Inter-subject variability in the upper-lower limb breaststroke coordination
The aim of this study was to assess the inter-subject coordination variability at different skill levels, and as such a cluster analysis among the recreational swimmers was proposed to establish coordination profiling. The elbow-knee continuous relative phase (CRP) was used to analyse upper- lower limbs coupling during a breaststroke cycle. 24 recreational and 24 competitive swimmers swam 25m at 80% of their maximal speed. Underwater and aerial side views were mixed and genlocked. The angular position, velocity, and CRP were calculated for the knee and elbow joints by digitising body markers from the side view. The kinematics of three cycles were filtered, averaged and normalised in terms of the percentage of the total cycle duration. The topography of the CRP curve of recreational swimmers resembled a 'W-shape' whereas an 'N-shape' was noted for competitive swimmers. Competitive swimmer's CRP showed alternation of knee propulsion with elbow propulsion and synchronisation of knee and elbow recovery. The recreational CRP shape showed superposition of contradictory actions. Higher inter-individual variability was observed amongst the recreational swimmers (30.5° vs. 23.0°; p<.05), suggesting that superposition of contradictory actions could be partial or complete. Coordination profiling showed that three clusters could classify the recreational swimmers.