Background Tibial stress fractures (TSFs) cause a significant burden to Royal Marines recruits. No prospective running gait analyses have previously been performed in military settings.

Aim We aimed to identify biomechanical gait factors and anthropometric variables associated with increased risk of TSF.

Methods 1065 Royal Marines recruits were assessed in week 2 of training. Bilateral plantar pressure and three-dimensional lower limb kinematics were obtained for barefoot running at 3.6 m/s, providing dynamic arch index, peak heel pressure and lower limb joint angles. Age, bimalleolar breadth, calf girth, passive hip internal/external range of motion and body mass index (BMI) were also recorded. 10 recruits who sustained a TSF during training were compared with 120 recruits who completed training injury-free using a binary logistic regression model to identify injury risk factors.

Results 4 variables significantly (p<0.05) predicted increased risk of TSF (ORs and 95% CI): smaller bimalleolar width (0.73, 0.58 to 0.93), lower BMI (0.56, 0.33 to 0.95), greater peak heel pressure (1.25, 1.07 to 1.46) and lower range of tibial rotation (0.78, 0.63 to 0.96).

Summary Reduced impact attenuation and ability to withstand load were implicated in tibial stress fracture risk.