KNEE AND ANKLE MUSCLES COACTIVATIONS IN BREASTSTROKE SWIMMING KICK AND RECOVERY: EXPLORATORY APPROACH

The specificities of body position in breaststroke induce important lower limbs solicitations for the swimmers to propel themselves efficiently. Coactivations around the knee and ankle might appear during the powerful leg extension (i.e. push) and for leg replacement (i.e. recovery). The purpose of this exploratory study is to determine muscle activations and coactivations during these two phases at three different velocities. The EMG of four muscles was recorded (BF, RF, GAS and TA). The results showed important activations of the four muscles in the push, contrary to the recovery. However, no significant differences were found for the coactivations in the two phases and for the three velocities. These findings denoted the important resistances occasioned by aquatic environment, both in push and recovery phases, necessitating muscle coactivations to stabilise joints

Breaststroke swimmers moderate internal work increases toward the highest stroke frequencies

A model to predict the mechanical internal work of breaststroke swimming was designed. It allowed us to explore the frequency–internal work relationship in aquatic locomotion. Its accuracy was checked against internal work values calculated from kinematic sequences of eight participants swimming at three different self-chosen paces. Model predictions closely matched experimental data (0.58±0.07 vs 0.59±0.05 J kg−1 m−1; t(23)=−0.30, P=0.77), which was reflected in a slope of the major axis regression between measured and predicted total internal work whose 95% confidence intervals included the value of 1 (β=0.84, [0.61, 1.07], N=24). The model shed light on swimmers ability to moderate the increase in internal work at high stroke frequencies. This strategy of energy minimization has never been observed before in humans, but is present in quadrupedal and octopedal animal locomotion. This was achieved through a reduced angular excursion of the heaviest segments (7.2±2.9° and 3.6±1.5° for the thighs and trunk, respectively, P<0.05) in favor of the lightest ones (8.8±2.3° and 7.4±1.0° for the shanks and forearms, respectively, P<0.05). A deeper understanding of the energy flow between the body segments and the environment is required to ascertain the possible dependency between internal and external work. This will prove essential to better understand swimming mechanical cost determinants and power generation in aquatic movements