Four weeks of cycle training increases basal production of nitric oxide from the forearm

The purpose of this study was to determine whether nontrained vascular beds might contribute to the beneficial effects of exercise, including reduced blood pressure by enhanced nitric oxide production. Thirteen healthy, sedentary male volunteers performed 4 wk of normal sedentary activity and 4 wk of cycle training in a randomized order. At the end of each intervention, venous occlusion plethysmography was used to study the forearm blood flow responses to intra-arterial infusions of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA), acetylcholine, and sodium nitroprusside. Training increased the maximal work-load and maximal oxygen consumption, whereas intrabrachial blood pressure was reduced. L-NMMA caused a greater vasoconstriction after training (P = 0.004). Net nitrate and nitrite consumption by the forearm was less after training both before and after administration of L-NMMA (P = 0.04), consistent with increased nitrate and nitrite production from nitric oxide metabolism. There was no difference in the response to acetylcholine or sodium nitroprusside between the two states. Preliminary studies showed an increase in forearm blood flow and blood viscosity after cycling, suggesting that elevated shear stress in this vascular bed may contribute to endothelial adaptation and the cardiovascular protective effects of exercise training.