Effects of priming exercise on the speed of adjustment of muscleoxidative metabolism at the onset of moderate-intensity steptransitions in older adults.

Ageing is associated with a functional decline of the oxidative metabolism due to progressive limitations of both O(2) delivery and utilization. Priming exercise (PE) increases the speed of adjustment of oxidative metabolism during successive moderate intensity transitions. We tested the hypothesis that such improvement is due to a better matching of O(2) delivery to utilization within the working muscles. In 21 healthy older adults (65.7± 5 yrs) we measured contemporarily and non-invasively indexes of the overall speed of adjustment of the oxidative metabolism (i.e. pulmonary V O(2) kinetics), of the bulk O(2) delivery (i.e. cardiac output) and of the rate of muscle deoxygenation (i.e. deoxygenated haemoglobin, HHb) during moderate intensity step transitions, either with (ModB) or without (ModA) prior PE. The local matching of O2 delivery to utilization was evaluated by the ΔHHb/Δ V O(2) ratio index. The overall speed of adjustment of the V O(2) kinetics was significantly increased in ModB compared to ModA (p<0.05). On the contrary, the kinetics of cardiac output was unaffected by PE. At the muscle level, ModB was associated with a significant reduction of the "overshoot" in the ΔHHb/Δ VO(2) ratio compared to ModA (p<0.05), suggesting an improved O(2) delivery. Our data are compatible with the hypothesis that, in older adults, PE, prior to moderate intensity exercise, beneficially affects the speed of adjustment of oxidative metabolism due to an acute improvement of the local matching of O(2) delivery to utilization.