Abstract
Scientific opinions about the importance of dolphin upward leg movements for swimming performance are still divided. Research on the efficiency of propulsion, similarly generated by a relatively larger the monofin surface, showed that quality of the upward movement phase is a measure of swimming performance. Therefore, the forces generated as a result of upward and downward kicks in butterfly swimming were analysed. The ability of the swimmers to kinaesthetically control of the upward dolphin kicking was also researched. Ten international level butterfly swimmers (mean 18,2±1,4 years) took part in the research. They performed three trials on 25m distance, at maximum speed using the monofin device (The plate of standard monofin was removed and two strain gauges were affixed in the middle, between the toe). They randomly swam: 1) butterfly stroke (BS), 2) dolphin-kicking only (LK) and 3) swam being focused on activation of upward-kicking (AUK). Time dependent signals of the force sagging the fin in reaction to the water resistance were registered. The impulses of force sagging the fin in each stroke were lower in upbeat than in downbeat. The lowest difference was in AUK trial. First, Wilks's test and then Duncan’s post hoc tests for each of the trial showed (at p≤0,05) that: downward impulses for LK was significantly higher than for BS. Upward impulses did not differ between the trials. Downward times for AUK, the same as total trial times, was significantly longer than for BS and for LK Upward times for AUK was significantly longer than for BS. The results demonstrated, that butterfly arms action leads to intensification of both kicking phases. The swimmers were well skilled for kinaesthetic controlling of the dolphin upbeat. They did not obtain the equal proportion between propulsion effect of both kicking phases, but it has been suggested, that this level of skill mastering is out of the human motor abilities. Opportunities for conscious controlling of the efficiency of the upward movement are seen in the modification of the time structure of this phase. These results could be used for improving the leg-kicking performance in butterfly swimming, as well as after stars and turns.