Isokinetic strength training in below-knee amputees.
Eight below-knee amputees performed isokinetic training of knee extensor- and knee-flexor muscles for a period of 8-12 weeks at angular velocities of 60 degrees/s, 180 degrees/s and 240 degrees/s. Before and after training isokinetic and isometric knee extensor/flexor strength was measured. Muscle biopsies were taken from the vastus lateralis and the cross-sectional area of the thigh muscles was measured with computerized tomography. Peak torque of the amputated leg increased significantly in all knee-extension tests and in knee-flexion at 180 degrees/s, and in the non-amputated leg in extension at 180 degrees/s, 240 degrees/s and for isometric strength at 60 degrees knee angle. Knee-flexion strength increased at 240 degrees/s. The cross-sectional area of the muscle fibers increased in the amputated leg in all patients except one. There was no significant increase in the non-amputated leg which also was trained. The quotient between the cross-sectional areas of type II and type I fibers increased from 1.04 to 1.20 in the amputated leg, demonstrating an increase specially in the type II fibers. There was no difference in the non-amputated leg. The cross-sectional area of the thigh muscles did not show any significant change in either leg. The patients estimated their ability to walk after training to more than double the distance compared to before training. They could also manage better without walking aids. The increase in strength and the synchronous increase in the size of type II (fast twitch) fibers indicate that the training model has activated also these motor units which probably have not been given as much training earlier.