Sex difference in substrate oxidation during low-intensity isometric exercise in young adults

Abstract

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 (<4 METs) 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. 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, +25 kg) in 26 healthy, young adults. Nine participants repeated the experiment on 3 separate days to assess within-subject, between-day variability. There was no significant difference in energy cost and heart rate responses to low-intensity isometric exercise (<2 METs) between men and women. However, a sex 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 sex 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 sexes. These results suggest that 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.

Gender in Endocrine Diseases: Role of Sex Gonadal Hormones

“…In particular, estrogens mainly act through estrogen receptor-alpha in the skeletal muscle to stimulate the genomic expression of proteins to increase the availability of long chain fatty acids (LCFA) improving adipocyte lipolysis and increasing intramyocellular lipid storage. Following on, estrogens affect fuel metabolism during exercise by nongenomic means to increase the activation of 5′ adenosine monophosphate-activated protein kinase (AMPK) [ 16 , 98 ].…”

Gender‐specific considerations in physical activity, thermogenesis and fat oxidation: implications for obesity management

“…Daily‐life physical activities generally increase EE no more than four times that of resting and represent a feasible alternative to sedentary behaviour , being of an intensity low enough to maximize compliance but still capable of enhancing fat oxidation . However, the metabolic response to such low level activity is often overlooked in preference for activities in the higher intensity zone.…”

“…A number of such activities have recently been investigated, with no difference found in terms of either energy cost or substrate utilization between men and women during posture maintenance or low‐power cycling . However, an important difference in terms of substrate oxidation in response to a standardized low‐intensity isometric leg press was observed – with men increasing both fat and carbohydrate oxidation during the activity, but women only increasing fat oxidation while maintaining carbohydrate oxidation at baseline, resting levels. There was no difference in terms of energy cost between the two genders.…”

Standing economy: does the heterogeneity in the energy cost of posture maintenance reside in differential patterns of spontaneous weight-shifting?

“…EE was calculated according to the Weir equation (Weir 1949): EE = 5.68 VO 2 + 1.59 VCO 2 − 2.17 N u , where N u is the total urinary nitrogen excreted. As short-term urinary collections to assess total N u may not be representative of the protein oxidised during the measurement itself, they were not obtained in this study, and assumed to be 13 g/24 h, as described previously Fares et al 2016;Sarafian et al 2016).…”