PURPOSE: The purpose of this study is to verify the effect of soft tissue stiffness on joint range of motion and athletic performance in soccer players.METHODS: Fifteen adult male soccer players participated in the study. After the warm-up, calf muscle and Achilles tendon stiffness were measured. Subsequently, range of motion of the ankle joint and 30 m sprint and vertical jump were performed. Exercise performance was assessed as a field test to create an experimental environment similar to that of actual training and competition.RESULTS: Achilles tendon stiffness showed a significant correlation with the 30 m sprint and the vertical jump (<i>p</i><.05). A moderate correlation was observed between the 30 m sprint and the vertical jump(<i>p</i><.01). Soleus muscle stiffness was significantly correlated with the 30 m sprint(<i>p</i><.05). No other correlations were observed.CONCLUSIONS: Therefore, it was confirmed that Achilles tendon stiffness affects exercise performance. In a follow-up study, it was necessary to confirm the effect of the stiffness of various soft tissues on exercise performance.