Pacing the phasing of leg and arm movements in breaststroke swimming to minimize intra-cyclic velocity fluctuations

Abstract

In swimming propelling efficiency is partly determined by intra-cyclic velocity fluctuations. The higher these fluctuations are at a given average swimming velocity, the less efficient is the propulsion. This study explored whether the leg-arm coordination (i.e. phase relation ϕ) within the breaststroke cycle can be influenced with acoustic pacing, and whether the so induced changes are accompanied by changes in intra-cyclic velocity fluctuations. Twenty-six participants were asked to couple their propulsive leg and arm movements to a double-tone metronome beat and to keep their average swimming velocity constant over trials. The metronome imposed five different phase relations ϕi (90, 135, 180, 225 and 270°) of leg-arm coordination. Swimmers adjusted their technique under the influence of the metronome, but failed to comply to the velocity requirement for ϕ = 90 and 135°. For imposed ϕ = 180, 225 and 270°, the intra-cyclic velocity fluctuations increased with increasing ϕ, while average swimming velocity did not differ. This suggests that acoustic pacing may be used to adjust ϕ and thereby performance of breaststroke swimming given the dependence of propelling efficiency on ϕ.

Fig 1. An exemplary velocity profile of a breaststroke cycle.

The profile clearly exhibits intra-cyclic velocity variations, i.e. pronounced deviations from the average swimming velocity $\overline{v}$, as represented by the horizontal line. The characteristic points from Eqs 3 and 2 are indicated as local maxima and minima in the velocity profile. The profile was obtained by averaging 7 consecutive breaststroke cycles from one individual measured with automated LED tracking on a normalized time-scale. The standard deviation is indicated by the dashed lines, reflecting inter-cyclic variations. Note that in this trial the leg-arm phase coordination was around 210°.

Fig 2. Setup for velocity tracking of the LED marker.

Top view of the swimming pool with the synchronized cameras placed in the side wall of the pool. The cameras (at 35, 40 and 45 m) recorded the swimmer’s motion, using a LED marker on the hip.

Fig 3. Executed phase relation ϕ_e.

(a) Mean ${\overline{\varphi }}_e$ as a function of the imposed phase relation ϕ_i. The grey dashed lines are the line of identity and the mean preferred phase relation ${\overline{\varphi }}_p$ respectively. The shaded area represents the standard deviation from the ${\overline{\varphi }}_p$. (b) Intra-individual standard deviation σ_ϕ as a function of ϕ_i. Standard deviations are indicated by the vertical bars. (c) Typical mean velocity profiles for three different ϕ_i obtained from one participant.

Fig 4. Effects of imposed phase relation ϕ_i on mean velocity v¯ (a), intra-cyclic velocity fluctuations IVV (b) rate of perceived exertion RPE (c) and rate of perceived difficulty D_ϕ (d).

Vertical bars represent the standard deviation.