Effects of Cycling-induced Fatigue on Lower Extremity Muscles Synergy in Novice Triathletes

The study of muscle synergy is a new method to evaluate the function of the control system of the human body. Due to the physical demands of the nature of triathletes it appears that triathletes are affected by variety degrees of muscle fatigue. The aim of this study was to determine the effect of fatigue on lower limb muscles synergy in novice triathletes. Sixteen male novice triathletes participated in this semi-experimental study. Electromyography activity of rectus femoris, vastus medialis, vastus lateralis, biceps femoris, semitendinosus, gastrocnemius medial, soleus and tibialis anterior muscles were recorded before and after the cycling-induced fatigue protocol during running task. Non-negative matrix analysis algorithm approach was used to extract muscle synergies from electromyography signals. Pearson correlation method was emplyoed to measure the similarity of the extracted patterns. Paired-sample t-test was employed to compare the relative weight of muscles before and after the fatigue protocol (P<۰.۰۵). After muscle fatigue, the first and second synergy patterns showed high similarity and the third and fourth synergy patterns showed moderate similarity.  The relative weight of vastus lateralis muscle (P=۰.۰۱۲) and tibialis anterior (P=۰.۰۲۴) decreased significantly after muscle fatigue. The relative weight of semitendinosus (P=۰.۰۱۶) and soleus (P=۰.۰۳۱) muscles increased significantly after muscle fatigue. The number of four muscle synergies were obtained by variance accounted for method from electromyography activity data of muscles before and after muscle fatigue. Cycling-induced fatigue can affect the organized cooperation of the central nervous system to create synergy patterns in triathletes during running. It seems that disruption of synergy patterns and relative weight of lower limb muscles due to cycling-induced fatigue can change the mechanics of subsequent running in triathletes and increase the possibility of injury among these individuals.