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 (MSKIs) 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 (HRmean, HRmin, HRmax), physical activity energy expenditure (PAEE), metabolic equivalent (METmean)) 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 (+1259.70 g·min-1, p < 0.001), average intensity (+7.20 g, p < 0.001), bone stimulus (+126.73 A.U., p < 0.001), high-g steps (+559.34 g, p < 0.001), HRmin (+13.15 bpm, p < 0.001), HRmean (+28.79 bpm, p < 0.001), HRmax (+16.95 bpm, p < 0.001), and METmean (-1.93 kcal·kg-1·h-1, p < 0.001) were higher during the endurance course than ruck; step count (-14934, 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 ruck, and PC3 (p < 0.01) for endurance course revealing greater demands in 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.