Load and Sex Impact Active Lower Limb Muscle Volume During Running

Military training requires personnel to safely dissipate large ground reaction forces to avert musculoskeletal injury. Training often requires running with heavy body borne loads, but it is currently unknown if active lower limb muscle volume increases when running with load, and whether muscle volume differs between sexes. Thirty-six (20 Male, 16 Female) participants had lower limb muscle volume quantified when running 4.0 m/s with four body borne loads (20, 25, 30, 35 kg). Custom Matlab code calculated hip, knee, and ankle muscle force (Fm=Mjoint/r) and volume (Vm= L×Fm/σ), using moment arm (r), fascicle length (L) and isometric muscle force per unit of cross-sectional area (σ=20N/cm2) data obtained from published work. Muscle volume was submitted to an RM ANOVA to test the main effect and interaction between sex (male, female) and load (20, 25, 30, 35 kg). Alpha was p \u3c 0.05. Females used greater knee muscle volume than males to run with the 20 (p=0.019) and 35 kg (p=0.017), but not 25 (p=0.280) or 30 kg (p=0.534) loads. Load increased active muscle volume increased at the ankle (p=0.012), but not hip (p=0.112) or knee (p=0.887). Sex had no effect on active muscle volume (p\u3e0.05)