Effect of unilateral forearm inactivity on endothelium-dependent vasodilator function in humans

Exercise training is associated with rapid changes in endothelium-dependent vasodilation, which occur within days of training. Whilst long-term physical inactivity has potent effects on vascular structure, little is known about the immediate impact of inactivity on vascular function. Aim of this study was to measure vascular function before, during (day 4) and after 8 days of unilateral forearm inactivity. Thirteen healthy male subjects (22 ± 1 years) were instructed to wear a sling on the non-dominant arm to induce local inactivity. Before, during (at 4 days) and after the 8-day intervention, we used echo Doppler to measure bilateral brachial artery dilator response to 5-min ischaemia [i.e. flow-mediated dilation (FMD)], ischaemic handgrip exercise (iEX) and endothelium-independent dilation to a NO donor [i.e. glyceryl trinitrate (GTN)]. Maximal handgrip strength of the inactive forearm significantly decreased after 8 days (t tests P = 0.03 for Day 0 vs. Day 8), confirming physical deconditioning in the inactive forearm. A significant decrease in peak blood flow was found in the intervention arm (sling: 539 ± 236, 528 ± 184, 384 ± 142 ml/min) relative to the control arm (559 ± 181, 591 ± 219, 613 ± 169 ml/min; 2-way ANOVA interaction: P = 0.05). Analysis revealed no significant change in brachial artery baseline diameter, FMD %, iEX or GTN across the 8 days in either arm (P > 0.05). Eight days of forearm physical inactivity induced a significant decrease in post-ischaemic limb blood flow, suggestive of remodelling of forearm resistance vessels. However, measures of conduit artery endothelium-dependent vasodilation were not altered across an 8-day period of inactivity, suggesting that initial remodelling occurs at distal ends of the vascular tree.