Adaptation of pulmonary O2 uptake kinetics and muscle deoxygenation at the onset of heavy-intensity exercise in young and older adults.

The purpose was to examine the adaptation of pulmonary O₂ uptake (V_O2p)and deoxygenation of the vastus lateralis muscle at the onset of heavy-intensity, constant-load cycling exercise in young (Y; 24 ± 4 yr; mean ± SD; n = 5) and older (O; 68 ± 3 yr; n = 6) adults. Subjects performed repeated transitions on 4 separate days from 20 W to a work rate corresponding to heavy-intensity exercise. V_O2p was measured breath by breath. The concentration changes in oxyhemoglobin, deoxyhemoglobin (HHb), and total hemoglobin/myoglobin were determined by near-infrared spectroscopy (Hamamatsu NIRO-300). V_O2p data were filtered, interpolated to 1 s, and averaged to 5-s bins. HHb-near-infrared spectroscopy data were filtered and averaged to 5-s bins. A monoexponential model was used to fit V_O2p [phase 2, time constant (τ) of V_O2p] and HHb [following the time delay (TD) from exercise onset to the start of an increase in HHb] data. The τV_O^2p was slower (P < 0.001) in O (49 ± 8 s) than Y (29 ± 4 s). The HHb TD was similar in O (8 ± 3 s) and Y (7 ± 1 s); however, the τ HHb following TD was faster (P < 0.05) in O (8 ± 2 s) than Y (14 ± 2 s). The slower V_O2p kinetics and faster muscle deoxygenation in O compared with Y during heavy-intensity exercise imply that the kinetics of muscle perfusion are slowed relatively more than those of V_O2p in O. This suggests that the slowed V_O2p kinetics in O may be a consequence of a slower adaptation of local muscle blood flow relative to that in Y. [ABSTRACT FROM AUTHOR]