Determinants of physiological demands, physiological resilience, and muscle fatigability during load carriage in women: an observational trial.

PURPOSE: Since the UK Armed Forces opened all combat roles to women in 2018, more female soldiers are carrying heavier loads for longer. This study investigated associations between aerobic capacity, strength, and lean mass and the demands of load carriage in women, and associations between load carriage demands and muscle fatigability. METHODS: Thirty-nine women (28 ± 4 y) had maximal rate of oxygen uptake (V̇O2max) and lean mass assessed before completing load carriage (12.8 km in 120 min carrying 20 kg). Oxygen uptake (%V̇O2max), heart rate (HR), and ratings of perceived exertion (RPE) were measured during load carriage. Isometric and isokinetic (60 and 180°·s-1) peak knee flexor and extensor torque were measured before and after load carriage. Physiological resilience was determined from decoupling between internal (V̇O2 and HR) and external (pace) workload over time. RESULTS: Higher V̇O2max was associated with lower %V̇O2max and RPE, and higher HR decoupling during load carriage (R2 ≤ 0.23; p ≤ 0.042). Higher lean mass and isometric knee extensor strength were associated with lower RPE during load carriage (R2 ≤ 0.18; p ≤ 0.042). Fatigue resistance of the knee extensors was observed, with only isometric knee flexion impaired after load carriage (-8%; p < 0.001). Higher %V̇O2max and HR decoupling during load carriage were associated with a greater reduction in isokinetic (180°·s-1) flexion peak torque (R2 ≤ 0.36; p ≤ 0.025). CONCLUSIONS: Aerobic capacity, lean mass, and knee extensor strength are potential targets in interventions to develop load carriage capacity in women.