Plasma glycerol during the acute post-exercise recovery period: Influence of exercise intensity

Abstract

Intensity of exercise can influence substrate utilization, with increasing intensity resulting in lower rates of fat oxidation and the reliance on carbohydrate as the preferred fuel. Fat oxidation (or more specifically, mobilization) can be assessed via the measurement of circulating glycerol, with most prior research focusing on aerobic exercise and measurements obtained during the actual exercise bout. The present study determined the degree of fat oxidation/mobilization by measuring plasma glycerol concentrations during the one hour post-exercise recovery period following three difference exercise bouts. On four different days, exercise trained men (n=12; 23.7±1.1 years) either rested quietly or performed aerobic cycle exercise (60 min at 70% heart rate reserve), 60 s cycle sprints at 100% max wattage obtained during graded exercise testing (GXT) - a total of five, or 15 s cycle sprints at 200% max wattage obtained during GXT - a total of 10. Blood was collected before and at 1, 30 and 60 min post-exercise. Haematocrit and haemoglobin were measured to correct for changes in plasma volume. Glycerol was analysed in plasma and the area under the curve was calculated. Glycerol increased across time (P < 0.0001) from pre-exercise (8.4±0.3 μg/dl) to 1 min (13.1±0.7 μg/dl), 30 min (11.3±0.6 μg/dl) and 60 min (9.1±0.5 μg/dl) post-exercise, with 1 min and 30 min post-exercise greater than pre-exercise and 60 min post-exercise (P < 0.05). Area under the curve was greater (P=0.0004) for aerobic exercise (24.7±2.0 μg/dl/h), 60 second sprints (23.4±1.9 μg/dl/h) and 15 sec sprints (24.4±1.5 μg/dl/h), as compared to rest (15.3±0.8 μg/dl/h), with no differences noted between exercise bouts (P > 0.05). All exercise bouts increase circulating glycerol, with no differences noted between bouts. Although previous data indicate that low intensity aerobic exercise results in greater fat oxidation than high intensity exercise (when assessed during the actual exercise session), our findings suggest that high intensity exercise may result in similar fat oxidation/mobilization as compared to aerobic exercise during the acute post-exercise period.

Publication Title

Comparative Exercise Physiology

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