In an attempt to explain how inter-stroke periodicity and velocity patterns modify the mean swimming pace in breaststroke, the swimming profiles of skilled teenage competititve breaststroke swimmers, four County and four National standard (n = 8), were recorded continuously during three independent trials at each of three different paced swims. Digitally coded on-line velocity profiles over the final 12 m of the pool length were analysed to determine intra-stroke maximum and minimum velocities, leg-arm transitional (glide) velocity, stroke period and mean stroke velocity. At all levels of pace the boys produced larger intra-stroke mean velocities (1.14 m/s), peak velocities (2.14 m/s), and shorter stroke periods (1.30 s) than the girls (1.03 mls, 2.05 mls, and 1.47 s respectively). The girls produced higher mean leg-arm transitional velocities (1.19 m/s) than the boys (1.10 m/s) and the minimum stroke velocity of all swimmers was observed to vary little with sex or pace. The arm action, building on the velocity produced by the leg action, generated the peak velocities while the recovery of the legs led to the minimum intra-stroke velocity. The duration of the leg-arm transition varied greatly, being a marked and extended discontinuity at slow speed, and a smooth transition at maximum speed. The velocity-time profile increasingly approximated to an isosceles triangle as pace increased, from which it may be postulated, on the grounds of simple geometry, that an individual swimmer exhibits a high level of swimming skill when the mean swimming velocity equals half peak velocity. Unless a swimmer introduces qualitative changes in technique, a decrease in stroke period will necessarily follow the generation of higher peak velocities. In skilled swimming the mean stroke velocity is held to be independent of stroking rate for any given peak velocity. For any given mean stroke velocity shorter stroke periods may only be achieved by cutting the stroke cycle, thereby increasing the accelerations and decelerations and hence the effort expended. Optimisation of stroke period for a given peak velocity is, therefore, important in energy conservation, making in this way its contribution to overall competitive swimming performance.
© Copyright 1992 Biomechanics and Medicine in Swimming. Swimming Science VI. Published by E & FN Spon. All rights reserved.