Introduction Breaststroke is a simultaneous swimming where arm and leg are alternately propulsive and is subject to slowing down and increases of speed more than any other strokes as it is related to forward movement drags. The breaststroke efficiency is associated to the decrease of propulsive discontinuity and consequently to the synchronisation of motor actions (Sanders, 1996). For the expert swimmer, when switching from 200m to 100m breaststroke, velocity increase is combined with frequency increase. However, unlike the other 3 strokes, it leads to a decrease in stroke length (Chollet et al, 1996). The swimming phases of a cycle are not modified in the same manner as velocity increases (Chollet et al, 1999, Vilas Boas et al, 1994). The aim of this study was to identify the differences between arm-leg synchronisation of non expert versus expert breaststrokers as an increase of swimming velocity. Methods Population - 16 international and national expert swimmers (8 males and 8 females) and sixteen regional non expert swimmers (8 males and 8 females) took part in this study. Their characteristics are shown in the following table: Process - The protocol consisted of swimming 3 times a 25m breaststroke at increasing speed (200m, 100m, and 50m speed). Data collection: During the entire test, underwater window views were shot with video cameras (side and front views). Those 2 cameras were linked to a digital audio-visual mixer showing the views side by side. A video timer integrating a stopwatch (1/100th s.). A third above camera recorded the swimmers so as to measure precisely the velocity. Pictures treatment: For each swimming velocity, a video timer (1/50th of a second) gave the total duration of three representative stroke cycles. The key moments were determined by using the total duration of each cycles and picture pause. The number of video frames separating the markers gives the time run off between each cycle marker. Five phases corresponding to the interval between 2 markers are distinguished: leg propulsion, glide, arm propulsion, arm recovery and leg recovery. The relative percentages are calculated by using the respective duration of each phase. Statistical analysis: The statistical processing used a variance analysis for repeated measures with Systat application program. The expert and non expert differences between each synchronisation phases were calculated with Student t test. Results Velocity, stroke rate and stroke length These parameters were expressed with non-experts' / experts' differences. Velocities are obviously different. Stroke rates are not significantly different, even if it increased with velocity. In each group, the stroke length decreased when the velocity increases. The stroke length is greater for the expert group than for the non expert, for all velocities. Arm and leg synchronisation The non expert / expert differences are shown in a table Discussion The velocity increase determined by the protocol showed a frequency increase and a stroke length decrease in accordance with previously published material (Chollet et al, 1996). The significant reduction of glide time along with velocity increase logically depends on the increase of forward movement drags. The specific differences between non expert and expert swimmers concerned particularly experts' capacity to optimise the propulsive phases, while applying propulsive forces on a longer time period. This study showed that in breaststroke, the expertise is distinguished by greater motor action continuity in relation with a capacity to favour propulsive phases, to decrease glide lag time and to perform the leg recovery more rapidly.
© 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.