The efficiency of electrical stimulation on muscle groups of different size

Abstract

Although a vast quantity of literature is available at the present time involving the use of electrical muscle stimulation (EMS) for the purpose of training human skeletal muscles there is no clear agreement on the efficiency of this procedure. The present study has investigated specific variables of EMS application in an attempt to clarify the efficiency of EMS and to then predict the results of prolonged training. Ten healthy male volunteers participated in the study. EMS was applied to both the quadriceps muscle group and the calf muscle group. Two different size electrodes were used on each muscle group. The stimulating unit was an Electrostim 180 which produces a sine wave at a frequency of 50Hz. Each subject performed two maximal voluntary contractions (MVC) for the particular muscle group. Unassisted contractions produced by the EMS were then elicited with different size electrodes. The testing apparatus was a dual channel Cybex II dynamometer. Increasing the intensity of stimulation beyond a certain level did not cause an increase in force output. The results demonstrate that EMS produces inferior force output in comparison to MVC. Electrical stimulation of the quadriceps muscle group was found to be more efficient than in the calf muscle group. The smaller sized electrodes (6¼ X 6¼ cm) were also found to be more efficient in stimulation of both muscle groups in comparison with the larger electrodes (12½ X 7½ cm). It was concluded that although EMS is less efficient than MVC in producing force output in a muscle group, it does meet minimal requirements for anticipated strength gains with prolonged training. It was also concluded that electrode size plays a significant role in the efficiency of stimulation.