The effects of leg kick on the swimming speed and on arm stroke efficiency in 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 (ηf) 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 males, 8 females) performed SAO and FCS at six self-selected speeds from very slow to maximal speed. The average swimming speed (v), stroke frequency (SF),stroke length (SL) were assessed in the central 10 m of the swimming pool. Then, a second-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 ηf was calculated using the indirect “paddle-wheel” approach in three 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<0.05). At the lower FCS speeds, ηf calculated using general adjustments was lower than ηF calculated using individual adjustments (p<0.05) but differences disappear at the fastest speeds. Last but not least, ηf calculated using individual adjustments to the leg kick contribution in the FCS condition did not differ with ηf 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 different swimmers.