Recruitment Properties Of Corticospinal Excitability And Cortical Inhibition Of The Hamstring Muscles In Sprinters

PURPOSE: The neuromuscular activity in the hamstring muscles is vital for rapid force control of the lower extremities during sprint running. It has been suggested that well-trained sprinters have greater volume of hamstring muscles than non-athletes or other athletes. As sprinters usually repeat sprint running, these repeated competitive movements could lead to not only a muscle hypertrophy but also plastic changes in the central nervous system innervating the lower extremities, enabling improvement of movement-specific control. This study aimed to clarify the characteristics of corticospinal excitability and cortical inhibition of the hamstring muscles in sprinters. METHODS: A total of 10 elite sprinters and 12 control participants (recreationally active males) were included in this study. The excitability of the corticospinal pathway during isometric contractions of the biceps femoris muscle was investigated by transcranial magnetic stimulation. The stimulus intensity and amplitude of the motor-evoked potentials (recruitment curves) demonstrated a sigmoidal relationship. The maximum slope, plateau value, and threshold of the recruitment curve were calculated. Additionally, we assessed the silent period duration reflecting degree of cortical inhibition. Each parameter was compared between groups using the independent t-test. RESULTS: The maximal slope of the recruitment curve of the corticospinal excitability of the biceps femoris was significantly lower in sprinters than in control subjects (8.9 ± 4.9 vs. 16.2 ± 10.1, p = 0.049). Meanwhile, the threshold (27.3 ± 10.1 vs. 35.1 ± 15.5, p = 0.204), plateau value (395.5 ± 184.1 vs. 496.2 ± 151.5, p = 0.194), and silent period duration (113.7 ± 10.9 vs. 115.3 ± 9.7, p = 0.721) did not differ between the groups. CONCLUSION: The lower slope of the recruitment curve of corticospinal excitability in sprinters indicates that the biceps femoris muscle of sprinters is capable of gradually adjusting the motor output compared to control participants. This specific recruitment property of corticospinal excitability of the biceps femoris in sprinters can reflect the plastic change in the corticospinal pathway due to long-term sprint training. This work was supported by Academic Development Fund (Keio University Academic Development Funds).