Effect of electrical stimulation of leg muscles on physiological responses during arm-cranking exercise in healthy men

The purpose of this study was to investigate the hypothesis that changes in physiological responses during arm-cranking exercise using electrical stimulation of the leg muscles (ACE-ES) compared to arm-cranking exercise alone (ACE) in able-bodied subjects (ABS) are based on an increase in active muscle mass rather than the enhancing effect of the leg muscle pump. In ABS the sympathetic nervous system induced vasoconstriction and activity of the leg muscle pump are intact, therefore, a normal redistribution of blood takes place during exercise. Consequently, ES should have no additional effect on the redistribution of blood in these ABS during exercise and, thus, changes in physiological responses will be based on an increase in active muscle mass. A group of 11 ABS performed three maximal arm-cranking tests. In the first test peak power output (POpeak) was determined. The other tests were both submaximal and maximal ACE, once with ACE-ES and once with ACE. The POpeak was not significantly different between ACE-ES and ACE. Oxygen uptake (VO2) increased significantly during ACE-ES compared to ACE. Cardiac output (Q(c)), stroke volume (SV), heart rate and ventilation were not significantly different during ACE-ES compared to ACE. Respiratory exchange ratios were significantly lower during ACE-ES compared to ACE at 60% POpeak and at maximal exercise. In conclusion, ACE-ES caused significant increases in VO2 with a lack of elevation in Q(c) and SV during submaximal and maximal exercise in ABS. The results of this study suggest that changes in physiological responses during ACE-ES are based on an increase in the active muscle mass rather than stimulation of the leg muscle pump.