To compare two methods of ankle evertor muscle reinforcement after ankle sprain: concentric vs eccentric reinforcement. Eighteen subjects practising sport with first episode of ankle sprain. The first randomized group underwent conventional physical therapy including concentric reinforcement of the evertor ankle muscles [concentric group (CG)]. The second randomized group underwent eccentric reinforcement [eccentric group (EG)]. At the end of the physical therapy, the strength of the evertor muscles was tested using an isokinetic dynamometer. The measurements were peak torques in the concentric and eccentric modes; ankle strength deficits, expressed as percentages of the healthy ankle values recorded in the concentric and eccentric modes; ratios between concentric/eccentric values. After the concentric reinforcement, in the CG group, there is both significant concentric strength deficit and an eccentric strength deficit on the injured side in comparison with the healthy side. After the eccentric reinforcement in the EG group, the muscle strength was significantly greater during concentric movements. Eccentric rehabilitation therefore restored the strength of the injured evertor muscles. These results show the value of this method, especially as the weakness of these muscles after sprains is one of the main risk factors contributing to instability and the recurrence of sprains.