Similar pattern of change in V̇o2 kinetics, vascular function, and tissue oxygen provision following an endurance training stimulus in older and young adults

Abstract

<p class="first" id="d12269981e222">The purpose of this study was to examine the time course of changes in the oxygen uptake (V̇ <span style="font-variant: small-caps">o</span> ₂) kinetics response subsequent to short-term exercise training (i.e., 24, 48, 72, and 120 h posttraining) and examine the relationship with the time course of changes in microvascular [deoxygenated hemoglobin concentration ([HHb])-to-V̇ <span style="font-variant: small-caps">o</span> ₂ ratio ([HHb])/V̇ <span style="font-variant: small-caps">o</span> ₂)] and macrovascular [flow-mediated dilation (FMD)] O ₂ delivery to the active tissues/limbs. Seven healthy older [OA; 74 ± 6 (SD) yr] and young men (YA; 25 ± 3 yr) completed three endurance cycling exercise training sessions at 70% V̇ <span style="font-variant: small-caps">o</span> _2peak. Moderate-intensity exercise on-transient V̇ <span style="font-variant: small-caps">o</span> ₂ (measured breath by breath) and [HHb] (measured by near-infrared spectroscopy) were modeled with a monoexponential and normalized (0–100% of response), and the [HHb])/V̇ <span style="font-variant: small-caps">o</span> ₂was calculated. Ultrasound-derived FMD of the popliteal artery was assessed after 5 min of cuff occlusion. %FMD was calculated as the greatest percent change in diameter from baseline. Time constant of V̇ <span style="font-variant: small-caps">o</span> ₂ (τV̇ <span style="font-variant: small-caps">o</span> ₂) was significantly reduced in both OA (~18%) and YA (~23%) at 24 h ( <i>P</i> &lt; 0.001) posttraining and remained decreased at 48 h before returning toward pretraining (PRE) values. Both groups showed a significant decrease in the [HHb])/V̇ <span style="font-variant: small-caps">o</span> ₂ at 24, 48, and 72 h ( <i>P</i> = 0.001, 0.01, and 0.03, respectively) posttraining before returning toward PRE values at 120 h. %FMD followed a similar time course to that of changes in the [HHb])/V̇ <span style="font-variant: small-caps">o</span> ₂, being significantly greater in both OA (by ~64%) and YA (by ~26%) at 24 h ( <i>P</i> &lt; 0.001), remaining increased at 48 and 72 h ( <i>P</i> = 0.02 and 0.03, respectively), and returning toward PRE values at 120 h. These data suggest the rate of adjustment of V̇ <span style="font-variant: small-caps">o</span> ₂ may be constrained by O ₂ availability in the active tissues. </p>