Influence of priming exercise and type 2 diabetes on oxygen uptake and muscle deoxygenation kinetics during submaximal exercise

Middle aged and young adults with uncomplicated type 2 diabetes (T2D) show a slowed adjustment of oxidative metabolism during metabolic transitions (i.e. .oxygen uptake, VO2 kinetics) due to progressive limitations of both O2 delivery and utilisation. Priming exercise (PE) has been shown to increase the speed of adjustment of oxidative metabolism during subsequent moderate-intensity step transitions in healthy adults presenting initially slow VO2 kinetics. We tested the hypothesis that PE would increase the speed of the adjustment of the primary phase (taup, τp) of VO2 during moderate intensity cycling in T2D and that this would be due to a better matching of O2 delivery to utilisation. Ten middle-aged participants with uncomplicated T2D (50.7 ± 9.0 years, 30.4 ± 5.3 kg/m2; 7 men / 3 women) and 10 non-diabetic (ND) controls (44.4 ± 9.6 years, 31.1 ± 4.1 kg/m2; 7 men / 3 women) were recruited. Participants completed four bouts of constant-load cycling at 80% of their ventilatory threshold previously established during a ramp incremental test. Two of these constant-load bouts were completed without priming exercise (ModA) and two bouts were undertaken with prior heavy intensity priming exercise (ModB). VO2 kinetics was calculated from continuously measured breath-by-breath data, while the rate of muscle deoxygenation (i.e., deoxygenated hemoglobin, HHb) and tissue oxygen saturation (i.e., tissue oxygenation index) were continuously measured by Near-infrared spectroscopy (NIRS) at the vastus lateralis muscle. The time constant of the primary phase, τp, was significantly slower in T2D, but PE significantly (P