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APPLIED SCIENCES: Physical Fitness and Performance

Energy expenditure during 2 wk of an ultra-endurance run around Australia


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Medicine and Science in Sports and Exercise: January 2001 - Volume 33 - Issue 1 - p 148-151
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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 regarding 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 ingestion of the stable isotopes 2H and 18O 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 elimination rate of 2H 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 requirements of the nine women studied, while training approximately 10.5 km·d-1, was 2991 kcal. It must be noted, however, 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, Westerterp 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 comparison, 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 Westerterp 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.

A case study of a 37-yr-old ultra-marathon runner is presented in this paper. The aim of this research was to provide insights into the energy requirements of ultra-endurance running utilizing the DLW technique and further, outline the extent of water turnover of such an undertaking.


Subjects and procedures.

The male subject began his run around Australia in Canberra in May 1999 with the aim of completing over 14,500 km in less than 217 d. This goal therefore required an average of 70–90 km·d-1 running to be covered with no days for rest. The subject has a history of similar sporting achievements including holding the world record for running across the Simpson Desert in Australia and vertical distance running, as well as being a twice participant in the Trans American Ultra-marathon, which races from California to New York. The subject was self-selected to participate in the round Australia run and initial contact was via the University of Sydney. Written consent was obtained from the subject and the project was approved by the Queensland University of Technology Ethics Committee.

The subject was dosed with DLW in Newcastle, NSW, at the commencement of the 2nd week of the run and was met periodically as he traveled 992 km to the sample collection destination of Caloundra, QLD. Telephone contact was maintained throughout the 2-wk study period to promote compliance and minimize any inconveniences with respect to the runner himself and his support crew. To assess whether changes in background water supply would affect the measurement of total EE, samples of drinking water were also requested at 2-d intervals.

Total EE was measured using the DLW technique. Two stable, non-radioactive, non-toxic isotopes of hydrogen (deuterium, 2H) and oxygen (18O) in the form of water, i.e., 2H2O and H218O, were administered to the subject. The subject consumed 0.05 g·kg-1 of body weight of deuterium (100%) and 1.25 g·kg-1 of body weight 18O (10%), administered via a 200-mL glass bottle (Schott) and drinking straw. The dose consumed was recorded to two decimal places of a gram. A single urine sample was obtained before the dose, and subsequently urine samples were collected 4–6-h post-dose and thence every 24-h for the following 14-d. All samples were collected in 20-mL Universal tubes and subsequently frozen. The subject was instructed to record the time each urine sample was collected.

The enrichment of both the deuterium and 18O samples were measured in triplicate via isotope ratio mass spectrometry (Hydra, PDZ Europa, UK), with the results being expressed in delta (δ) units as %0 (per mil) relative to standard mean ocean water (SMOW).

The dilution space of each isotope (No, Nd) was determined using a modification of the equation developed by Halliday and Miller (12) :


where N is either Nd, the deuterium dilution space or No, the 18O dilution space (in grams). A is the amount of isotope given to the subject in grams, a is the portion of the dose (in grams) retained for mass spectrometer analysis, T is the amount of tap water in which portion a is diluted before analysis, and Ea, Et, and Es are the isotopic enrichments in delta units relative to SMOW of the portion of dose, the tap water used, and the intercept of the log of enrichment against time, respectively.

The elimination rates of 2H and 18O, kd and ko, respectively, were determined by plotting the log transforms of the measured enrichments minus the predose sample of deuterium and 18O in the urine against time expressed as decimal days. Carbon dioxide production rate was therefore determined as previously described (5,6). A respiratory quotient (RQ) of 0.85 was assumed for the subject. This value is indicative of the catabolism of a mixed diet (17). Oxygen consumption was hence determined and total EE was then calculated using Weir’s (24) formula.

Water turnover was calculated using the following equation:


where Nd is the deuterium dilution space and kd is the elimination rate of deuterium.

The physical activity level (PAL) of the subject was calculated by dividing total EE by basal metabolic rate (BMR). BMR was estimated using the following equation of Schofield et al. (21) :



The age, weight, and height of the subject was 37 yr, 63.1 kg, and 171 cm, respectively. The isotopic data is shown in Table 1. The dilution space for 18O was 52545.0 mL and for 2H, 52957.6 mL. The respective elimination rates of 18O and 2H were 0.1573 and 0.1195. Daily total EE was calculated as 6321 kcal and the average daily water turnover was 6.083 L. According to Cole and Coward (4), the precision and accuracy of the DLW technique using the multipoint method, as was used in this study, is approximately 3.6%. Thus, the average daily EE of the subject ranged between 6095 kcal and 6550 kcal, and on average his water turnover was between 5.9 L and 6.3 L·d-1. The subject’s estimated BMR was 1597 kcal, and hence his PAL was determined as 3.96.

Table 1
Table 1:
Subject isotopic enrichment data where No and Nd are the dilution spaces of18O and 2H respectively, and ko and kd are the disappearance rates of 18O and 2H respectively.


The energy requirements and water turnover of a 37-yr-old ultra-marathon runner were assessed using the DLW technique over a 2-wk period during a 7-month run around Australia. The run was completed by the subject in a record 195-d (6 months, 12-d) with a total of 14,964 km being covered. The subject ran each day of this period and on average completed 76.74.

Two of the major factors affecting ultra-endurance performance, as well as short and long term general health, are adequate calorie intake and hydration. The deleterious effects of inadequate nutrition are well documented and include serious physiological consequences, such as ketonuria; hypoglycemia; decreased urinary output; weakness; fainting; loss of electrolytes, minerals, and lean tissue; glycogen depletion; and increased injury rates (1). Obviously, these consequences may in turn affect performance.

In Australia, it is recommended men of similar age, height, and weight to the case subject consume approximately 2250–2600 kcal·d-1(16). As this recommendation is based on a PAL representative of light work (1.4–1.6) and BMR estimated from equations by Schofield et al. (21), it was expected that the energy requirements measured in this study would be substantially higher. Supporting this belief, the average daily total EE, and hence requirement, of our subject was 6321 kcal (PAL = 3.96), significantly higher that the national allowance. Even when a higher PAL is the basis of the RDA, as is with the International Recommendation of 3600 kcal·d-1(8), the requirement of our subject was still much greater.

Attempts were made to obtain an insight into the energy balance of the subject over the study period by requesting food records be kept however, the validity of the subsequent diet records was questionable, and hence it was not possible to accurately ascertain energy intake (EI). The subject’s loss of body weight over the study period (1.5 kg) does, however, indicate that negative energy balance ensued. Upon completion of the 195-d run the subject had lost a total of 1 kg of body weight compared with that measured at commencement, and hence this suggests that there was not a significant energy deficit during the run.

As a corollary of the unavailability of diet records, it was necessary to assume a respiratory quotient rather than determine one based on diet composition. It is possible, that as the subject was supplementing his carbohydrate intake, assuming a respiratory quotient representative of the catabolism of a mixed diet (0.85) may not be appropriate. However, in effect, changing the respiratory quotient to, for example, 0.90, changes the subject’s calculated EE by only −4.4%. Thus, an alteration of this size still falls close to the range of the subject’s EE as determined by the precision and accuracy of the DLW technique (3.6%).

For several reasons, it is difficult to make comparisons between the present study’s results and the recommendations make by previous authors. First, of the very few studies conducted using the DLW technique in runners, the subjects were female and hence it would not be appropriate to make a direct comparison. Second, this paper is the first to assess EE during ultra-endurance running. As previously mentioned, Westerterp et al. (25) measured the energy requirements of male cyclists in the Tour de France competition; however, it would be inappropriate to assume the energy requirements of cycling would be applicable to running. As with the aforementioned, the findings of Sjödin et al. (23), who studied cross-country skiers during training, although ultra-endurance, are also not applicable to running. These are however, the only studies to report high EE values similar to our case subject. The reported EEs were 8054 and 7218 kcal·d-1 by Westerterp et al. (25) and Sjödin et al. (23), respectively.

Research has shown, that at levels of dehydration as low as 3% body weight, work performance decreases and physiological indices of stress increase (15). Dehydration causes impaired aerobic capacity (3); reduced venous return and stroke volume and a concomitant increase in heart rate; decreased cardiac output; reduced plasma volume (17); decreased peripheral circulation (10) and hence decreased sweating rate (18); and an increase core temperature (11). Conversely, adequate hydration reportedly has a glycogen sparing effect by preventing an elevated core temperature initiated shift to reliance on carbohydrate metabolism and thereby, prolonging endurance exercise (9,13). Knowledge of the extent of water turnover during prolonged exercise is therefore critical to both the health and safety, and performance, of ultra-endurance athletes.

To date, there is no literature outlining the water turnover, and hence requirements, of ultra-endurance runners. This is, of course, related to the absence of DLW studies involving these athletes. Unfortunately, it is not even possible to effectively compare our results with the few studies aforementioned involving female runners and cross-country skiers as no data are given that would allow water turnover calculation. Dilution spaces and elimination rate constants are, however, reported by Westerterp et al. (25). At day 16 of the Tour de France, the cyclists water requirements were 10.48 L, almost 1.7 times that of our subject’s requirement (6.08 L). Again, these reports are not directly comparable however, due to the physiological differences between cycling and running.

It has previously been reported that the components of normal foods (2) and drinking water (26) are subject to isotopic abundance variations. This does not pose a particular problem when normal mixed diets are consumed (14) however, with changes in nutrition, in particular the consumption of water from different sources or geographical regions, changes in background isotope levels may occur, and in turn the accuracy of the DLW technique may be compromised. We speculated that, as our subject was not geographically stationary during the testing period, he would possibly be consuming water of differing isotopic enrichments. However, although measures were taken to compensate for this, that is, drinking water samples were requested every second day, in reality the subject consumed the same brand bottled water from the start of his run and over the study period and thus it was not necessary to make adjustments.

Under extreme exercise conditions, as was undertaken by the subject in this study, there is the potential that certain assumptions associated with the DLW technique may not be upheld. Thus, in effect, the durability of the method was also under investigation during this research.

With respect to the constancy of the total body water pool, changes in body weight need to be taken into account. Over the study period, the subject lost a total of 1.5 kg of body weight, or −2.4%. However, a 2.4% alteration in total body water only equates to a change in calculated EE of 2% (123 kcal·d-1), which is within the accuracy and precision of the technique itself.

Within the calculation of EE, isotopic fractionation must be taken into account. There are a number of ways in which this can be done, and we have used probably the simplest approach of assuming a value of 0.25 as the proportion of water output that is fractionated. This value has been used in studies on free-living individuals on many occasions. However, in the study described here, it is possible that the assumptions that underlie the choice of 0.25 as the proportion of water fractionated will not hold. It may be postulated that as a result of increased water turnover, especially via lung losses, the proportion of water fractionated might increase. Nevertheless, it is highly likely that nonfractionated water losses, notably sweat, will also increase and thus the proportion of fractionated water loss may not rise as much as first thought. Even if the proportion of water fractionated did rise as high as 0.5, which we believe is unlikely, the subject’s total EE would only reduce by 5% (343 kcal·d-1).

In conclusion, we have presented a case study of a 37-yr-old ultra-marathon runner with the aim of providing insights into the energy requirements of ultra-endurance running and further, outline the extent of water turnover of such an undertaking. As the subject ran, on average, the same kilometers per day during the study phase as compared with the entire 6.5-month period, this suggests the EE and water turnover determined in this paper are representative of the entire run. Both of the variables in question, if inadequate, are associated with serious health complications and impaired performance. With this information it will be possible for athletes, nutritionists, and coaches to optimize performance without compromising the health of the participant.

Address for correspondence: Associate Professor Peter S. W. Davies, Children’s Nutrition Research Centre Department of Paediatrics & Child Health, Royal Children’s Hospital, Herston, Queensland 4029, Australia; E-mail


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