Author(s): FUJII, N., TAKAHASHI, K., MIKOSHI, T., KAWAMA, R., WAKAHARA, T., Institution: DOSHISHA UNIVERSITY, Country: JAPAN, Abstract-ID: 2586

INTRODUCTION:
Sprint running requires rapid leg swings. The angular acceleration of the leg is determined by the torque exerted by the hip muscles and the moment of inertia (MoI) about the hip joint. From the perspective of torque exertion, many studies have examined the characteristics of muscle volume in sprinters [1, 2]. Meanwhile, greater muscle volume entails an increase in MoI. At the segment level, male sprint runners have larger muscle mass than untrained controls without a proportional increase in MoI [3], implying a specialized muscle mass distribution. However, less information is available regarding the muscle MoI and its effect on the relationship between muscle volume and sprint running performance. Thus, we examined the association between the muscle volume relative to MoI of 31 lower limb muscles and sprint running performance, including kinematic variables.
METHODS:
The axial MR images of the whole limb were acquired in the prone position in 18 male sprint runners. The volume of 31 lower limb muscles was determined from the MR images with semi-automatic segmentation using a deep learning method. The MoI of individual muscles about the hip joint was calculated from muscle volume and its radius of gyration in the sagittal plane [4]. Participants performed a 100 m maximal sprint run. The running velocity and swing velocity of the leg (line connecting the greater trochanter and the lateral malleolus) were determined from recorded video (240 fps) at the 50–60 m interval. Pearson’s correlation analysis was used to examine the relationships between measured variables.
RESULTS:
The running velocity was correlated with the maximum velocity of forward leg swing (r = 0.584, p = 0.011). This swing velocity was positively correlated with hip flexor muscle volume (r = 0.482, p = 0.045), suggesting its contribution to forward leg swing. However, the maximum velocity of forward leg swing did not correlate with the MoI of the whole leg, thigh, or shank muscles. When the hip flexor muscle volume was normalized to the MoI of the triceps surae or the medial gastrocnemius, its relation to the maximum velocity of forward leg swing became stronger (r = 0.536, p = 0.024 and r = 0.548, p = 0.020, respectively) than in the case of muscle volume alone.
CONCLUSION:
The present results suggest that larger hip flexor volume relative to MoI of the distal muscles, such as the triceps surae, enables rapid forward leg swing, thereby achieving a high running velocity. Training programs designed to attenuate hypertrophy of the triceps surae, while strengthening the hip flexors, may be advantageous for enhancing sprint running performance.
REFERENCES:
1) Handsfield et al. Scand J Med Sci Sports (2017)
2) Miller et al. Med Sci Sports Exerc (2021)
3) Sado et al. Med Sci Sports Exerc (2023)
4) Takahashi et al. J Biomech (2024)