Blood flow in the resting forearm during prolonged contralateral isometric handgrip at maximal effort

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Abstract
Muscle contraction performed as handgrip at constant force, at 1/3 of maximal voluntary contraction (MVC), induced a rapid vasodilation in the resting contralateral forearm which may be neurogenically mediated, followed by a relative increase in resistance. Maintenance of contraction at 1/3 MVC for 2 min requires continuously increasing effort because of fatigue, as evidenced by emg [electromyography]. The biphasic response of the vascular bed may then be related to the increasing intensity of somatomotor activation which is needed to maintain contraction force, or, alternatively, to differences in vasomotor activity on initiation of and continued muscle activity. Blood flow in the resting forearm was measured during contralateral handgrips at constant maximal effort for 6 min (in which case force will drop) and compared to handgrip at constant force at 1/3 MVC for 2 min. The flow reaction during prolonged contraction at maximal effort was similar to that induced by contraction at constant force with a marked transient lowering of vascular resistance, although maximal vasodilation was more pronounced and occurred earlier. The rapid decrease in vascular resistance was related primarily to initiation of somatomotor activity, whereas continued muscle contraction produced a relative increase in vasoconstrictor activity irrespective of changes in contraction effort.