Long Ground Contact Time Enhances Running Economy at High-Intensity Running

Abstract

Running economy (RE) determines the difference in distance running performance in highly-trained runners. Studies have highlighted RE importance during high-intensity running. Although RE is related to ground contact time (Tc), the relationship between RE at high-intensity running and Tc is not elucidated. It is also unclear whether the hamstrings muscle, which contribute to high-intensity running, affect RE and Tc. PURPOSE: We aimed to clarify the relationships among RE, Tc at intensity below and above the lactate threshold (LT) run, and hamstring muscle’s cross-sectional area in highly-trained long-distance runners. METHODS: We enrolled 11 highly trained male distance runners (IAAF score: 1038 ± 48). They underwent treadmill running test to assess the LT, and RE. RE was evaluated at 270 (RE270) and 360 m/min (RE360) as the intensity below and above the LT, respectively. Tc was also valuated at the same velocity (Tc270; Tc360). Both medial and lateral hamstring muscles’ cross-sectional areas (MHA and LHA, respectively) were calculated using MRI at 50% position of the right thigh. RESULTS: The subjects’ LT, RE270 and RE360 were 337 ± 17 m/min, 0.90 ± 0.08 kcal/ kg/km, and 1.00 ± 0.07 kcal/kg/km, respectively. The Tc270, Tc360, MHA and LHA values were 195 ± 17 ms, 164 ± 9 ms, 1.24 ± 0.18 cm2/kg0.67, and 0.99 ± 0.11 cm2/kg0.67, respectively. RE270 showed a significant relationship with Tc270, MHA, and LHA (r = -0.81, 0.75, and 0.60, respectively; P < 0.05), but no relationship was noted with IAAF score (r = -0.55; P = 0.08). Tc270 was related to MHA and LHA (r = -0.63 and -0.67; P < 0.05). Although RE360 showed a significant relationship with IAAF score, Tc360, and MHA (r = -0.73, -0.65, and 0.69, respectively; P < 0.05), no relationship was noted with LHA (r = 0.35; P = 0.30). Tc360 did not exhibit any significant relationship with MHA (r = -0.55; P = 0.08) and LHA (r = -0.52; P = 0.10). CONCLUSION: The findings of this study are as follows: (a) RE at high rather than low intensity is related to running performance; (b) longer Tc enhances RE; (c) superior RE and long Tc at low intensity are related to small hamstring muscles, but these associations disappear, except between RE and MHA, at high intensity. These results suggest that long Tc at high-intensity contributes to superior RE, but not to hamstring muscles, and leads to higher running performance.