Performance Asymmetry, the Risk for Ankle Sprain, and the Influence of an Intervention Program in New Male Infantry Recruits

<b>Background</b>: Functional performance interlimb asymmetry may increase the risk of ankle sprains during basic military training. We aimed to (1) evaluate interlimb balance, agility, and ankle instability asymmetry in soldiers in infantry training as a risk factor for acute ankle sprains; (2) evaluate the effect of ankle sprains and sprain prevention exercise program on performance asymmetry. <b>Methods</b>: Newly inducted infantry soldiers were recruited from two induction cycles (intervention [INT] <i>n</i> = 365, control [CON] <i>n</i> = 421). Participants were assessed at the beginning of infantry basic training (T0) and after four months (T1) for anthropometrics, balance, agility, and perceived ankle instability, and were monitored for ankle sprains (SPRAIN/NO-SPRAIN). The INT group performed an ankle sprain prevention program 5 days/week × 5 min/day. <b>Results</b>: at T0 there were differences in interlimb asymmetry in Cumberland Ankle Instability Tool (CAIT) in SPRAIN soldiers in both groups (<i>p</i>-value < 0.001), and differences between the groups in Hexagon, Y-Balance Test (YBT) and CAIT (<i>p</i>-values 0.007, 0.002, 0.002, respectively). There was a decrease in interlimb asymmetry in Hexagon and YBT for SPRAIN soldiers in the INT group, and an increase in CAIT asymmetry in SPRAIN soldiers in both groups. Stepwise logistic regression did not find predictors for ankle sprains during training. <b>Conclusions</b>: The intervention program reduced interlimb asymmetry in balance and agility for soldiers who sprained their ankle during training. In these soldiers, CAIT asymmetry increased during training regardless of the intervention. Ankle sprain intervention programs should be implemented to reduce interlimb asymmetries in functional abilities and reduce the risk of injury.