A serious ankle injury often require athletes to keep their ankles immobilized for extended periods of time, and these periods of immobilization can drastically weaken ankle muscles and connective tissues. Is there any way to prevent at least some of this loss of strength?
Based on past research, sports medicine specialists have theorized that strenuous training of the non-injured ankle might produce a 'cross-over' effect, i. e., the injured ankle, even though it does not engage in actual exercise, might somehow benefit from the opposite-ankle's training and maintain its general strength. While that might seem far-fetched, 'one-leg' studies in which only one leg is exercised during training have documented increases in strength in the non-trained leg. Might not the same be true for injured ankles?
To begin to look into that possibility, researchers recently carried out a randomized, controlled, clinical trial with 20 individuals who had no history of ankle injuries ('The benefit of a single-leg strength training program for the muscles around the untrained ankle,' Am J Sports Med, vol. 28 (4), pp. 568-573, 2000). The subjects were randomly divided into two groups: control (CON) and training (TR). Both groups underwent isokinetic testing of the ankle muscles at the beginning and end of an eight-week training period, which required TR subjects to work out three times per week.
Control-group members simply maintained normal activities between the tests. An extremely interesting aspect of this study was that half of the TR subjects trained only their dominant (i. e., preferred, stronger) ankles while the other half trained only their non-dominant ankles during the eight-week period. Inclusion of dominant and non-dominant training was important. One might reasonably argue, for example, that cross-overs in strength might take place differently from dominant to non-dominant ankle, versus from non-dominant to dominant. Not much is known about this, but it's possible that strength gains in the non-dominant leg would be greater than those in the dominant leg as a result of systematic training - and therefore that there would be greater strength to 'carry over' to the other appendage.
Not surprisingly, CON-group members failed to improve peak torque, power, or endurance during the eight-week period. In the TR sub-groups, subjects who trained the dominant leg only improved peak torque values by 8.5% in the trained ankle and by 1.5% in the untrained ankle. Subjects who trained the non-dominant leg only improved peak torque values by 9.3% in the trained leg and 3.5% in the untrained leg, suggesting that there might be greater cross-over from non-dominant to dominant.
Those were the averages; in some cases the gains were considerably greater. For example, training the ankle muscles resulted in an improvement in peak torque as high as 40% in the trained leg and a cross-over benefit as great as 19% in the untrained leg!
Bear in mind that TR-group members' did not have one ankle immobilized, as would be the case for athletes with serious ankle injuries. We'll wait to see whether that makes a difference in the cross-over of strength; one might argue that cross-over would be greater to an immobilized body part, since mobilized areas of the body are already getting some training of their own during normal activity and thus would be less likely to be impacted by cross-overs. Conversely, you could contend that if normal movement is lost, the affected body part will be so weak and uncoordinated once movement resumes that it will be impossible for cross-over alone to upgrade strength.
As the investigators logically concluded, 'This ... strength training technique deserves further investigation in an injured population where the benefits during rehabilitation may be more substantial.' The research suggests that it is indeed possible that strenuous training of an uninjured limb might help preserve strength in an immobilized limb; this would of course help the injured limb come back to full strength more quickly once mobility is regained.
What's the mechanism for all this? Remember that your nervous system is clever. Once it learns how to coordinate stronger movements in one part of your body, it can utilize that pattern of control with other, similar body parts and make those regions stronger, even though they have not engaged in a single second of exercise.