Aerobic fitness determines whole-body fat oxidation rate during exercise in the heat
Publication: Applied Physiology, Nutrition, and Metabolism
5 November 2010
Abstract
The purpose of this study was to determine whole-body fat oxidation in endurance-trained (TR) and untrained (UNTR) subjects exercising at different intensities in the heat. On 3 occasions, 10 TR cyclists and 10 UNTR healthy subjects (peak oxygen uptake = 60 ± 6 vs. 44 ± 3 mL·kg–1·min–1; p < 0.05) exercised at 40%, 60%, and 80% peak oxygen uptake in a hot, dry environment (36 °C; 25% relative humidity). To complete the same amount of work in all 3 trials, exercise duration varied (107 ± 4, 63 ± 1, and 45 ± 0 min for 40%, 60%, and 80% peak oxygen uptake, respectively). Substrate oxidation was calculated using indirect calorimetry. Blood samples were collected at the end of exercise to determine plasma epinephrine ([EPI]plasma) and norepinephrine ([NEPI]plasma) concentrations. The maximal rate of fat oxidation was achieved at 60% peak oxygen uptake for the TR group (0.41 ± 0.01 g·min–1) and at 40% peak oxygen uptake for the UNTR group (0.28 ± 0.01 g·min–1). TR subjects oxidized absolutely (g·min–1) and relatively (% of total energy expenditure) more fat than UNTR subjects at 60% and 80% peak oxygen uptake (p < 0.05). At these exercise intensities, TR subjects also had higher [NEPI]plasma concentrations than UNTR subjects (p < 0.05). In the heat, whole-body peak fat oxidation occurs at higher relative exercise intensities in TR than in UNTR subjects (60% vs. 40% peak oxygen uptake). Moreover, TR subjects oxidize more fat than UNTR subjects when exercising at moderate to high intensities (>60% peak oxygen uptake).
Résumé
Cette étude se propose d’analyser le degré d’oxydation des gras dans tout l’organisme de sujets entraînés en endurance (TR) et de sujets non entraînés en endurance (UNTR) au cours d’exercices accomplis à différentes intensités dans un environnement chaud. En trois occasions, 10 cyclistes TR et 10 sujets UNTR en bonne santé (consommation d’oxygène de pointe = 60 ± 6 mL·kg–1·min–1 comparativement à 44 ± 3 mL·kg·–1min–1; p < 0,05) font un effort dans un environnement chaud (36 °C; 25 % HR), et ce, aux intensités suivantes : 40 %, 60 % et 80 % du consommation d’oxygène de pointe. Afin de maintenir constante la quantité de travail accompli, la durée des efforts varie comme suit : 107 ± 4 min, 63 ± 1 min et 45 ± 0 min pour les intensités respectives de 40 %, 60 % et de 80 % du consommation d’oxygène de pointe. On mesure le degré d’oxydation des gras par calorimétrie indirecte. À la fin des séances d’exercice, on prélève des échantillons sanguins pour en déterminer les concentrations plasmatiques d’épinéphrine ([EPI]plasma) et de norépinéphrine ([NEPI]plasma). On enregistre le plus haut taux d’oxydation des gras chez les TR à 60 % du consommation d’oxygène de pointe (0,41 ± 0,01 g·min–1) et, chez les UNTR, à 40 % du consommation d’oxygène de pointe (0,28 ± 0,01 g·min–1). Les sujets TR oxydent plus de gras que les sujets UNTR en valeur absolue (g·min–1) et en valeur relative (% du total d’énergie dépensée) à 60 % et 80 % du consommation d’oxygène de pointe (p < 0,05). À ces intensités d’exercice, la [NEPI]plasma chez les sujets TR est plus élevée que chez les sujets UNTR (p < 0,05). Dans un environnement chaud, l’oxydation des gras dans l’organisme se manifeste chez les sujets TR à une plus haute intensité relative : 60 % comparativement à 40 % du consommation d’oxygène de pointe chez les UNTR. De plus, les sujets TR oxydent plus de gras que les sujets UNTR au cours d’efforts d’intensité modérée à élevée (>60 % du consommation d’oxygène de pointe).
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Applied Physiology, Nutrition, and Metabolism
Volume 35 • Number 6 • December 2010
Pages: 741 - 748
History
Received: 8 April 2010
Accepted: 12 August 2010
Version of record online: 5 November 2010
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JuanDel CosoJ. Del Coso, NassimHamoutiN. Hamouti, Juan FernandoOrtegaJ.F. Ortega, and RicardoMora-RodriguezR. Mora-Rodriguez. 2010. Aerobic fitness determines whole-body fat oxidation rate during exercise in the heat. Applied Physiology, Nutrition, and Metabolism. 35(6): 741-748. https://doi.org/10.1139/H10-068