Author(s): ARAI, H., SUGA, T.1,2, TERADA, M.2,3, KUSAGAWA, Y.2,3, KUROKI, K.1, UMEDA, M.3,4, ISAKA, T.1,2, Institution: RITSUMEIKAN UNIVERSITY, Country: JAPAN, Abstract-ID: 1958

INTRODUCTION:
Hamstring injuries are among the most common injuries in sprinting, with male sprinters showing higher incidence rates than their female counterparts [1]. Previous studies have documented non-uniform activity within hamstring muscles during sprinting in male sprinters, as assessed using T2-weighted MRI [2, 3]. Furthermore, synergistic coordination patterns within hamstring muscles measured by T2-weighted MRI may serve as useful markers reflecting injury susceptibility [4, 5]. However, the relationship between fundamental sprint performance factors and hamstring muscle activity patterns remains unclear. Therefore, this study aimed to examine whether competitive performance level and sex influence individual muscle activity and synergistic coordination patterns within the hamstring muscles during sprinting.
METHODS:
Experiment 1 included 32 male sprinters stratified by season-best 100-m time following methods described in previous studies [6, 7]: a fast group (< 11.00 s; n = 16, 10.84 ± 0.17 s) and a slow group (≥ 11.00 s; n = 16, 11.25 ± 0.21 s). Experiment 2 included 14 male and 14 female sprinters matched for competitive performance level using World Athletics scores based on their season-best 100-m times (885 ± 83 vs. 884 ± 72, respectively). All participants three 60-m sprints with 2-min recovery intervals. T2-weighted MRI was acquired before and after the sprint protocol. Individual muscle activity was quantified as the percentage change in T2. Synergistic coordination patterns were evaluated using 1) activity share, defined as the relative contribution of each muscle to total hamstring T2 change, and 2) activity proportion, defined as the coefficient of variation of the four muscles’ contributions [4]. Linear mixed-effects models and Welch’s t test were used to determine within- and between-group differences.
RESULTS:
In Experiment 1, no significant differences in individual muscle activity and synergistic coordination patterns were observed between the fast and slow groups. In Experiment 2, male sprinters showed a trend toward lower overall hamstring muscle activity compared to females (p = 0.075 for the main effect of sex), with significantly lower semimembranosus (SM) activity (p = 0.002). Activity proportion of the hamstring muscles was significantly higher in the male group compared to the female group (p = 0.002). Activity share of the SM was significantly lower in the male group compared to the female group (p = 0.012).
CONCLUSION:
Male sprinters demonstrated more asymmetrical activity patterns within the hamstring muscles than female sprinters, characterized by lower SM activity. These sex-specific coordination patterns may be one potential factor underlying the higher hamstring injury rates previously observed in male sprinters.

[1] Edouard et al. 2015. [2] Bourne et al. 2021. [3] Yoshimoto et al. 2022. [4] Schuermans et al. 2014. [5] Schuermans et al. 2016. [6] Abe et al. 2019. [7] Kumagai et al. 2000.