Effect of electrical stimulation on human skeletal muscle

The acute and adaptive effects of electrical stimulation of the quadriceps muscle were investigated in healthy male volunteers. The acute effects, i.e., depletion of phosphagen and glycogen stores and formation of lactate as well as decreases in certain enzyme activities, were similar to those found earlier for intense muscular exercise. Intermittent electrical stimulation for 4 to 5 weeks did not cause any significant changes in enzyme activities, muscle fiber characteristics, or mitochondrial properties. A 4-week period of electrical stimulation resulted in improvements of muscle strength comparable to the results of a corresponding program of voluntary training. However, the effects of electrical stimulation appeared more "position-specific" and less "speed-specific" than those of voluntary training with slow isokinetic contractions.