Priming exercise accelerates oxygen uptake kinetics during high-intensity cycle exercise in middle-aged individuals...

Background: The primary phase time constant of pulmonary oxygen uptake kinetics ( $\stackrel{·}{V}{O}_2$ τ _p) during submaximal efforts is longer in middle-aged people with type 2 diabetes (T2D), partly due to limitations in oxygen supply to active muscles. This study examined if a high-intensity "priming" exercise (PE) would speed $\stackrel{·}{V}{O}_2$ τ _p during a subsequent high-intensity cycling exercise in T2D due to enhanced oxygen delivery. Methods: Eleven (4 women) middle-aged individuals with type 2 diabetes and 11 (4 women) non-diabetic controls completed four separate cycling bouts each starting at an 'unloaded' baseline of 10 W and transitioning to a high-intensity constant-load. Two of the four cycling bouts were preceded by priming exercise. The dynamics of pulmonary $\stackrel{·}{V}{O}_2$ and muscle deoxygenation (i.e. deoxygenated haemoglobin and myoglobin concentration [HHb + Mb]), were calculated from breath-by-breath and near-infrared spectroscopy data at the vastus lateralis, respectively. Results: At baseline $\stackrel{·}{V}{O}_2$ τ _p, was slower (p < 0.001) in the type 2 diabetes group (48 ± 6 s) compared to the control group (34 ± 2 s) but priming exercise significantly reduced $\stackrel{·}{V}{O}_2$ τ _p (p < 0.001) in type 2 diabetes (32 ± 6 s) so that post priming exercise it was not different compared with controls (34 ± 3 s). Priming exercise reduced the amplitude of the $\stackrel{·}{V}{O}_2$ slow component (A_s) in both groups (type 2 diabetes: 0.26 ± 0.11 to 0.16 ± 0.07 L/min; control: 0.33 ± 0.13 to 0.25 ± 0.14 L/min, p < 0.001), while [HHb + Mb] kinetics remained unchanged. Conclusion: These results suggest that in middle-aged men and women with T2D, PE speeds $\stackrel{·}{V}{O}_2$ τ _p likely by a better matching of O₂ delivery to utilisation and reduces the $\stackrel{·}{V}{O}_2$ A_s during a subsequent high-intensity exercise.