Effect of heavy-intensity 'priming' exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity step-transitions initiated from an elevated work rate

We examined the effect of heavy-intensity 'priming' exercise on the rate of adjustment of pulmonary O2 uptake (τV˙O2p) initiated from elevated intensities. Fourteen men (separated into two groups: τV˙O2p ≤ 25s [Fast] or τV˙O2p > 25s [Slow]) completed step-transitions from 20 W to 45% lactate threshold (LT; lower-step, LS) and 45% to 90%LT (upper-step, US) performed (i) without; and (ii) with US preceded by heavy-intensity exercise (HUS). Breath-by-breath V˙O2p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb + Mb]) were measured. Compared to LS, τV˙O2p was greater (p < 0.05) in US in both Fast (LS, 19 ± 4s; US, 30 ± 4s) and Slow (LS, 25 ± 5s; US, 40 ± 11s) with τV˙O2p in US being lower (p < 0.05) in Fast. In HUS, τV˙O2p in Slow was reduced (28 ± 8s, p < 0.05) and was not different (p > 0.05) from LS or Fast group US. In Slow, τ[HHb + Mb] increased (p < 0.05) in US relative to HUS; this finding coupled with a reduced τV˙O2p indicates a priming-induced improvement in matching of muscle O2 delivery-to-O2 utilization during transitions from elevated intensities in those with Slow but not Fast V˙O2p kinetics.