1. Four paraplegic men volunteered for an exercise programme in which their paralysed quadriceps muscles were stimulated by means of computer-regulated electrical impulses applied through external electrodes. The first exercise regimen consisted of leg raising against a graded load, and during the second regimen exercise took the form of cycling on a modified bicycle ergometer. Each subject exercised five times weekly for 10 weeks during the first regimen and 32 weeks during the second regimen.
2. Whole-body protein turnover determined by l-[1-13C]leucine during feeding remained constant during both exercise regimens, when expressed either in terms of body weight or fat-free mass derived from measurements of total body potassium.
3. Quadriceps muscle protein synthetic rate increased during the study, from 0.0712 to 0.0985%/h (P < 0.05), as did quadriceps muscle area assessed by computed tomography.
4. Bone mineral content for lumbar vertebrae was normal in all four patients, but for the femoral mid-shaft bone mineral content averaged only 66% of normal for three of the patients. Trabecular bone density in the distal tibia ranged from normal to 2% of normal for the men with the shortest and longest periods of disability, respectively. No changes in bone mineral content or bone density occurred during the exercise period.