Effects of prior heavy-intensity exercise on oxygen uptake and muscle deoxygenation kinetics of a subsequent heavy-intensity cycling and kneeextension exercise

This study examined the effects of prior heavy-intensity exercise on the adjustment of pulmonary oxygen uptake (VO _2p) and muscle deoxygenation Δ[HHb] during the transition to subsequent heavy-intensity cycling (CE) or knee-extension (KE) exercise. Nine young adults (aged 24 ± 5 years) performed 4 repetitions of repeated bouts of heavy-intensity exercise separated by light-intensity CE and KE, which included 6 min of baseline exercise, a 6-min step of heavy-intensity exercise (H1), 6-min recovery, and a 6-min step of heavy-intensity exercise (H2). Exercise was performed at 50 r·min ^-1 or contractions per minute per leg. Oxygen uptake (VO ₂) mean response time was ~20% faster (p < 0.05) during H2 compared with H1 in both modalities. Phase 2 time constants (τ) were not different between heavy bouts of CE (H1, 29.6 ± 6.5 s; H2, 28.0 ± 4.6 s) or KE exercise (H1, 31.6 ± 6.7 s; H2, 29.8 ± 5.6 s). The VO ₂ slow component amplitude was lower (p < 0.05) in H2 in both modalities (CE, 0.19 ± 0.06 L·min ^-1; KE, 0.12 ± 0.07 L·min ^-1) compared with H1 (CE, 0.29 ± 0.09 L·min ^-1; KE, 0.18 ± 0.07 L·min ^-1), with the contribution of the slow component to the total VO ₂ response reduced (p < 0.05) in H2 during both exercise modes. The effective tHHb was similar between bouts for CE (H1, 18.2 ± 3.0 s; H2, 18.0 ± 3.6 s) and KE exercise (H1, 26.0 ± 7.0 s; H2, 24.0 ± 5.8 s). The DHHb slow component was reduced during H2 in both CE and KE (p < 0.05). In conclusion, phase 2 VO _2p was unchanged with priming exercise; however, a faster mean response time of VO _2p during the heavy-intensity exercise preceded by a priming heavy-intensity exercise was attributed to a smaller slow component and reduced muscle deoxygenation indicative of improved muscle O ₂ delivery during the second bout of exercise.