Background Strength training interventions have long been a cornerstone of ankle injury rehabilitation, with greater emphasis on the eccentric (ECC) muscle actions necessary for coordinated ankle movements. Deficits in strength between involved and uninvolved ankles typically exist following an acute ankle sprain; while these same deficits have also been implicated as a contributing factor to the development and persistence of chronic ankle instability (CAI).

Objective To compare ECC isokinetic ankle strength measures between athletes with and without CAI after a history of unilateral ankle sprain.

Design Cross-sectional.

Setting Athletic training research laboratory.

Participants A total of 135 male and female student-athletes participating in the high risk sports of football, basketball, lacrosse, soccer, field hockey, and volleyball with histories of unilateral ankle sprain.

Interventions The independent variables were group classification (CAI, stable) and limb (involved, uninvolved). Subjects completed the Cumberland Ankle Instability Tool (CAIT) to define group classification with subjects scoring <25 being classified as CAI and those scoring >25 being classified as stable.

Main outcome measurements ECC isokinetic peak torque (PT) values were collected using a KinCom isokinetic dynamometer during plantar flexion (PF), dorsiflexion (DF), inversion (INV), and eversion (EV) and movements at both 30˚/s and 120˚/s.  2 × 2 ANOVAs were used to compare group (CAI, stable) and limb (involved, uninvolved) for each dependent variable.

Results A significant main effect was present for ECC INV at 30˚/s (p = 0.033). The uninvolved side (26.9 ± 10.9 Nm) was stronger than the involved side (25.3 ± 9.6 Nm). A trend towards significance existed for the ECC PF, with the uninvolved side appearing to be stronger at 30˚/s (229.9 ± 74.5 Nm, p = 0.095) and 120˚/s (218.4 ± 7 9.8 Nm, p = 0.106) than the involved limb (30˚/s = 223.8 ± 82.4 Nm; 120˚/s = 207.3 ± 82.0 Nm). A similar trend was observed when examining ECC INV values at 120˚/s (p = 0.100) and ECC DF at 120^˚/s (p = 0.098). Interestingly, there were no significant differences between any of the group comparisons.

Conclusions ECC ankle strength does not differentiate whether an athlete has CAI, but the musculature on the involved ankle appears to be weak compared to the opposite uninvolved limb. Our results add to the growing evidence suggesting that neuromuscular deficits other than strength are likely producing the chronic signs and symptoms associated with CAI.