Influence of priming exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity cycling in type 2 diabetes

The pulmonary oxygen uptake (V̇O2) kinetics during the transition to moderate-intensity exercise is slowed in individuals with type 2 diabetes (T2D), at least in part due to limitations in O2 delivery. The present study tested the hypothesis that a prior heavy-intensity warm-up or 'priming exercise' (PE) bout would accelerate V̇O2 kinetics in T2D, due to a better matching of O2 delivery to utilisation. Twelve middle-aged individuals with T2D and 12 healthy controls (ND) completed moderate-intensity constant-load cycling bouts either without (ModA) or with (ModB) prior PE. The rate of muscle deoxygenation (i.e. deoxygenated haemoglobin and myoglobin concentration, [HHb+Mb]) and oxygenation (i.e. total oxygenation index, TOI) were continuously measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O2 delivery to O2 utilization was assessed by the Δ[HHb+Mb]/ΔV̇O2 ratio. Both groups demonstrated an accelerated V̇O2 kinetics response during ModB compared with ModA (T2D: 32±9 vs. 42±12 s; ND: 28±9 vs. 34±8 s), and an elevated muscle oxygenation throughout ModB, while the [HHb+Mb] amplitude was greater during ModB only in individuals with T2D. The [HHb+Mb] kinetics remained unchanged in both groups. In T2D ModB was associated with a decrease in the 'overshoot' relative to steady-state in the Δ[HHb+Mb]/ΔV̇O2 ratio (1.17±0.17 vs. 1.05±0.15), while no overshoot was observed in the control group prior to (1.04±0.12) or after (1.01±0.12) PE. Our findings support a favourable priming-induced acceleration of the V̇O2 kinetics response in middle-aged individuals with uncomplicated T2D attributed to an enhanced matching of microvascular O2 delivery to utilisation.