Metabolic Inflexibility in the Acute Exercise Response of Type 2 Diabetics

PURPOSE: Metabolic flexibility (MF) has been defined as the ability to match fuel use to fuel availability. It is suggested that MF is diminished in type 2 diabetes and in obese, insulin-resistant adults, and that this is related to the accumulation of intramuscular lipids. Chronic exercise training has been shown to improve MF in response to hyperinsulinemic clamping and acute or chronic feeding of high-fat or high carbohydrate diets in type 2 diabetics, but MF responses to acute exercise bouts have not been investigated. METHODS: 16 overweight males [8 control (CON), 8 type 2 diabetic (T2D)] participated in this study. Subjects completed an incremental treadmill test from which an estimated VO2max was obtained, and workloads corresponding to 25%, 35% and 45% of estimated VO2max were calculated. On a separate visit after an overnight fast, fasted respiratory exchange ratio (RER) was obtained by indirect calorimetry, as an average over 10 minutes of measurement after 15 minutes of supine rest. Subjects then completed a 6 minute steady-state exercise bout on the treadmill at each of the pre-determined individualised intensities. ΔRER was calculated as the difference between fasted and steady-state exercise RER. Data are presented as means ±SD. Between group differences were analysed by unpaired Student’s T-test, with significance set at p < 0.05. RESULTS:CON were younger (51±5.7 vs 59 ±6.4 years) and fitter (37.2±3.6 vs 30.2±8.1 ml/kg/min estimated VO2max) than T2D, with no difference in BMI (32.2 ±5.1 vs 30.7 ±1.4 kg/m2). T2D had significantly higher glycosylated haemoglobin (7.7 ± 0.8 vs 5.7 ±0.3 %) and fasting plasma glucose (8.6 ± 1.5 vs 5.2 ±0.6 mmol/L) than CON. There was no difference in resting RER between the groups (T2D 0.79 vs CON 0.78). Exercise RER was consistently higher in CON than T2D, and this was reflected by significant differences in ΔRER at the 25% and 35% intensities (25%: -0.03 vs 0.09, 35%: -0.02 vs 0.05) and a non-significant difference at 45% (-0.06 vs -0.03). CONCLUSION:These data suggest that individuals with type 2 diabetes have impaired MF in response to acute submaximal exercise challenges, relative to healthy controls.