Association Between Ankle Sprains and Functional Performance During Infantry Training: A Prospective Cohort Study.

BACKGROUND: The execution of demanding military tasks relies on high levels of functional performance. Training-related ankle sprains may be associated with impaired operational capabilities. The aim of this cohort study was to examine the association between lateral ankle sprains sustained during army basic training and the longitudinal functional trajectories of recruits over 5.5 months. MATERIALS AND METHODS: New recruits (initial enrollment n = 365) were assessed at baseline (T0), 3 months (T1), and 5.5 months (T2). Assessments included perceived ankle instability (Cumberland Ankle Instability Tool), dynamic balance (Y-Balance Test), agility (Hexagon test), calf muscle strength (Heel Raise test), proprioception (Active Movement Extent Discrimination Assessment), and a 3,000 m run. Clinical sprain diagnoses were recorded during the first 3 months. The primary analysis utilized a complete-case approach, while missing data because of cohort attrition was handled via a Linear Mixed Model (LMM) sensitivity analysis. RESULTS: Because of administrative and medical attrition, 186 recruits were lost to follow-up (51.0% attrition). The analyzed complete-case cohort comprised 179 male recruits (ages 18-21), with 52 participants (29.0%) diagnosed with an ankle sprain. Significant time × sprain interactions were observed for agility, calf strength, dynamic balance, and perceived ankle instability (all P < .01). The NO-SPRAIN group consistently improved in functional performance from T0 to T1 and largely maintained these gains through T2. For example, the NO-SPRAIN group demonstrated increased calf strength from T0 to T1 (mean difference [MD]: -34.9, 95% CI: [-49.0 to -20.8], Cohen's d: -0.92), whereas the SPRAIN group showed no improvement (MD: 6.9, 95% CI: [-13.3 to 27.1], Cohen's d: 0.18). Conversely, the SPRAIN group demonstrated functional decline or no change alongside significantly increased perceived instability from T0 to T1 (MD: 5.8, 95% CI: [3.7 to 7.9], Cohen's d: 1.16). When controlling for prior injury history and BMI, proprioceptive differences between groups lost statistical significance. No significant interactions were found for the 3,000 m run. CONCLUSIONS: Sustaining an ankle sprain early in infantry training was associated with persistent functional deficits relevant to operational readiness. These functional disparities over 5.5 months highlight the need to evaluate and implement targeted rehabilitation and prevention programs within military training regimens. LEVEL OF EVIDENCE: II.