1. Six patients were studied after prolonged immobilization of an injured leg resulting in muscle atrophy.
2. The forces exerted by the atrophied and normal legs during continuous dynamic exercise (one- and two-leg cycling) were examined by a specially adapted ergometer.
3. In one-leg cycling the peak force exerted on the crank at a given work rate, the net work rate performed on the crank, and the proportion of work rate performed in leg extension and flexion phases of the cycle were the same whether the atrophied or normal limb was used.
4. Despite these similarities there was an unexplained reduction in efficiency when using the atrophied leg to perform one-leg cycling.
5. In two-leg cycling the peak force exerted at a given work rate by the atrophied leg was reduced by about 40% as compared with the normal leg, which reflected a similar reduction in the contribution of that leg to the total net work rate. Possible reasons and implications for this disproportionate sharing of work between the normal and atrophied leg are discussed.