Wearable-Assessed Biomechanical and Physiological Demands during Load Carriage and Tactical Mobility Tasks among Male and Female Military Personnel

Purpose: Load carriage and tactical mobility are military tasks that pose significant risks for musculoskeletal injuries (MSKI) in military personnel. This investigation compared biomechanical and physiological demands of a load carriage and tactical mobility task and examined their differences between sexes using reliable and validated wearables among United States Marine officer candidates. Methods: Forty-one candidates (16 women) performed a 15.8-km loaded ruck march and a 4.0-km endurance course that assessed load carriage and tactical mobility performance, respectively. Inertial measurement units on the distal tibia and wrist-worn watches collected biomechanical (total step count, impact load, bone stimulus, average intensity, low-/medium-/high-g step count) and physiological (heart rate (HR_mean, HR_min, HR_max), physical activity energy expenditure (PAEE), and metabolic equivalent (MET_mean)) data. Paired sample t-tests compared metrics between events. Principal component (PC) analyses interpreted event demands. Independent samples t-tests analyzed sex differences between PCs (α = 0.05). Results: Impact load (+1259.70g·min⁻¹ , P < 0.001), average intensity (+7.20g, P < 0.001), bone stimulus (+126.73 AU, P < 0.001), high-g steps (+559.34g, P < 0.001), HR_min (+13.15 bpm, P < 0.001), HR_mean (+28.79 bpm, P < 0.001), HR_max (+16.95 bpm, P < 0.001), and MET_mean (−1.93 kcal·kg⁻¹ ·h⁻¹ , P < 0.001) were higher during the endurance course than the ruck; step count (−14,934, P < 0.001) and PAEE (−713 kcal, P < 0.001) were lower. Three PCs explained 84.3% and 81.5% of variance for the ruck and endurance course. PC1 represented biomechanical variables, PC2 physiological variables, and PC3 g step count. Sex differences were found in PC2 (P = 0.039) and PC3 (P = 0.002) for the ruck, and PC3 (P < 0.01) for the endurance course revealing greater demands on women. Conclusions: Tactical mobility requires greater biomechanical and physiological demands than load carriage and places greater demands on women. Task and sex-specific training strategies may improve performance and mitigate MSKI risk.