Use of the doubly labeled water technique in humans during heavy sustained exercise

TLDR

The study examines possible explanations for the systematic discrepancy between energy expenditure measured by doubly labeled water and by food records during prolonged cycling. Energy expenditure was quantified in four cyclists over consecutive 7–8 day intervals of the Tour de France using the doubly labeled water technique, with oral isotope doses achieving 200 ppm ^18O and 130 ppm ^2H, and isotope half‑lives of 2.25–3.80 days, while simultaneously recording dietary intake and monitoring body composition. The doubly labeled water method yielded higher energy expenditure values than food records, with the discrepancy increasing from 12.9 % to 35.3 % across intervals, and the cyclists’ average daily metabolic rates were 3.4–3.9 × or 4.3–5.3 × basal metabolic rate according to food records or DLW, indicating an energetic ceiling comparable to that of birds.

Abstract

We measured energy expenditure with the doubly labeled water technique during heavy sustained exercise in the Tour de France, a bicycle race lasting more than 3 wk. Four subjects were observed for consecutive intervals of 7, 8, and 7 days. Each interval started with an oral isotope dose to reach an excess isotope level of 200 ppm 18O and 130 ppm 2H. The biological half-lives of the isotopes were between 2.25 and 3.80 days. Energy expenditure was compared with simultaneous measurements of energy intake, and body mass and body composition did not change significantly. The doubly labeled water technique gave higher values for energy expenditure than the food record technique. The discrepancy showed a systematic increment from the first to the third interval, being 12.9 +/- 7.9, 21.4 +/- 9.8, and 35.3 +/- 4.4% of the energy expenditure calculated from dietary intake, respectively. Possible explanations for the discrepancy are discussed. The subjects reached an average daily metabolic rate of 3.4–3.9 or 4.3–5.3 times basal metabolic rate based on the food record technique and the doubly labeled water technique, respectively. Thus, when measured with the same technique, the energetic ceiling for performance in humans is comparable with that of animals like birds.