4) and medium-speed males (G2) had a significantly shorter relative duration of the push phase than did the low-speed male swimmers (G3) (P < 0.05); for G3, the relative duration of the push phase (C) in L3 was 21.4 ± 2.9%, whereas for G1 it was 20.9 ± 2%; for G2, 20.3 ± 2.2%; and for G4, 20.8 ± 1.5%. In L4, the relative duration of the push phase (C) for G3 was 22.9 ± 3.5%, whereas for G1 it was 21.5 ± 1.8%; for, G2 21.4 ± 2.2%; and for G4, 21.6 ± 1.9%. The post hoc Tukey tests (group × length) indicated that the relative duration of the push phase (C) of G3 increased significantly in L4 (P < 0.05), which explained the significant differences in relative duration of the push phase among lengths for the whole population (Table 2).
Lastly, the post hoc Tukey test (group × length) also indicated that for G1, the relative duration of the propulsive phase (B + C) was significantly longer in L1 (P < 0.05), shorter in L2 (P < 0.05), and then relatively stable in the other lengths. For G4, the relative duration of the propulsive phase did not change significantly during the race. For G2 and G3, the relative duration of the propulsive phase significantly increased from L2 to L4 (P < 0.05), explaining the increase in IdC.
All swimmers used a six-beat kick in each length and each zone, revealing stable leg kick.
The main findings of the present study indicate that during a 100-m front crawl, 1) high performance level was characterized by high and stable values of SL and IdC, and 2) the genders were differentiated by the greater SL of males compared with females.
V, SR, SL
The performance-level differences were mainly the greater SR and SL of the high-speed males compared with the others and the capacity to keep these values high throughout the race. This confirmed the findings of previous studies comparing elite with nonexpert swimmers (1,5,8). Recent studies concerning elite swimmers (22,28) have confirmed that the high-speed swimmers (G1 and G4) had stable SL throughout the race and stable V in the last two lengths. On the contrary, the low-speed swimmers (G2 and G3) decreased V and SL throughout the 100 m, which could have been attributable to their incapacity to develop great power output and overcome high drag throughout the race (28). In high-level swimmers with disabilities, Daly et al. (8) have observed an increase in SL at the beginning of the 100 m and have indicated that the race was generally won or lost in lengths 2 and 4, suggesting that these lengths were determinant for the final results. They also indicate that SL explained most of the V changes during the second part of the 100 m. In the present study, the high-speed males and females used a similar strategy. They tended to improve SL in L2 and L4, whereas the low-speed swimmers decreased SL in L3 and L4.
Except at L1, the intralength comparisons confirm that the SL changes explain the V changes quite well throughout the race. At L1, V decreased from Z1 to Z5 by 50.3% because of the diving start (26). During the other lengths, fatigue would explain why V decreased from Z1 to Z5. Alberty et al. (1) have shown that for medium-level swimmers (best time on a 200 m at 78% of the world record), the decrease in V was attributable to decreases in SR and SL. Other studies have confirmed that when swimmers are exhausted, the decrease in V is related to a decrease in SL (7,8,12,30) and a decrease in SR, which is attributable to a 24% decrease in mechanical power output and, hence, slower hand velocity (28). Wakayoshi et al. (30) indicate that improving a swimmer's performance level would be reflected by a decrease in SR, an increase in SL, and a lower energy cost of swimming. In the present study, SL was the best discriminative factor of V. Indeed, the medium- and low-speed groups decreased SL and V throughout the zones of each length, whereas SL remained constant for the high-speed swimmers (although SR decreased whatever the group between the zones of a length). The decrease in SL of the low-speed swimmers may also have been attributable to their poor technique during the turn-out, the effective push on the wall, and the correct timing to restart the stroke movement. Lastly, because the lower-speed swimmers took more time to complete the 100 m than did the high-speed male swimmers, they must swim a longer time in fatigued condition. Therefore, between Z4 and Z5 of L4, V and SL of G2 and G3 continued decreasing while the swimmers were performing the final sprint. Conversely, V and the SL of G1 slightly increased during the final sprint.
Males swam significantly faster than did females, although these high-speed females swam at the same velocity as the low-speed males. This gender effect was related to the male's greater SL, which, in turn, was related to the capacity of males to apply greater power output (25,29) and to overcome greater drag (29). Toussaint et al. (29) report that the greater height and body cross-sectional area of males explain the greater drag that they overcame, developing a greater SL than females. The relationships between anthropometric properties and drag,and thus SL, led to the identification of those anthropometric parameters associated with the greater SL. Grimston and Hay (10) have shown that axilla, hand and foot cross-sectional areas, leg frontal area, and leg and arm lengths were 89% correlated with SL, 41% with SR, and 17% with V. In our study, SL was 38.5% correlated with height, 36.6% with arm span, 50.7% with foot length, and 37.8% with hand length, suggesting that the greater SL of males was associated with their greater anthropometric values.
IdC and Stroke Phases
High-speed swimmers were characterized by a long relative duration of the propulsive phase and, hence, high IdC values throughout the race. First, swimming fast is related to the motor control of swimmers who must solve the propulsion problem of maintaining a great mechanical power output (28), notably by adopting superposition coordination. Chollet et al. (4) and Lerda and Cardelli (14) have indicated that expert males have a higher IdC (i.e., superposition coordination) than do lower performers, who tend to use the arm catch-up and opposition coordination modes. Second, however, swimming fast and adopting superposition coordination are not only responses to organismic constraints (i.e., motor control); they are also the results of environmental constraints (i.e., drag, velocity) (24). The superposition coordination (high IdC) was not the determinant of high V, but it emerged from the high, active drag that swimmers must overcome to swim fast (13,27-29). Indeed, Chollet et al. (4) and Seifert et al. (24) have demonstrated that, concomitant with the increase in drag with V 2 (13,27-29), high-speed swimmers switch from catch-up to superposition over increasing paces from long-distance to sprint pace. Thus, in line with the findings on spatial-temporal parameters, which suggest that the maintenance of high V is related to high and stable SR (26) and SL (5,22), the high-speed swimmers (G1 and G4) adopted their preferential coordination (sprint pattern) and maintained a stable high IdC when interlength comparisons were considered. On the other hand, as regards the intralength comparisons, the high-speed males significantly increased their IdC from Z2 to Z5 of L2, L3, and L4 (22), showing their ability to increase the superposition of the arm actions after a glide time (because of the turn-out).
As did G1, G2 and G3 boosted their swim after the turn-out of each length by increasing their IdC. However, with regard to their lower V than G1, the drag to be overcome (i.e., environmental constraints, drag = KV 2 (29)) was lower, so that G2 and G3 started with a smaller IdC (corresponding to opposition coordination). Moreover, because of their poorer technique and motor control (i.e., organismic constraints)-notably, to restart the stroke movement after the turn-out-G2 and G3 lacked the capacity to adopt a high IdC. Then, on the basis of the interpretation of Alberty et al. (1), who assessed the fatigue effect on IdC changes, it was postulated that fatigue onset led to an increase in IdC, indicating a switch to superposition coordination, in L4. Using an exhaustive exercise, Alberty et al. (1) have shown an increase in IdC from −6.55 to −3.27% in fatigue condition, which was related to a decrease in the relative duration of the nonpropulsive phase (catch and recovery phases) from 61.8 to 57.7% and a corresponding increase in the propulsive phase (pull and push phases) from 38.2 to 42.3%. Alberty et al. (1) have shown that the increase in the pull and push phases with fatigue could be attributable to the decrease in hand velocity, which was in accordance with the findings of Toussaint et al. (28). In the present study, the increase in IdC for G2 and G3 in the second part of the 100 m resulted from a longer relative duration of the hand spent in push phase. However, this motor change was ineffective because, unlike in the high-speed swimmers, SL continued to decrease throughout both lengths and zones, suggesting that the longer relative duration of the push phase of G2 and G3 was related to their smaller hand velocity. Satkunskiene et al. (20) note that swimmers with locomotor disabilities did not take advantage of the push phase. The propulsive force was related to an increase in the pull phase and a decrease in the entry + catch. Satkunskiene et al. (20) postulate that a long push was used more for body balance than for propulsion. Moreover, even though the relative duration of the push phase was longer for G2 and G3, a high average force is not as efficient as a high maximal peak force (6,21,27). In these latter studies, the authors show that the hand undergoes a constant change in direction and alternating acceleration and deceleration during the underwater stroke and is unable to apply high, continuous forces. Thus, to have efficient coordination, swimmers must have effective direction, path, velocity, and hand angle (6,21).
Throughout the race, IdC values and variations were similar for the high-speed males and females. Despite similar arm coordination, however, the females could not swim at the same velocity as the high-speed males. In fact, to swim at the same velocity as the low-speed males, the high-speed females used higher SR and IdC (superposition coordination) than the males, who used opposition coordination. Because these females could not achieve greater SL, they adopted a different motor organization. Seifert et al. (23,24) have shown that at different race paces, males have a higher IdC than females. However, at a given velocity, females have a higher IdC than males (23,24). Toussaint and Beek (27) and Toussaint et al. (29) have shown that females developed smaller mechanical power output and overcame lower drag than did males, explaining their shorter SL. Females compensate shorter SL by changing their arm coordination and SR.
Lastly, the only difference between the high-speed males and females was in L1. Consecutive to the diving start, the higher V of G1 could have been attributable to their high mechanical power output and the high drag overcome to maintain high V during the rest of the length. This management led them to adopt a longer relative duration of the propulsive phase with high IdC, whereas G4 maintained a constant IdC throughout the lengths of the race.
The significant correlation between SL and foot length confirms that the leg kick contributes to the entire propulsion by increasing SL (11) and maximal V by 10% (9). The leg kick also contributes indirectly to propulsion by organizing arm-leg coordination (9,19). The six-beat kick was used by all four groups throughout the entire 100 m, indicating that the change in interarm coordination (IdC) of each group was not related to the leg kick but, rather, to race management, fatigue, and/or performance level.
High performance was characterized by the higher V, SR, SL, propulsive phase, and IdC values seen in the high-speed swimmers compared with the medium- and low-speed swimmers, and by the stability of these values throughout the race. Because of fatigue in L4, medium- and low-speed swimmers spent more time with the hand in push phase and changed to superposition coordination. However, these kinematic changes were ineffective as SL continued to decrease throughout the 100 m.
The gender effect was mainly related to the longer SL of the high-speed males because of the higher drag to overcome and to their higher anthropometric values, notably their greater arm span, height, and foot and arm length that influence propulsion. High-speed males and females had similar IdC; however, the high-speed males showed high IdC from the start of the race, which explains their decrease in IdC between L1 and L2.
The six-beat kick was used by all four groups throughout the entire 100 m, indicating that the change in interarm coordination (IdC) of each group was not related to the leg kick.
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Keywords:©2007The American College of Sports Medicine
BIOMECHANICS; MOTOR CONTROL; RACE ANALYSES; SWIMMING