Isometric and isotonic exercises are good for strengthening weak ankles, according to the American Orthopaedic Foot and Ankle Society. Isometric exercises are performed by pushing against a fixed object with the ankle, while isotonic exercises involve using the ankle's range of motion.
According to the AOFAS, the easiest ankle strengthening exercises to begin with are isometric exercises. Eversion isometrics is performed by placing the outside of the foot against a fixed object. Push outward with the foot into the object to contract the muscles within the ankle. Hold the contraction for 10 seconds.
Inversion isometrics is performed by placing the inside of the foot against a fixed object, notes the AOFAS. Push inward with the foot into the object to contract the muscles within the ankle. Hold the contraction for 10 seconds.
Alternatively, push the ankle down or up against a fixed object to strengthen and improve mobility. Once isometric exercises have been mastered, progress to isotonic exercises, which are performed with a resistance band, recommends the AOFAS. For example, place the band around the forefoot, and hold the ends with your hands. Gently push the ankle down as far as possible, and return to the starting position.
Three exercises suggested by the AOFAS involve tying the band around a fixed object and then attaching it to the foot. The first is to wrap the ends around the forefoot and begin with the foot pointing down, then pull the ankle up as far as possible. The second is to wrap the band around the outer side of the ankle and begin with the foot relaxed, then move the ankle down and in. The third exercise is to wrap the band around the inside of the ankle and relax the foot, then move the foot up and out.