Swimming intensity substantially influences intersegmental coordination in breaststroke; however, its specific impact on spatiotemporal organization of the lower-limb action remains unclear. This study investigated kinematic modifications of the breaststroke kick during maximal versus submaximal intensities using a dual approach of discrete variables and time-series analyses. Nine competitive male swimmers performed 25-m breaststroke trials at both intensities while three-dimensional kinematics were captured using a multi-camera motion analysis system. The kick cycle was divided into “leg sweep”, “leg lift and glide”, and “leg recovery” phases. Data were analyzed using paired t-tests for discrete metrics and Statistical Parametric Mapping (SPM) for time-series trajectories, with normalization applied to both the total kick cycle and individual phase durations. Submaximal swimming was characterized by significantly longer absolute and relative durations of non-propulsive phases, specifically the “leg lift and glide” phase (59.09 ± 5.72% vs. 34.45 ± 12.11% in maximal, p < 0.001), resulting in a 50.3% greater horizontal centre of mass displacement per kick (2.24 ± 0.38 m vs. 1.49 ± 0.30 m in maximal, p < 0.001) despite lower swimming velocity. Conversely, maximal swimming elicited compressed phase timing, earlier occurrence of peak joint events and higher angular velocities, particularly near phase transitions, and greater vertical centre of mass displacement. Notably, joint ranges of motion and segment widths remained consistent across intensities, indicating a preservation of the spatial movement patterns. These findings demonstrate that lower-limb action adaptations to swimming intensity in breaststroke are predominantly driven by temporal reorganization and phase-coordination shifts rather than spatial modification of the joint trajectories.
Gourgoulis et al. (Fri,) studied this question.