Muscle deoxygenation during ramp incremental cycle exercise in older adults with type 2 diabetes

Abstract

Purpose: To explore profiles of fractional O₂ extraction (using near-infrared spectroscopy) during ramp incremental cycling in older individuals with type 2 diabetes (T2D).

Methods: Twelve individuals with T2D (mean ± SD, age: 63 ± 3 years) and 12 healthy controls (mean age: 65 ± 3 years) completed a ramp cycling exercise. Rates of muscle deoxygenation (i.e., deoxygenated haemoglobin and myoglobin, Δ[HHb + Mb]) profiles of the vastus lateralis muscle were normalised to 100% of the response, plotted against absolute (W) and relative (%_peak) power output (PO) and fitted with a double linear regression model.

Results: Peak oxygen uptake (V̇O_2peak) was significantly (P < 0.01) reduced in T2D (23.0 ± 4.2 ml.kg^-1.min^-1) compared with controls (28.3 ± 5.3 ml.kg^-1.min^-1). The slope of the first linear segment of the model was greater (median (interquartile range)) in T2D (1.06 (1.50)) than controls (0.79 (1.06)) when Δ%[HHb + Mb] was plotted as a function of PO. In addition, the onset of the second linear segment of the Δ%[HHb + Mb]/PO model occurred at a lower exercise intensity in T2D (101 ± 35 W) than controls (140 ± 34 W) and it displayed a near-plateau response in both groups. When the relationship of the Δ%[HHb + Mb] profile was expressed as a function of %PO no differences were observed in any parameters of the double linear model.

Conclusions: These findings suggest that older individuals with uncomplicated T2D demonstrate greater fractional oxygen extraction for a given absolute PO compared with older controls. Thus, the reductions in V̇O_2peak in older people with T2D are likely influenced by impairments in microvascular O₂ delivery.

Keywords: Ageing; Cycling; Exercise tolerance; Near-infrared spectroscopy; Oxygen extraction; Type 2 diabetes.