Physical Fitness and Performance Energy expenditure during 2 wk of an ultra- endurance run around Australia REBECCA J. HILL and PETER S. W. DAVIES School of Human Movement Studies, Faculty of Health, Queensland University of Technology, Brisbane, Queensland, AUSTRALIA; and Children’s Nutrition Research Centre, Department of Paediatrics and Child Health, Royal Children’s Hospital, Binsbane, Queensland, Australia. ABSTRACT HILL. R. J., and P. S. W. DAVIES. Energy expenditure during 2 wk of an ultra-endurance run around Australia. Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 148 –151. Purpose: For ultra-endurance athletes, whose energy expenditure is likely to be at the extremes of human tolerance for sustained periods of time, there is increased concern regarding meeting energy needs. Due to the lack of data outlining the energy requirements of such athletes, it is possible that those participating in ultra-endurance exercise are compromising performance, as well as health, as a result of inadequate nutrition and energy intake. To provide insight into this dilemma, we have presented a case study of a 37-yr-old ultra-marathon runner as he runs around the coast of Australia. Methods: Total energy expenditure was measured over a 2-wk period using the doubly labeled water technique. Results: The average total energy expenditure of the case subject was 6321 kcald -1 . Based on the expected accuracy and precision of the doubly labeled water technique the subject’s total energy expenditure might range between 6095 and 6550 kcald -1 . The subject’s average daily water turnover was 6.083 L over the 14-d period and might range between 5.9 L and 6.3 Ld -1 . Conclusions: This information will provide a guide to the energy requirements of ultra-endurance running and enable athletes, nutritionists, and coaches to optimize performance without compromising the health of the participant. Key Words: ENERGY REQUIREMENTS, WATER TURNOVER, DOUBLY LABELED WATER I nadequate nutrition and energy intake has detrimental effects on both sport performance and general health. For ultra-endurance athletes, whose energy expenditure (EE) is likely to be at the extremes of human tolerance for sustained periods of time, there is increased concern regard- ing meeting their energy needs. This is especially apparent as research outlining the EE and thus, requirements, of athletes in ultra-endurance sports is scarce, possibly due to the fact that, until recently, there were no methods available to measure EE over long periods of time without placing major restrictions on the activity of the athlete. In the 1980s, the advent of the doubly labeled water (DLW) technique made it possible to measure EE in so called “free-living” populations (19). This involves the in- gestion of the stable isotopes 2 H and 18 O as water, and the subsequent measurement of their enrichment, using isotope ratio mass spectrometry, in bodily fluids such as saliva, urine, or plasma. The difference between the elimination rates of the two isotopes is used to determine carbon dioxide production rate and hence, EE (20). Additionally, the elim- ination rate of 2 H is representative of water turnover and therefore fluid requirements may also be determined. Using this technique, Schulz et al. (22) assessed the energy requirements of nine elite female distance runners over a 6-d period. Their subjects average daily free-living EE was 2826 kcal with a training load of approximately 16.1 kmd -1 . Edwards et al. (7) also studied female endurance runners and found that the average daily energy require- ments of the nine women studied, while training approxi- mately 10.5 kmd -1 , was 2991 kcal. It must be noted, how- ever, that both these studies, although using distance runners as subjects, were not performed during an actual endurance event but rather, during usual training. In contrast, Wester- terp et al. (25) measured the EE of four cyclists while they competed in the Tour de France, an event that runs over 3 wk. The authors documented an average daily EE of 7027 kcal (29.4 MJ) and 8604 kcal (36.0 MJ) for weeks 1 and 2, respectively, and 8532 kcal (35.7 MJ) for week 3. In com- parison, the average daily EE of a sedentary man of similar age and height is about 2390 kcal (10 MJ). Although it is possible to extrapolate the results of Wes- terterp et al. (25) and apply them to ultra-endurance running, as different muscle groups are used during cycling, it would only be an estimation of the energy requirements. No studies of the like have been performed with male ultra-endurance runners as subjects. 0195-9131/01/3301-0148/$3.00/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2001 by the American College of Sports Medicine Received for publication January 2000. Accepted for publication April 2000. 148