Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes

Abstract

We examined the variability and determinants of the respiratory exchange ratio (RER) at rest and during exercise in 61 trained cyclists. Fasting (10-12 h) RER was measured at rest and during exercise at 25, 50, and 70% of peak power output (W(peak)), during which blood samples were drawn for [lactate] and [free fatty acid] ([FFA]). Before these measurements, training volume, dietary intake and muscle fiber composition, [substrate], and enzyme activities were determined. There was large interindividual variability in resting RER (0.718-0.927) that persisted during exercise of increasing intensity. The major determinants of resting RER included muscle glycogen content, training volume, proportion of type 1 fibers, [FFA] and [lactate], and %dietary fat intake (adjusted r(2) = 0.59, P < 0.001). Except for muscle fiber composition, these variables also predicted RER at 25, 50, and 70% W(peak) to different extents. The key determinant at 25% W(peak) was blood-borne [substrate], at 50% was muscle [substrate] and glycolytic enzyme activities, and at 70% was [lactate]. Resting RER was also a significant determinant of RER at 25 (r = 0.60) and 50% (r = 0.44) W(peak).

Fat oxidation at rest predicts peak fat oxidation during exercise and metabolic phenotype in overweight men

“…The intensity at which peak fat oxidation occurs is within the range that can be expected for sedentary subjects 9,18 within L-RER group, whereas for H-RER group the exercise intensity is somewhat low compared with previously reported results. Plasma NEFA was positively correlated to peak fat oxidation in the overweight sedentary men, which is consistent with findings reported by Goedecke et al 10 in lean athletes.…”

“…18,30 Interestingly, peak fat oxidation in subjects having similar VO 2max shows a marked variation in both lean sedentary 9,29 and trained individuals. 10 In this study we show that also in overweight sedentary male subjects major heterogeneity amounting to a twofold difference in peak fat oxidation during exercise is present. The intensity at which peak fat oxidation occurs is within the range that can be expected for sedentary subjects 9,18 within L-RER group, whereas for H-RER group the exercise intensity is somewhat low compared with previously reported results.…”

“…9 In healthy lean young men both intra-and interpersonal variation of fat oxidation at rest persists through low and moderate exercise intensities, but not through high exercise intensity. 10 Data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2004 suggest that 51% of overweight and 32% of obese individuals exhibit a metabolically healthy phenotype. 11 It is not known why such a large proportion of overweight and obese individuals seem to avoid the metabolic derangements after obesity, but one possible mechanism is that a high peak fat oxidation capacity facilitates a metabolically healthy phenotype despite of overweight or obesity.…”

The potential for mitochondrial fat oxidation in human skeletal muscle influences whole body fat oxidation during low-intensity exercise

“…Previous studies have shown that there are large interindividual variations in FA utilization both at rest and during exercise (14,16), and there is evidence that FA oxidation is influenced by factors such as preceding diet, muscle glycogen content, exercise intensity, training status, training volume, and muscle fiber composition (14,51). A recent cross-sectional study of 300 subjects showed that a mere 12% of the variation in FA oxidation after 4-h fast could be explained by differences in training status, physical activity level, and sex, and it was concluded that differences in FA utilization between subjects remain largely unexplained (51).…”

Metabolismo energético em atletas de endurance é diferente entre os sexos

“…Tal fato justificaria uma possível diferença entre os sexos na recomendação de macronutrientes em esportes de longa duração. Contudo, outros autores não encontraram diferenças significativas, entre homens e mulheres, na proporção dos substratos utilizados durante o exercício [11][12][13][14][15][16][17][18][19] . Roepstorff et al 12 destacaram que a contribuição relativa de carboidratos e lipídeos como combustíveis, durante o exercício submáximo, é resultado da utilização dos diferentes carboidratos (glicose sangüínea e glicogênio muscular) e dos lipídeos (ácidos graxos de cadeia longa ligados à albumina plasmática, ácidos graxos dos triacilgliceróis presentes nas lipoproteínas de muito baixa densidade -VLDL-e ácidos graxos dos triacilgliceróis das células musculares).…”