Propulsion and symmetry within the stroke cycle: a comparison between tethered and free swimming

BACKGROUND: Asymmetry of propulsion is a key factor when the movements of two limbs occur in sequence. Considering the difficulties in quantifying thrust forces during free-swimming, tethered-swimming is proposed as an alternative tool. The purpose of this study was to investigate the thrust forces during tethered and free-swimming, including the effect of hand dominance. METHODS: Eleven swimmers were analyzed during 10-s all-out front-crawl swimming test in both conditions using only arms. Two pressure sensors were attached to each swimmer's hand (palmar and dorsal side) to estimate the propulsive forces as the horizontal component of the product of hand differential pressure and hand surface. Propelling forces in terms of average (FMEAN), impulse (I), peak (FPEAK), and as a pattern within the stroke cycle values were analyzed. RESULTS: Larger hand propulsion was found in tethered than in free-swimming (~16%, 11%, and 21%, for FMEAN, FPEAK, and I, respectively). The SPM analysis highlighted larger values only at the beginning of the cycle (from 7% to 42%). Dominance analysis revealed a higher FPEAK (~12 N) in the dominant limb than in the nondominant limb in both swimming conditions. CONCLUSIONS: Larger hand force in tethered than free-swimming conditions is explained by differences from entry to catch phase.