Responses of muscle sympathetic nerve activity to static biceps brachii contraction in humans.

The aim of the present study was to determine whether static biceps brachii contraction by handcurling enhances the muscle sympathetic nerve activity (MSNA) in the resting muscle. In six healthy men (age: 19-23 years), we measured MSNA in the tibial nerve microneurographically, with heart rate, blood pressure, biceps electromyogram (EMG), and the intensity of local fatigue sensation in the working muscle. Subjects performed static biceps brachii contraction for 2 min (short exercise) at 30% of maximal voluntary contraction, and then they made fatiguing exercise to exhaustion (long exercise). During the short exercise, the heart rate and mean arterial blood pressure increased significantly (p < 0.05). In the last 30s of the short exercise, the MSNA burst rate and total MSNA increased significantly but integrated EMG did not increase. In long exercise, MSNA burst rate, total MSNA, mean arterial blood pressure, heart rate, EMG activity, and local fatigue sensation increased progressively with advancing exercising time. There was a significant correlation between integrated EMG and total MSNA (r = 0.64, n = 63, p < 0.001), and local fatigue sensation and total MSNA (r = 0.41, n = 63, p < 0.001) during the long exercise. Post-exercise recovery of the MSNA response to static handcurling was more prompt in short exercise than that in long exercise. We conclude that MSNA is enhanced during submaximal static handcurling, and the magnitude of enhancement correlates with EMG activity and subjective fatigue sensation in the biceps brachii, which might be attributed to the stimulation of metaboreceptors in the working muscle.