Prolonged moderate-intensity exercise oxygen uptake response following heavy-intensity priming exercise with short- and longer-term recovery

This study examines the effects of recovery duration following heavy-intensity "priming" exercise (Hvy) on pulmonary oxygen (O₂) uptake (V̇O_2p) during subsequent prolonged moderate-intensity exercise (Mod). Nine participants (6 men and 3 women) (27 ± 7 years) each completed 3 repetitions of 2 continuous Mod 1-Hvy-Mod 2 leg-cycling protocols in which Mod 2 lasted 30 min, but was preceded by a recovery duration of either 6 (R₆) or 20 (R₂₀) min at 20 W following Hvy; in each case, Mod 1 and Hvy lasted 6 min and were preceded by 6 min at 20 W. V̇O_2p, heart rate (HR), and near-infrared spectroscopy (NIRS)-derived muscle deoxygenation ([HHb]) responses were modeled as a monoexponential; additionally, 60-s averages were computed every 6 min in Mod 1 and Mod 2. V̇O_2p was elevated (p < 0.05) throughout Mod 2 compared with Mod 1 in both R₆ and R₂₀ (by -82 mL·min-1 or ~5.0%); this occurred despite a complete recovery of baseline V̇O_2p (V̇O_2pBsln) following R₂₀. HR and minute ventilation (V̇E), but not [HHb], were also elevated throughout Mod 2. The phase II time constant forV̇O_2p (τV̇O_2p) was reduced in Mod 2 (22 s (Mod 1), 19 s (Mod 2); p < 0.05), as was the "overshoot" in the normalized [HHb]/O₂ uptake ratio (p < 0.05). This study shows that V̇O_2p was elevated during Mod following Hvy, regardless of recovery duration; however, a determining role for V̇O_2pBsln is precluded. Furthermore, neitherV̇O_2p, HR, norV̇E showed any evidence of a readjustment back to no-Hvy conditions during prolonged Mod (p > 0.05). Lastly, regardless of recovery duration, τV̇O_2p was reduced to a similar extent with Hvy, likely resulting from an improved matching of local muscle O₂ delivery to O₂ utilization.