Influence of electrical stimulation on dynamic forces of the arm flexors in strength-trained and untrained men

Abstract

We examined the influence of activation and strength-training history on the force-velocity relationship. Over 4 days, maximal isometric (MVC) and concentric and eccentric constant angle isokinetic forces at 6 velocities were measured in the arm flexors of 6 strength-trained men and 6 untrained men under voluntary condition and with electromyostimulation (EMS) (2.5 kHz sine wave, 50 burst · s−1, 50% duty cycle) superimposed on the voluntary muscle actions. Trained men were 31% stronger than untrained controls. Voluntary concentric forces decreased with increasing velocities and were less than MVC in both groups. Voluntary eccentric forces exceeded MVC only in the trained men. Untrained men tolerated 21.9 mA and trained men 31.3 mA of EMS current, yet tetanic forces were similar: 92.5 N versus 96.0 N. These data suggest that, independent of training status, percutaneous EMS inhibits voluntary forces of the arm flexors. Modifications of the EMS parameters may be necessary to allow for the more complete study of the influence of training history on muscle mechanics and the neural regulation of force production.