Allostatic Load Is Associated with Overuse Musculoskeletal Injury during US Marine Corps Officer Candidates School.

Introduction: Overuse musculoskeletal injuries (MSKI) remain a significant medical challenge in military personnel undergoing military training courses; further understanding of the biological process leading to overuse MSKI development and biological signatures for injury risk are warranted. The purpose of this study was to determine the association between overuse MSKI occurrence and physiological characteristics of allostatic load characterized as maladaptive biological responses to chronic stress measured by wearable devices in US Marine Corps officer candidates during a 10-wk training course.

Methods: Devices recorded energy expenditure (EE), daytime heart rate (HR), sleeping HR, and sleep architecture (time and percentage of deep, light, rapid eye movement sleep, awake time, total sleep). Flux was calculated as the raw or absolute difference in the average value for that day or night and the day or night beforehand. Linear mixed-effect model analysis accounting for cardiorespiratory fitness assessed the association between overuse MSKI occurrence and device metrics ( α = 0.05).

Results: Sixty-nine participants (23 females) were included. Twenty-one participants (eight females) sustained overuse MSKI. Overuse MSKI occurrence in male participants was positively associated with daytime HR ( β = 5.316, P = 0.008), sleeping HR ( β = 2.708, P = 0.032), relative EE ( β = 8.968, P = 0.001), absolute flux in relative EE ( β = 2.994, P = 0.002), absolute EE ( β = 626.830, P = 0.001), and absolute flux in absolute EE ( β = 204.062, P = 0.004). Overuse MSKI occurrence in female participants was positively associated with relative EE ( β = 5.955, P = 0.026), deep sleep time ( β = 0.664, P < 0.001), and percent deep sleep ( β = 12.564, P < 0.001) and negatively associated with absolute flux in sleeping HR ( β = -0.660, P = 0.009).

Conclusions: Overuse MSKI occurrences were associated with physiological characteristics of allostatic load, including chronically elevated HR and EE and greater time in restorative sleep stages, which may serve as biological signatures for overuse MSKI risk.