Risk Factors for Stress Fracture Injury in British Army Standard Entry Recruits

Abstract

Stress fracture injury during British Army Phase-1 training can lead to medical discharge. Identifying potential risk factors in relevant populations will help validate appropriate preventative measures. PURPOSE: The aim of this study was to identify the risk factors for stress fracture injury in British Army Standard Entry (SE) recruits. METHODS: Demographic, physical performance and lifestyle factors, and injury data were obtained retrospectively for SE recruits (n = 2336) entering Phase-1 training at four Army Training Regiments (ATR) between January 2002 and August 2005. The relative risk (RR, (95% confidence intervals)) of injury for each factor was tested for statistical significance using Chi-squared contingency analysis. RESULTS: There were a total of 207 (8.9%) recorded stress fracture cases, with a higher rate of stress fractures occurring at ATR Bassingbourn (Obs χ23 = 42.9, p < 0.001). Females were eight times more likely to sustain a stress fracture injury than males (Obs χ21 = 226.6, p < 0.001). Significant predictive risk factors for males included 1.5-mile runtime (RR, 3.23 (2.45-4.01); p < 0.001); static arm endurance (RR, 1.64 (1.05-2.23); p < 0.05); and number of heaves (RR, 2.15 (1.52-2.78); p < 0.001). Infemales, body mass (RR, 2.68 (1.86-3.50); p < 0.001); body mass index (RR, 2.50 (1.74-3.26); p < 0.001); percentage body fat (RR, 1.70 (1.11-2.29); p < 0.05); 1.5-mile run time (RR, 2.34 (1.60-3.08); p < 0.001); back extension strength (RR, 2.17 (1.46-2.88); p < 0.01); static lift strength (RR, 2.41 (1.65-3.17); p < 0.001); dynamic lift score (RR, 2.58 (1.82-3.34); p < 0.001); and static arm endurance (RR, 1.77(1.04-2.50); p < 0.05) were significant predictive risk factors. CONCLUSION: Male and female SE recruits are at greater risk of stress fracture injury if they enter Phase-1 training with lower aerobic fitness and body strength, indicating the importance of physical fitness for Army recruits. Females with lower body mass and those with less body fat also have a higher likelihood of sustaining a stress fracture injury. These findings might contribute towards developing appropriate countermeasures for reducing injury risk.