Breathing and propelling in crawl as a function of skill and swim velocity.

This study analyzes apnea (A), exhalation (E), and inhalation (I) duration with respect to stroke organization in front crawl as a function of inhalation side, swim velocity and performance level. Thirty-six male subjects comprised two groups based on performance level: more expert (ME) and less expert (LE) swimmers. All swam with one inhalation per cycle to the preferred side at speeds corresponding to two specific race paces: 100-m (V100) and 800-m (V800) velocities. The breathing arm (BA) is located on the inhalation side, and the non-breathing arm (NBA) on the opposite side. The sound of air passing in and out of the swimmers' mouths was captured by a microphone and synchronized with video frames. Stroke phases and arm coordination were identified by video analyses. Arm coordination was quantified using two indices of coordination (IdC) corresponding to the lag time between the beginning of the BA (IdC-BA) or NBA (IdC-NBA) propulsive action and the end of that of the other arm. As velocity increases, the ME are observed to reduce I during BA recovery (-19.4 +/- 31.6 %, p < 0.05) while the LE increase A (+ 34.8 +/- 25.2 %, p < 0.05) during BA entry, catch and recovery and NBA pull and push. These variations are related to a lengthening of the pull for both arms at the expense of BA non-propulsive phases. At V100, the ME have greater E (p < 0.05) during BA entry and catch (+ 21.1 +/- 38.2 %) and NBA push (+ 26.3 +/- 39.5 %) compared to the LE. This increase, at the expense of A, corresponds to a shorter BA push and NBA recovery. At V800, the ME exhibit a longer A (p < 0.05) during BA recovery (+ 19.9 +/- 33.2 %) and NBA pull (+ 24.2 +/- 31.5 %), and decreased I during NBA push and pull. These differences are related to a shortening of BA recovery and pull and a longer push for both arms. These breath and stroke adaptations correspond to an increase in stroke rate and IdC-BA with the velocity and performance level. This study points out the breathing-propelling aspects of coordination that indicate technical skill in swimming.