Effect of type 2 diabetes in muscle deoxygenation during ramp incremental exercise in older individuals

Peak oxygen uptake (VO_2peak) in people with type 2 diabetes (T2D) of all ages is significantly lower than in healthy individuals (Green et al. 2015). In middle-aged individuals with T2D (< 55yrs) there appears to be an over reliance in fractional oxygen extraction during maximal ramp incremental exercise (RI), reflected by an increased rate of muscle deoxygenation (i.e., deoxygenated haemoglobin and myoglobin, [HHb+Mb]) (Gildea et al. 2016).To better understand the reduced VO_2peak responses observed in older individuals (>60 yrs) with uncomplicated T2D the present study investigated whether T2D also alters the profile of muscle fractional O₂ extraction in older individuals with uncomplicated T2D during incremental cycling exercise. Twelve older participants (9 men, 3 women) with T2D (age: 63.0 ± 2.9 yrs range: 59.8 – 67.4 yrs; BMI: 29.2 ± 4.1 kg.m^-2) and twelve older healthy controls (9 men, 3 women) (age: 64.5 ± 3.9 yrs range: 59.3 – 68.2 yrs; BMI: 27.5 ± 2.8 kg.m^-2) took part in the study. Each participant completed a ramp incremental cycling test to volitional exhaustion in an upright position followed by a verification test. Exercise was performed on an electrically braked cycle ergometer with participants initially exercising for 2-min at 10W before the intensity increased by 10-15W.min^-1 for women and 15-20W.min^-1 for men. Pulmonary oxygen uptake (VO₂) was measured on a breath-by-breath basis with an online metabolic system while muscle deoxygenation was assessed using near-infrared spectroscopy (NIRS) at the vastus lateralis muscle. Normalised [HHb+Mb] profiles ([HHb+Mb]%) were plotted as a function of relative work rate (%POpeak) using a bilinear model. Physiological variables were compared using unpaired t-tests or Mann-Whitney U tests with statistical significance set at P < 0.05. Values are means ± SD. Normalised VO_2peak was significantly (P < 0.05) reduced in the older individuals with T2D compared with the heathy older controls (23.9 ± 4.1 mL.kg.min^-1 vs 27.2 ± 5.3 mL.kg-1.min^-1), representing a 12% reduction in peak exercise capacity. There was no difference in the slope of the first linear component of the ∆[HHb+Mb]% vs ∆%POpeak profile (S₁) between the 2 groups (Controls: 1.82 ± 0.8 a.u vs T2D: 1.81 ± 0.6 a.u.). Such findings are suggestive that in contrast to middle-aged individuals with T2D, a greater rate of oxygen extraction for a given increase in VO₂, indicative of reduced O₂ delivery, is not a contributing factor to the reduction in VO_2peak observed in older individuals with T2D compared to healthy controls.
Gildea N, Rocha J, O’Shea D, Green S & Egaña M (2016). The effect of type 2 diabetes in muscle deoxygenation during ramp incremental exercise. Poster communication, Biomedical Basis of Elite Performance, East Midlands Conference Centre, Nottingham, UK.
Green S, Egana M, Baldi C, Lamberts R & Regensteiner J (2015). Cardiovascular control during exercise in type 2 diabetes mellitus. J Diabetes Res 2015, 1-11.