Females and males use different hip and knee mechanics in response to symmetric military-relevant loads

The purpose of this study was to determine if females and males use different hip and knee mechanics when walking with standardized military-relevant symmetric loads. Fifteen females and fifteen males walked on a treadmill for 2-min at a constant speed under three symmetric load conditions (unloaded: 1.71 kg, medium: 15 kg, heavy: 26 kg). Kinematic and kinetics of the hip and knee were calculated in the sagittal and frontal planes of the dominant limb. In females, hip abduction moments (normalized to total mass) and sagittal knee excursion decreased with increased load (p ≤ 0.024). In males, hip frontal excursion and adduction angle increased with load (p ≤ 0.003). Females had greater peak hip adduction angle than males in the unloaded and medium load conditions (p ≤ 0.036). Across sex, sagittal hip and knee excursion, peak knee extension angle, and peak hip and knee flexion angles increased with increased load (p ≤ 0.005). When normalized to body mass, all peak joint moments increased with each load (p ≤ 0.016) except peak hip adduction moment. When normalized to total mass, peak hip adduction moment and knee flexion, extension, and adduction moments decreased with each load (p < 0.001). While hip frontal plane kinetic alterations to load were only noted in females, kinematic changes were noted in males at the hip and females at the knee. Differences in strategies may increase the risk of hip and knee injuries in females compared to males. This study noted load and sex effects that were previously undetected, highlighting the importance of using military-relevant standardized loads and investigating frontal plane adaptations.