Average swimming speeds for 6 sections of the 50-meter backstroke race: Comparison of performance in zones swum underwater or at the surface in 12 international short course events

We measured the speed of 12 international-level swimmers (6♀ and 6♂) for 6 sections of the 50m backstroke race in a short course (25m) pool (0-5m; 5-15m; 15-25m; 25-30m; 30-40m; 40-50m) by breaking down the races using video analysis. Our assessment revealed that swimmers went faster when underwater (independently of the benefit obtained by pushing off the pool wall in the 0-5m and 25-30m zones) than when they swam at the surface. These results were supported by the per-zone speed ranking established by the vast majority of 151 sports students acting as observers. The latter viewed each race 3 times, in order to divide up the race into the 6 zones using frame-by-frame images (with an index of agreement of more than 76%, according to Pareto's criterion). Only the per-zone speed rankings for the 3 slowest female swimmers deviated from the majority ranking (using Kendall's L statistic), as the result of a shorter underwater segment during the 2^nd length.

Despite being considered (by the sport's rules and in scientific terms) as a subsidiary and disruptive element of propulsion, underwater dolphin kicks are responsible for the highest speeds in this type of event.