The effect of type 2 diabetes in muscle deoxygenation during ramp incremental cycling exercise

Defects in functional exercise capacity in patients with type 2 diabetes mellitus (T2DM) have been consistently reported, with impairments in maximal exercise performance of ~20% that are independent of obesity, and present in the absence of clinically apparent cardiovascular disease. Whilst the precise mechanisms for this abnormal exercise response remain to be elucidated, both central and peripheral factors have been identified as potential contributors (Green et al, 2015). In the present study we tested the hypothesis that T2DM alters the profile of muscle fractional O2 extraction (estimated using deoxygenated haemoglobin) during incremental cycle exercise. Eight middle-aged participants (6 men, 2 women) with T2DM (46.85±7.58yrs; 31.68±5.76kg/m2) and eight healthy controls (6 men, 2 women) (42.33±7.56yrs; 30.4±2.22kg/m2) matched for age and body mass index respectively, performed a ramp incremental cycling test to exhaustion in an upright position. Exercise was performed initially for 2-min at 10W, followed by 15 W/min (females) or 25 W/min (males) increments on an electrically braked cycle ergometer, with pedal frequency held constant at an individually selected rpm. Pulmonary oxygen uptake (VO2) was measured on a breath-by-breath basis using an online metabolic system. The rate of muscle deoxygenation (i.e. deoxygenated haemoglobin concentration, Δ[HHb]) profiles of the vastus lateralis (VL) muscle were continuously made with near infrared spectroscopy (NIRS) and analysed with a double linear model. Values are means ± SD, compared by a paired t test. Normalised VO2peak was significantly (P = 0.047) reduced in individuals with T2DM compared with their respective non-diabetic counterparts (24.52 ± 4.15 vs 29.52 ± 4.99), representing a 17% reduction in peak exercise capacity. The first slope of the double linear regression function used to establish the dynamic adjustment of [HHb], was significantly (P = 0.038) larger in participants with T2DM than controls (1.35 ± 0.17 vs 1.08 ± 0.35). Such findings are indicative of a greater rate of oxygen extraction for a given increase in VO2, suggesting that a reduced O2 delivery is an important underlying cause of exercise intolerance during a maximum graded test in T2DM.