Circulatory responses to voluntary and electrically induced muscle contractions in humans

Background and Purpose: Transcutaneous electrical nerve stimulation (TENS) increases regional blood flow when applied at intensities sufficient to cau se skeletal muscle contraction. It is not known whether increases in blood flow elicited by TENS differ from those caused by voluntary muscle contract ion. The purpose of this study, therefore, was to compare the hemodynamic e ffects of these 2 tripes of muscle contraction. Subjects and Methods. Fourt een people with no known pathology, aged 18 to 49 years ((X) over bar=28, S D=8), sewed as subjects. Calf blood flow (venous occlusion plethysmography) , heart rate (electrocardiogram), blood pressure (automated sphygmomanometr y), and force (footplate transducer) were measured during electrically indu ced and voluntary contractions. Results. Both modes of exercise caused rapi d, but short-lived vasodilation (calf vascular resistance [(X) over bar+/-S EM]: -53%+/-3% for voluntary contractions versus -57%+/-4% for electrically induced contractions). The vasodilation caused by electrically induced con tractions persisted for at least 15 seconds in the postexercise period, whe reas the vasodilation elicited by voluntary contractions had resolved by th is time point. Conclusion and Discussion. The hemodynamic changes elicited by voluntary and electrically induced muscle contractions are similar in ma gnitude but different in duration.