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

Abstract

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. 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). Impact load (+1259.70 g ·min -1 , P < 0.001), average intensity (+7.20 g , P < 0.001), bone stimulus (+126.73 AU, P < 0.001), high- g steps (+559.34 g , 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. 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.