Adding muscle where you need it: non-uniform hypertrophy patterns in elite sprinters

Area of Science:

• Biomechanics
• Human Physiology
• Sports Science

Background:

• Elite sprinters exhibit superior gait velocity and acceleration compared to average humans.
• Muscle forces are crucial for sprint performance, but lower limb muscle volume distribution in sprinters remains understudied.

Purpose of the Study:

• To investigate the distribution of lower limb muscle volumes in elite sprinters using in vivo MRI.
• To compare muscle sizes between sprinters and non-sprinters, assess asymmetry, and identify gender differences.

Main Methods:

• Utilized non-Cartesian Magnetic Resonance Imaging (MRI) to quantify in vivo muscle volumes in 15 NCAA Division I sprinters.
• Normalized muscle sizes by body size and calculated Z-scores to identify non-uniform muscle hypertrophy.
• Assessed bilateral symmetry and gender-specific differences in muscle size.

Main Results:

• Sprinters displayed 22% greater overall limb musculature relative to height-mass compared to non-sprinters.
• Significant hypertrophy was observed in hip- and knee-crossing muscles (30% larger on average) but not uniformly across all lower limb muscles.
• The tibialis posterior muscle was significantly larger (28%) in sprinters, while population-wide asymmetry was not significant, though individual asymmetries exceeded 15%.

Conclusions:

• Elite sprinting performance is associated with non-uniform muscle hypertrophy, particularly in hip and knee flexors and extensors.
• These specific muscle adaptations, rather than uniform growth, appear advantageous for achieving maximal sprint speeds.
• Normalized muscle sizes did not show significant gender differences in this cohort of elite sprinters.