Author(s): TAKAHASHI, K., FUJII, N., MIKOSHI, T., KAWAMA, R., NAKAMURA, Y., WAKAHARA, T., Institution: DOSHISHA UNIVERSITY, Country: JAPAN, Abstract-ID: 1788

INTRODUCTION:
Human muscles exhibit a disproportionately larger physiological cross-sectional area (PCSA ∝ force potential) but a shorter fascicle length (∝ speed/excursion potential), as compared to apes [1]. This unique architectural profile can reflect our adaptation to good endurance runners but poor sprinters in the evolutionary process. A fundamental question is how such an endurance-oriented basic design is optimized to achieve a faster running speed in humans. While the relevance of apparent muscle size (e.g., volume) in sprint performance has been extensively examined, less is known about the architecture that provides closer insights into muscle function. Here, we performed 3D architectural analyses of the entire lower limb with diffusion tensor MR imaging to unveil the relationship between muscle architecture and sprint running performance in humans.
METHODS:
For 20 male sprint runners, the MR scanning of the whole lower limb was conducted using the diffusion tensor imaging and DIXON sequences. For a total of 30 lower limb muscles, 5000 fascicles per muscle were automatically reconstructed in 3D space, and their fascicle lengths and PCSAs (volumes divided by fascicle lengths) were quantified, partly following previous works [2,3] in combination with deep learning-based semi-automatic segmentations. Also, participants performed a 100-m sprint run with their maximal efforts, and their maximal running speed was measured. The relationship between muscle (group) architecture and running speed was tested with Pearson’s correlation analysis.
RESULTS:
Total PCSA of the hip muscles was positively correlated with the maximal running speed (r = 0.485, p = 0.030), whereas their mean fascicle length did not. Neither the PCSA nor the fascicle length of the thigh or shank muscles was correlated with the maximal running speed. Among the hip muscles, only the gluteus maximus showed a significant positive correlation between the PCSA and the maximal running speed (r = 0.584, p = 0.007). This remained significant when the PCSA was normalized to two-thirds power of body mass (r = 0.530, p = 0.016).
CONCLUSION:
Faster sprint runners had a larger PCSA rather than longer fascicle length in the gluteus maximus, the biggest muscle playing a critical role in human sprinting [4], potentially prioritizing its force rather than speed/excursion potential to achieve higher running speeds. These findings widely extend our understanding of the morphological underpinnings of human sprint performance, which is so far limited to the muscle size level. Although human muscles are basically characterized by disproportionately large PCSA and likely optimized for endurance running, further enlargement of a specific muscle’s PCSA may rather be beneficial for high-speed running.
REFERENCES:
[1] Payne et al. 2006 J. Anat.
[2] Takahashi et al. 2025 J. Biomech.
[3] Takahashi et al. 2025 J. Appl. Physiol.
[4] Dorn et al. 2012 J Exp. Biol.