Conference Publication Details
Mandatory Fields
Brian P. Carson, Gabriella F. Bellissimo, Jeffery J. Betts, Jeffrey E. Edwards
Medicine & Science in Sports & Exercise, 46(5S):157-161
A preliminary investigation into the effect of exercise on metabolic flexibility using a novel methodology
Optional Fields

Metabolic flexibility is termed the body’s ability to adapt fuel oxidation to fuel availability and demand. Metabolic inflexibility, whereby the capacity to switch between fat and glucose oxidation in response to a meal is impaired and preference is for glucose oxidation in the fasted state has implications for metabolic diseases such as obesity and type 2 diabetes. 

Purpose: To assess the effect of acute aerobic exercise on metabolic flexibility using a novel methodology.

Methods: Following ethical approval, six subjects (age, 30.7±11 yrs; height, 174±9 cm; weight, 73.7±12.7) agreed to participate in the study. Baseline Dual X-Ray absorptiometry (DXA) (body fat, 21.23±10.02%) and maximal oxygen uptake (VO2max, 49.5±10.2 measurements were performed. During an evening visit subjects underwent either 45 mins of seated rest (REST) or treadmill exercise at 70% VO2max (EX) followed by a standardized mixed meal. The next morning, 10hrs postprandial, subjects consumed another mixed meal containing 30% of daily BMR calculated using the Harris Benedict equation. Serial blood and respiratory gas samples were collected pre, 30, 60, 90, and 120 mins post meal. Individual variances for insulin and RQ in response to the meal were determined and used to establish metabolic flexibility, whereby, higher variance in RQ and lower variance in insulin represent greater metabolic flexibility.

Results: The variance in RQ (REST, 0.00016±0.0011; EX, 0.0016±0.0008; p=0.753) and insulin (REST, 14761±9542; EX, 11961±8293; p=0.345) in response to the mixed meal did not differ significantly between the REST and EX conditions. Similarly, no significant differences were observed between REST and EX conditions for fasting RQ (REST, 0.79±0.05; Ex, 0.79±0.03; p=0.6) or Area Under Curve for Insulin (REST, 19667±9680; EX, 15304±6331; p=0.173).

Conclusions: We hypothesized that an enhanced metabolic flexibility in response to a mixed meal would result from a previous exercise bout when compared to rest. This was defined as increased variance in RQ and improved insulin sensitivity i.e. a decrease in variance and/or AUC for insulin. As there was no difference between conditions in these variables we conclude that metabolic flexibility, as measured in this study, is not enhanced after acute aerobic exercise.

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