Adding Muscle Where You Need It

Abstract

PURPOSE: To determine which, if any, of 35 lower limb muscles are significantly larger among competitive collegiate sprinters compared to healthy non-sprinter controls, which muscles are bilaterally asymmetric in sprinters, and which muscles are larger among male compared to female sprinters. METHODS: We used an advanced, non-Cartesian MRI sequence to rapidly acquire stacks of axial 2D images through the lower limb in competitive collegiate sprinters. We segmented 35 lower limb muscles in image sets and determined volumes, lengths, and physiological cross sectional areas of athletes’ muscles and normalized muscle measurements by the metrics of height and mass. Using a previously published dataset of healthy, non-sprinter muscle sizes, we computed Z-scores of athletes’ muscle sizes and made statistical comparisons between groups. RESULTS: Sprinters present larger muscles per height-mass than controls, but not all muscles are uniformly larger among athletes. Muscles involved in hip flexion and extension and knee extension were disproportionately and significantly larger among the sprinters than muscles crossing the ankle joint. No muscles were significantly bilaterally asymmetric among sprinters and no muscles were significantly different between male and female sprinters when normalized by the height-mass product of the sprinter. CONCLUSION: The fact that sprinters’ muscles are larger but not all uniformly larger than controls suggests that sprinters utilize muscles disproportionately in training for their sport. Hip flexion/extension and knee extension may be more important for generating high-speed gait than ankle plantarflexion and dorsiflexion. Furthermore, these data may be used as more accurate estimates of sprinters’ muscle sizes than previous data generated from cadaver dissection.