Gender difference in substrate oxidation during low-intensity isometric exercise in young adults.
Delphine Sarafian Applied Physiology, Nutrition, and Metabolism May 2016.
Purpose: Low-intensity physical activity is increasingly promoted as an alternative to sedentary behavior. However, much research to-date has focused on moderate-to-vigorous intensity physical activity, and in particular dynamic work, with the effect of low-intensity isometric exercise (<4METs) on substrate utilization yet to be explored. Here we investigate the effects of such exercise on respiratory quotient (RQ) and determine the extent of intra- and inter-individual variability in response.
Methods: Energy expenditure, RQ and substrate oxidation were measured by ventilated-hood indirect calorimetry at rest and in response to standardized, intermittent, low-level isometric leg-press exercises at 5 loads (+5, +10, +15, +20, +25kg) in 26 healthy, young adults. Nine participants repeated the experiment on 3 separate days to assess within-subject, between-day variability.
Results: There was no significant difference in energy cost and heart rate responses to low-intensity isometric exercise (<2METs) between men and women. However, a gender difference was apparent in terms of substrate oxidation – with men increasing both fat and carbohydrate oxidation, and women only increasing fat oxidation while maintaining carbohydrate oxidation at baseline, resting levels. This gender difference was repeatable and persisted when substrate oxidation was adjusted for differences in body weight or body composition. Individual variability in RQ was relatively low, with both intra- and inter-individual coefficients of variation in the range of 3-6% in both genders.
Conclusions: These results suggest women preferentially increase fat oxidation during low-level isometric exercise. Whether such physical activity could be incorporated into treatment/prevention strategies aimed at optimizing fat oxidation in women warrants further investigation.
