The effects of leg kick on swimming speed and arm-stroke efficiency in the front crawl

Purpose: To analyze the effects of swimming pace on the relative contribution of leg kick to swimming speed and to compare arm-stroke efficiency (η_F) assessed when swimming with the arms only (SAO) and while swimming front crawl (FCS) using individual and fixed adjustments to arm-stroke and leg-kick contribution to forward speed. Methods: Twenty-nine master swimmers (21 men, 8 women) performed SAO and FCS at 6 self-selected speeds from very slow to maximal. The average swimming speed (v), stroke frequency (SF), and stroke length (SL) were assessed in the central 10 m of the swimming pool. Then, a 2nd-order polynomial regression was used to obtain values of v at paired SF. The percentage difference in v between FCS and SAO, for each paired SF, was used to calculate the relative contributions of the arm stroke (AC) and leg kick (LC) to FCS. Then η_F was calculated using the indirect “paddle-wheel” approach in 3 different ways: using general, individual, and no adjustments to AC. Results: The LC increased with SF (and speed) from –1% ± 4% to 11% ± 1% (P < .05). At the lower FCS speeds, η_F calculated using general adjustments was lower than η_F calculated using individual adjustments (P < .05), but differences disappear at the fastest speeds. Finally, η_F calculated using individual adjustments to LC in the FCS condition did not differ with η_F assessed in the SAO condition at all the investigated speeds. Conclusions: The relative contributions of the arm stroke and leg kick should be individually estimated to reduce errors when calculating arm-stroke efficiency at different speeds and in different swimmers.