Sympathetic nervous system activation reduces contraction-induced rapid vasodilation in the leg of humans independent of age

Contraction-induced rapid vasodilation is attenuated similarly in the upper and lower limbs of older adults. In the forearm, this attenuation is in part due to a greater sympathetic vasoconstriction. We examined whether the age-related reduction in contraction-induced vasodilation in the leg is also due to a sympathetic vasoconstrictive mechanism. Thirteen young (24 ± 1 yr) and twelve older adults (67 ± 1 yr) performed single-leg knee extension at 20 and 40% of work-rate maximum (WR max ) during control and cold-pressor test (CPT) conditions. Femoral artery diameter and blood velocity were measured using Doppler ultrasound. Vascular conductance (VC; ml·min −1 ·mmHg −1 ) was calculated using blood flow (ml/min) and mean arterial pressure (mmHg). Peak (ΔVC from baseline) and total VC were blunted in older adults during control conditions across exercise intensities ( P < 0.05). Peak and total VC were reduced during CPT in both age groups across exercise intensities ( P < 0.05). The relative change (i.e., %reduction; CPT vs. control) in peak (−25 ± 5 vs. −22 ± 4% at 20% WR max ; and −21 ± 6 vs. −27 ± 5% at 40% WR max ; P = 0.42–0.55) and total VC (−28 ± 5 vs. −36 ± 6% at 20% WR max ; and −22 ± 8 vs. −33 ± 5% at 40% WR max ; P = 0.23–0.34) were similar between young and older adults. When matched for absolute workload (~10 W), age differences persisted in peak VC ( P < 0.05) under both conditions, with similar relative changes in peak and total VC during CPT. Our data suggest that 1) sympathetic stimulation reduces contraction-induced rapid vasodilation in the leg of young and older adults similarly; and 2) enhanced sympathetic vasoconstriction does not fully explain age-related differences in contraction-induced vasodilation within the leg. NEW & NOTEWORTHY Aging is associated with attenuated contraction-induced rapid onset vasodilation (ROV). Within the forearm, this attenuation is partially due to enhanced sympathetic vasoconstriction. In the current study, we found that sympathetic vasoconstriction reduces contraction-induced ROV within the leg of both young and older adults, with the magnitude of change being similar between age groups. Our current results suggest that age-related attenuations in contraction-induced ROV within the leg are not fully explained by a sympathetic vasoconstrictor mechanism.