Association between Muscle Synergy and Stability during Prolonged Walking

[Purpose] The purpose of this study was to examine whether changes in muscle synergycould affect gait stability or muscle activity by comparing muscle activity before andafter prolonged walking. [Subjects and Methods] Twelve healthy male subjects walked on atreadmill for 10 min as a warm-up. Data were recorded from the participants during thefirst and last 1 min during 90 min of walking at 4.5 km/h. Electromyographic (EMG)activity was recorded for 7 leg muscles, and patterns of coordination were determined byprincipal component analysis (PCA). The patterns of activity within the anatomic musclegroups were additionally determined by repeating PCA. iEMG was calculated using the meanEMG for each cycle step during the 1 min walking periods. The largest Lyapunov exponentwas calculated to quantify each subject’s inherent local dynamic stability. [Results] Thepatterns for each of the 7 muscles showed no change between the start and end periods.However, the end period showed a higher co-activation of the triceps surae, lower iEMG ofthe medial gastrocnemius, and a smaller largest Lyapunov exponent of the mediolateral andanteroposterior directions than those observed during the start period. [Conclusion] Theincrease in triceps surae co-activation may be associated with gait stability.Key words: Muscle synergy, Muscle activity, Gait stability