Introduction: Three models of arm co-ordination were described in front crawl : catch up, opposition and superposition (Chollet et al., 2000). Using the index of co-ordination (IdC), Chollet et al., (2000) quantified the switching from catch up to opposition in relation with enhancement of velocity, expertise, stroke rate, and decrease of stroke length. Lerda et al., (in press) confirmed for lower performers that with expertise and switching from 800m race to 100m race swimmers switched from catch up to opposition or superposition of arms. Using six swim velocities, from 80% to 100% of maximal velocity, Millet et al., (2002) showed that elite triathletes as elite swimmers had similar increase in IdC except that triathletes decrease smoothly IdC at the maximal velocity while swimmers continued to increase it. The triathletes and the swimmers switched from catch to superposition coordination from 95-97% to the maximal velocity. Material and Methods: Thirty-one French men swimmers constituted 2 groups : G1 was composed of the 17 swimmers (22,9±3,8years, 186±3,6cm, 78,8±6kg) with a national 1 and international level (time on a 100m race: 91,3±2,84% of the world record); G2 was composed of the 14 swimmers (21,5±5,3years, 180,5±0,7cm, 71,8±8cm) with a national 2 level (time on a 100m race: 88,4±5,6% of the world record). Eight individual swim velocity were imposed: V3000, V1500, V800, V400, V200, V100, V50, Vmax. The swim velocity was calculated on 12,5m; the stroke rate (SR), the stroke length (SL), the four stroke phases (entry + catch, pull, push, recovery, expressed in % of a total stroke) and the index of co-ordination (IdC) (Chollet et al., 2000) were calculated on 3 strokes filmed by two underwater lateral and frontal video camera (S-VHS, 50Hz). Difference between the two groups and between the eight swimming velocity for each variable are studied by ANOVA and completed by a post-hoc Fisher test. The level of significance was fixed at 0,05 and 0,01. Results: The elite swimmers had a greater velocity and SL (p<0,05) than the non elite swimmers, and a similar SR. Concerning G1, SR increased for each gait (p<0,05) except between V50 and Vmax; SL decreased for each gait (p<0,05) except between V200 and Vmax. Concerning G2, the enhancement of SR and the decrease in SL occurred in two step (p<0,05): from V3000 to V400 and from V200 to Vmax. On the average of the gaits, the elite swimmers (-5,53±6,79%) were significantly (p<0,01) less in catch up co-ordination than non elite (-9,38±4,18%). Concerning the elite swimmers, IdC differences between the swim velocity were significant (p<0,01) and tend to show three patterns : a great catch up co-ordination from V3000 to V400 (from -11,1±4,93% to -7,64±4,78%), a small catch up co-ordination at V200-V100 (from -6,37±4,68% to -2,02±4,78%) and an opposition of arms at V50-Vmax (from 1,03±5,33% to 1,41±5,18%). Contrarily, the non elite swimmers adapted progressively their co-ordination because IdC increased linearly (p<0,01) from V3000 to V50 and decreased non significantly at Vmax; so that they stayed in catch up co-ordination. On the average of the gaits, the elite and non elite men changed their stroke phases (p<0,05) except the recovery which was longer for the non elite swimmers (p<0,01). The elite men increased the pull phase (p<0,01), the push phase (p<0,01), the propulsive phase (p<0,01) further than the non elite swimmers; they decreased the entry + catch phase (p<0,05) and the non propulsive phase (p<0,01) further than the non elite swimmers. These differences between the two groups (p<0,05) concerned V200 to Vmax. Discussion: Concerning the elite men, the co-ordination switch in relation with the swim velocity tend to a transition of three attractor patterns (Haken et al., 1985). The first pattern in a great catch up coordination corresponded to a long-distance race (V3000 to V400), the second pattern in a small catch up co-ordination concerned the long-sprint race (V200-V100). The third pattern in oppositionsuperposition of arms occurred in short-sprint (V50-Vmax) (Chollet et al., 2000; Millet et al., 2002). This adaptation of the co-ordination preferred the decrease in active drag in long-distance race and the increase in propulsive forces from V200 to Vmax (Pelayo et al., 1996). In accordance with Chatard et al., (1990), it arose from a sudden increase in propulsive phase (pull + push phases), a maintain in SL from V200, and a decrease in the entry + catch phase at V50-Vmax. Concerning the non elite swimmers, the co-ordination adaptation was progressive, i.e. they could not have an opposition coordination in sprint because they were not able to increase the pull, the push phases and to decrease the entry + catch phase than the elite swimmers. Indeed, the non elite swimmers kept a catch up coordination, which increased between V50 and Vmax (Millet et al., (20002) concerning the triathletes) whereas a superposition co-ordination could explain a better swimming efficiency (Chatard et al., 1990). A decrease in SL and an increase in SR from V200 did not enable to compensate for a smaller continuity of the arm actions; according with Pelayo et al., (1996) which showed a SR/SL in relation with the swim velocity. To sum up, the lack of expertise could correspond to the incapacity to increase the continuity of the arm actions, jointed to a miss-management of SR/SL when the swim velocity increase.
© Copyright 2002 Expertise in Elite sport. 2nd International Days of Sport Sciences, 12.-15. November 2002, INSEP, Paris (France). Veröffentlicht von INSEP. Alle Rechte vorbehalten.