DOUBLY LABELED WATER MEASUREMENT OF HUMAN ENERGY-EXPENDITURE DURING EXERCISE AT HIGH-ALTITUDE

Estimates of total daily energy expenditure (TDEE) by the doubly label ed water (DLW, (H2O)-H-2-O-18) and intake balance (I-B) methods were c ompared in six male soldiers studied over 6 days that included 5 days of strenuous winter exercise at 2,500- to 3,100-m elevation. Use of bo dy energy stores [-9.54 +/- 1.54 (SD) MJ/day or -2,280 +/- 368 kcal/da y] was estimated from changes in body weight, body density (hydrodensi tometry), and total body water ((H2O)-O-18 dilution). The subjects wor e computerized activity monitors and kept daily records of ration cons umption (9.87 +/- 3.60 MJ/day or 2,359 +/- 860 kcal/day). Accuracy of individual DLW and I-B TDEE values was estimated from the correlations of TDEE with fat-free mass (FFM) or total weight (body wt + load). Th e DLW and I-B estimates of TDEE differed by -12.0 to 15.2% but provide d comparable estimates of group mean TDEE (DLW = 19.07 +/- 2.37 MJ/day or 4,558 +/- 566 kcal/day; I-B = 19.41 +/- 3.72 MJ/day or 4,639 +/- 8 89 kcal/day; P > 0.05). The DLW TDEE was correlated with both FFM (r(2 ) = 0.89, P < 0.01, power = 0.95) and total weight (r(2) = 0.95, P < 0 .01, power = 0.99), whereas I-B TDEE was correlated only with total we ight (r(2) = 0.75, P < 0.03, power = 0.81). Under adverse field condit ions the DLW method provided individual TDEE estimates that were proba bly more accurate than those provided by the I-B method.