Strengthening of human quadriceps muscles by cutaneous electrical stimulation

Abstract

The effectiveness of cutaneous electrical stimulation as a muscle-strengthening technique was evaluated by comparison with an isometric regime. Sixteen normal healthy subjects were randomly assigned to either an electrical group or an isometric group. A pretest was given of maximum voluntary force in the quadriceps (extensor) muscles, measured with a cable tensiometer. Subjects then trained (isometrically or by electrical stimulation) four days per week for three weeks. Training by electrical stimulation was via a square-wave pulse (75 Hz and 0.1 ms) with the voltage determined by subject tolerance for ten, 10-sec induced contractions (with 50-sec rest intervals). Isometric training consisted of ten, 10-sec maximal contractions (with 50-sec rest intervals) at each session. Feedback of the generated force was standardised for both groups. Post-training measures were then administered using the same protocol as the pretest. Both groups demonstrated a marked improvement in quadriceps strength of 22 +/- 5.3% for the electrical group and 25 +/- 6.9% increase for the isometric group (p less than 0.02). The change in strength was apparently not dependent on the magnitude of the stimulating voltage (5-10 V) nor on the tension induced. There was no significant difference in the strength gains achieved by the two regimes (p greater than 0.05). No pain, muscle lesions or other ill effects were observed with electrical stimulation. We conclude that cutaneous electrical stimulation is a viable strengthening technique. There are obvious practical applications of this technique to the rehabilitation of patients who are not able to maintain an effective voluntary contraction.