Effect of moderate-intensity work rate increment on phase II τVO2, functional gain and Δ[HHb]

This study systematically examined the role of work rate (WR) increment on the kinetics of pulmonary oxygen uptake (VO2p) and near-infrared spectroscopy (NIRS)-derived muscle deoxygenation (Δ[HHb]) during moderate-intensity (Mod) cycling. Fourteen males (24 ± 5 years) each completed four to eight repetitions of Mod transitions from 20 to 50, 70, 90, 110 and 130 W. VO2p and Δ[HHb] responses were modelled as a mono-exponential; responses were then scaled to a relative % of the respective response (0–100 %). The Δ[HHb]/VO2 ratio was calculated as the average Δ[HHb]/VO2 during the 20–120 s period of the on-transient. When considered as a single group, neither the phase II VO2p time constant (τVO2p; 27 ± 9, 26 ± 11, 25 ± 10, 27 ± 14, 29 ± 13 s for 50–130 W transitions, respectively) nor the Δ[HHb]/VO2 ratio (1.04 ± 0.13, 1.10 ± 0.13, 1.08 ± 0.07, 1.09 ± 0.11, 1.09 ± 0.09, respectively) was affected by WR (p > 0.05); yet, the VO2 functional gain (G; ΔVO2/ΔWR) increased with increasing WR transitions (8.6 ± 1.3, 9.1 ± 1.2, 9.5 ± 1.0, 9.5 ± 1.0, 9.9 ± 1.0 mL min−1 W−1; p 0.05). The Δ[HHb]/VO2 ratio was smaller (p