Adaptability in swimming pattern: how do swimmers modify propulsive action as a function of speed?

International audienceWe aimed to examine how participants of different skill level adapt their stroke when asked to swim at different speeds. 20 subjects divided into (a) low-(n=6), (b) medium-(n=8), and (c) high-(n=7) expertise level swam in front crawl at four different swim paces of 60, 70, 85 and 100% of their maximal speed in a swimming flume. Eight force sensors placed on the dominant hand helped to determine kinetic parameters (force impulse over 5sec I + ; arm stroke impulse I + /arm , which are calculated on integral of the force-time curve). Stroke frequency (SF), stroke length (SL), stroke index (SI), Index of coordination (IdC), propulsive phase duration both in percentage of total cycle (PrP%) and absolute duration (PrPs) were determined using four underwater cameras. Results showed that those populations clearly differ in SL and SI, both indicators of swim efficiency. Whatever the skill, increase in swim speed is highly correlated with I+. However, no clear conclusion could be drawn from the magnitude of kinetic (I+, I + /stroke , F average , P pull , P push) and coordination (IdC, PrP%, PrPs) parameters, which were similar in magnitude in low-and high-level swimmers. But examination of adaptive strategies showed that if all swimmers increased I+ by increasing their stroke frequency, medium-and high-level swimmers were capable of reorganizing inter-arm movement coordination patterns to increase I + /arm. This study shows how more skilled swimmers adapt their coordination in a subtle way to get attuned with their environment. List of acronyms I + : force impulse over 5 seconds I + /arm : force impulse over 1 cycle in the right hand SF: stroke frequency Fpull: force (in N) developed duing pull phase Fpush: force (in N) developed durint the push phase. PrPs: absolute time of propulsive phase duration (in s) PrP%: time of the relative duration of the propulsive phase