William E Hughes, Nicholas T Kruse, Kenichi Ueda, Darren P Casey

We tested the hypothesis that aging is associated with prolonged leg vasodilator kinetics and habitual exercise training in older adults improves these responses relative to untrained older adults. Additionally, we examined the relationship between contraction-induced rapid onset vasodilation (ROV) and vasodilator kinetics. Young (n=10), older untrained (n=13) and older trained (n=14) adults performed single and rhythmic knee-extension contractions at 20% and 40% work-rate maximum (WRmax). Femoral artery diameter and mean blood velocity were measured by Doppler ultrasound. Vascular conductance (VC; ml·min-1·mmHg-1) was calculated using blood flow (ml·min-1) and mean arterial pressure (mmHg). The primary outcome was the kinetic response (mean response time; MRT), modeled using an exponential model, expressed as the number of duty cycles to change 63% of the steady-state amplitude. There was no age or training related differences in VC MRT between the groups at 20% WRmax. Older untrained adults exhibited prolonged VC MRT at 40% WRmax relative to young (37{plus minus}16 vs. 24{plus minus}10 duty-cycles; P<0.05) and older trained adults (37{plus minus}16 vs. 23{plus minus}14 duty-cycles; P<0.05). There were no differences in VC MRT between young and older trained adults at 40% WRmax (P=0.96). There were no associations between peak ROV and VC MRT at 20% or 40% WRmax (r=-0.08 and 0.22; P=0.67 and 0.20, respectively) in the group as a whole. Our data suggest 1) advancing age prolongs leg vasodilator kinetics; 2) habitual exercise training in older adults offsets this age-related prolongation; and 3) contraction-induced ROV is not related to vasodilator kinetics within a group of young and older adults.