Bone health in adults with non-ambulatory neuromuscular disorders: scoping review of risk factors, diagnosis and management.

Life in the military (e.g. Army, Air Force and Navy) is demanding. The role of military personnel varies by nation, branch of the military, specific role and level of rank (among other factors), but all must be prepared for a range of tasks, including wartime deployments, peacekeeping and disaster relief []. Tasks often involve strenuous physical activity, including combat engagement, marching, digging and marksmanship, which at times are performed under high cognitive and physical demands (e.g. sleep deprivation). A critical part of these tasks is movement, which often occurs while carrying significant loads (e.g. a pack with food, water, ammunition and other survival equipment) and operating in stressful environments. In particular, heavily loaded marching is commonplace and taxing; for example, soldiers deployed in Afghanistan carried a mean load of 57 kg []. As personnel must be mentally and physically fit for service, the military strives to maintain strict physical fitness standards. Initial military training (IMT), often referred to as recruit training, boot camp or basic training, is a mandatory high-intensity course typically lasting 6–14 weeks []. It is designed to turn civilians into military personnel, serving to improve occupation-specific skills, physical readiness and discipline. While the training regimen and demands of these courses may differ significantly, they are all designed to physically and mentally challenge recruits, with sleep deprivation, caloric deficits, load carriage and psychological stress to prepare them for potentially extreme situations. Research shows that improved cardiorespiratory fitness reduces the physical strain of military personnel and enhances recovery between activities []. Furthermore, higher levels of fitness are also closely linked to subsequent performance in specific operational tasks [–] and help to reduce injury risk [–]. It is well documented that initial military training increases cardiorespiratory fitness [], but also features a high prevalence of injuries [, ], which often result in high levels of attrition and financial burden []. This is in part due to the predominantly high endurance-based load of training [, ], exposing recruits to high physical stressors with little to no preparation. This is heightened by the modern recruit’s increasingly sedentary lifestyle before entry [–]. Recruits also face significant cognitive load in addition to physical training stressors []. Furthermore, during IMT, there is often inadequate energy consumption [] or time allowed for recovery, with research identifying that up to 85% of recruits are underslept [], which is of concern as Belenky et al. [] have noted that 8 h of sleep is optimal, with just 1 h less causing declines in cognitive performance. Giles et al. [] found that higher loads were most strongly associated with declines in cognitive function and increased perceived exertion [], aligning with recent systematic research indicating that the effect was greater in female recruits [, ], who are at a significantly greater risk of injury than males [, ]. Accordingly, an understanding of why these sex-based differences might occur is critical for maintaining an effective military force by mitigating potential risk. Combined, these factors create a perfect storm for fatigue, which is a performance loss from poor sleep, stress or exertion and can be split into central (neural drive) and peripheral (motor control) types [, ]. Although distinct, they often overlap: central issues like sleep loss impair physical performance [], while peripheral exertion rarely causes central fatigue. This complexity makes them hard to isolate, yet both consistently degrade vital reaction times, marksmanship accuracy, strength and vertical jump performance [, ]. While the effects of fatigue may be deliberately imposed at times, there is a clear lack of individualised periodisation or intervention targeting the effects of fatigue and the subsequent predisposition to injury that recruits may face if it is left unmanaged [].