Musculoskeletal system

Background: Breaststroke kicking is spatially more complex than other swimming styles, and a deep understanding of its motor control is particularly important for learning an effective kicking action.The methodology of mixed matrix factorization (MMF) makes it possible to simultaneously extract the kinematic and muscle synergies and to examine the role of the extracted muscle synergies in relation to the joint movements.Purpose: To analyze the motor control structure during the breaststroke kicking from the perspective of kinematic-muscle synergy as a case study.Methods: One male breaststroke swimmer performed a breaststroke kick swim in a water flume, and then the three-dimensional motion analysis and surface electromyography (EMG) measurements of the left lower limb were conducted.Using the kinematic and EMG data, the kinematic-muscular synergies were extracted using MMF algorithm.Results and Discussion: Based on the results of R 2 in the extracted synergies, the number of kinematic-muscular synergies was determined to be four.From the results of the components and active timing in the extracted synergies, it was inferred that Synergy#1 contributes to the out-sweep movement, that Synergy#2 contributes to the in-sweep movement, that Synergy#3 contributes to postural coordination during catch and glide and that Synergy#4 contributes to the recovery movement.Future work is needed to increase the sample size and to verify the validity and universality of the results in the kinematic-muscle synergies.