Voluntary and electromyostimulation forces in trained and untrained men

Abstract

Electromyostimulation (EMS) evoked responses of lower extremity muscles of sedentary or disabled subjects have been extensively studied to improve muscular strength and delay atrophy. However, it is not apparent whether EMS can serve a similar function in upper extremity muscles and in athletes. We compared the forces of maximal voluntary isometric contraction (MVC), percutaneous EMS-evoked tetanus, and EMS superimposed on MVC of the elbow flexors in six strength-trained and six untrained healthy men. Stimulation consisted of a 2.5-kHz alternating current sine wave modulated at 50 bursts.s-1 with a 50% duty cycle. Reliability of the criterion measures was assessed over 4 d and ranged from R = 0.746 to R = 0.948. Strength-trained men had 29% higher MVC than untrained controls (P less than 0.001). Untrained men tolerated 21.9 mA and trained men 31.3 mA of EMS current (P less than 0.021), yet tetanic forces were similar: 92.5 N vs 96.0 N (P greater than 0.196). These tetanic forces corresponded to 32% (untrained) and 24% (trained) of MVC (P less than 0.047). When EMS was superimposed on MVC, compared with MVC alone, force was significantly (P less than 0.048) lower by 10% (31 N, untrained) and 13% (55 N, trained). These data suggest that, independent of training status, percutaneous EMS reduces maximal voluntary elbow flexion forces and that tetanic forces may not be sufficiently high for purposes of muscular strength development or prevention of atrophy.