Improvement in Knee Extension Strength through Training by Means of Combined Electrical Stimulation and Voluntary Muscle Contraction

Weight training (WT) is the most common method of maintaining and increasing muscle strength. WT, however, is not always useful as it requires the external resistance and stabilization. We have developed a “hybrid training” (HYB) approach that avoids these problems by using electrically stimulated muscles to provide resistance to the motion of a muscle undergoing training. Here we report the efficacy of HYB compared with conventional WT for increasing the muscle strength around the knee at both slow and fast joint speeds (at 30 and 180°/sec). Two matched groups, each of 8 healthy men aged 22 years, exercised 3 times/week for six weeks. Both groups showed significantly increased strength in concentric torque at 30°/sec (HYB +28%, WT +33%) and at 180°/sec (HYB +33%, WT +38%), and also in eccentric torque at 30°/sec (HYB +25%, WT +24%) and at 180°/sec (HYB +19%, WT +30%) (p < 0.001). HYB is comparable with WT exercising with the exception of high-speed contractions, while HYB has a clear advantage in not needing external resistance equipment or stabilization. HYB is therefore considered a useful approach for strengthening muscles when a person is restricted to bed rest or during space flight.