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The aim of this study was to investigate whether VO(2)max can be accurately measured in a respiration chamber. Thirty participants aged 23.4 +/- 3.9 years with a wide range in VO(2)max were included. Participants performed four incremental cycle ergometer tests (VO(2)max) with a minimum of 5 days between tests. These tests consisted of one familiarization test with face mask, followed by two VO(2)max tests in the respiration chamber and one test with face mask in randomized order. Oxygen consumption and CO2 production were measured continuously using Omnical (Maastricht University, the Netherlands) gas analysis system. The mean VO(2)max was 3634 +/- 766 ml, which resulted in mean VO(2)max per lean body mass of 60.8 +/- 8.0 ml/kg. Repeated respiration chamber tests showed a high concordance, and no significant differences were detected between tests (Lin's concordance correlation coefficient (Rc) = 0.99; increment 70 +/- 302 ml/min; p = .38). There was high concordance between the mean VO(2)max from both respiration chamber tests and the mean face mask tests, and no significant difference (Rc = 0.99; increment 41 +/- 173 ml/min; p = .22) was observed. The Bland-Altman plots showed no proportional bias between different tests. In conclusion, the respiration chamber has been found to be a valid and reproducible method for measuring VO(2)max. New research opportunities are possible in the respiration chamber, such as maximal exercise testing during 24-hour measurements.

Objective Recent studies suggest that hypoxia exposure may improve glucose homeostasis, but well-controlled human studies are lacking. We hypothesized that mild intermittent hypoxia (MIH) exposure decreases tissue oxygen partial pressure (pO2) and induces metabolic improvements in people who are overweight/obese. Methods In a randomized, controlled, single-blind crossover study, 12 men who were overweight/obese were exposed to MIH (15 % O2, 3 × 2 h/day) or normoxia (21 % O2) for 7 consecutive days. Adipose tissue (AT) and skeletal muscle (SM) pO2, fasting/postprandial substrate metabolism, tissue-specific insulin sensitivity, SM oxidative capacity, and AT and SM gene/protein expression were determined. Furthermore, primary human myotubes and adipocytes were exposed to oxygen levels mimicking the hypoxic and normoxic AT and SM microenvironments. Results MIH decreased systemic oxygen saturation (92.0 ± 0.5 % vs 97.1 ± 0.3, p, Highlights • MIH exposure decreases oxygen partial pressure in human adipose tissue and skeletal muscle. • MIH exposure induces a shift in substrate utilization toward glycolytic metabolism. • Hypoxia exposure increases insulin-independent glucose uptake in primary human myotubes, at least in part through AMPK. • MIH does not alter adipose tissue, hepatic and peripheral insulin sensitivity.

Whole-room indirect calorimeters have been used to study human metabolism for more than a century. These studies have contributed substantial knowledge to the assessment of nutritional needs and the regulation of energy expenditure and substrate oxidation in humans. However, comparing results from studies conducted at different sites is challenging because of a lack of consistency in reporting technical performance, study design, and results. In May 2019, an expert panel was convened to consider minimal requirements for conducting and reporting the results of human whole-room indirect calorimeter studies. We propose Room Indirect Calorimetry Operating and Reporting Standards, version 1.0 (RICORS 1.0) to provide guidance to ensure consistency and facilitate meaningful comparisons of human energy metabolism studies across publications, laboratories, and clinical sites.

BackgroundSeveral indirect calorimetry (IC) instruments are commercially available, but comparative validity and reliability data are lacking. Existing data are limited by inconsistencies in protocols, subject characteristics, or single-instrument validation comparisons. The aim of this study was to compare accuracy and reliability of metabolic carts using methanol combustion as the cross-laboratory criterion.MethodsEight 20-minute methanol burn trials were completed on 12 metabolic carts. Respiratory exchange ratio (RER) and percent O-2 and CO2 recovery were calculated.ResultsFor accuracy, 1 Omnical, Cosmed Quark CPET (Cosmed), and both Parvos (Parvo Medics trueOne 2400) measured all 3 variables within 2% of the true value; both DeltaTracs and the Vmax Encore System (Vmax) showed similar accuracy in measuring 1 or 2, but not all, variables. For reliability, 8 instruments were shown to be reliable, with the 2 Omnicals ranking best (coefficient of variation [CV] ConclusionsOmnical, Parvo, Cosmed, and DeltaTrac had greater accuracy and reliability. The small number of instruments tested and expected differences in gas calibration variability limits the generalizability of conclusions. Finally, humidity and temperature could be modified in the laboratory to optimize IC conditions.

For over two centuries, scientists have measured gas exchange in animals and humans and linked this to energy expenditure of the body. The aim of this review is to provide a comprehensive overview of open-circuit diluted flow indirect calorimetry and to help researchers to make the optimal choice for a certain system and its application. A historical perspective shows that ‘open circuit diluted flow’ is a technique first used in the 19th century and applicable today for room calorimeters, ventilated hood systems, and facemasks. Room calorimeters are a classic example of an open-circuit diluted flow system. The broadly applied ventilated hood calorimeters follow the same principle and can be classified as a derivative of these room calorimeters. The basic principle is that the subject breathes freely in a passing airflow that is fully captured and analyzed. Oxygen and CO2 concentrations are measured in inlet ambient air and captured outlet air. The airflow, which is adapted depending on the application (e.g., rest versus exercise), is measured. For a room indirect calorimeter, the dilution in the large room volume is also taken into account, and this is the most complex application of this type of calorimeter. Validity of the systems can be tested by alcohol burns, gas infusions and by performing repeated measurements on subjects. Using the latter, the smallest CV (%) was found for repeated VO2max tests (1.2%) with an SD of approximately 1 kJ min−1. The smallest SD was found for sleeping metabolic rate (0.11 kJ min−1) with a CV (%) of 2.4%.

This study aimed to analyze the intra-individual variation in VO2max of human subjects using total-capture and free-flow indirect calorimetry. Twenty-seven men (27 +/- 5 year; VO2max 49-79 mL center dot kg(-1)center dot min(-1)) performed two maximal exertion tests (CPETs) on a cycle ergometer, separated by a 7 +/- 2 day interval. VO2 and VCO2 were assessed using an indirect calorimeter (Omnical) with total capture of exhalation in a free-flow airstream. Thirteen subjects performed a third maximal exertion test using a breath-by-breath calorimeter (Oxycon Pro). On-site validation was deemed a requirement. For the Omnical, the mean within-subject CV for VO2max was 1.2 +/- 0.9% (0.0%-4.4%) and for ergometer workload P (max) 1.3 +/- 1.3% (0%-4.6%). VO2max values with the Oxycon Pro were significantly lower in comparison with Omnical (P t test) with mean 3570 vs 4061 and difference SD 361 mL center dot min(-1). Validation results for the Omnical with methanol combustion were -0.05 +/- 0.70% (mean +/- SD; n = 31) at the 225 mL center dot min(-1) VO2 level and -0.23 +/- 0.80% (n = 31) at the 150 mL center dot min(-1) VCO2 level. Results using gas infusion were 0.04 +/- 0.75% (n = 34) and -0.99 +/- 1.05% (n = 24) over the respective 500-6000 mL center dot min(-1) VO2 and VCO2 ranges. Validation results for the Oxycon Pro in breath-by-breath mode were - 2.2 +/- 1.6% (n = 12) for VO2 and 5.7 +/- 3.3% (n = 12) for VCO2 over the 1000-4000 mL center dot min(-1) range. On a Visual analog scale, participants reported improved breathing using the free-flow indirect calorimetry (score 7.6 +/- 1.2 vs 5.1 +/- 2.7, P = 0.008). We conclude that total capturing free-flow indirect calorimetry is suitable for measuring VO2 even with the highest range. VO2max was linear with the incline in P (max) over the full range.

Human eating behavior may be influenced non-homeostatically by the rewarding value of foods, i.e. 'liking' (pleasure/palatability) and 'wanting' (incentive motivation). The objectives of this study were to validate a computer test for assessment of rewarding value of food, and to assess how rewarding value of food is affected by eating a dessert-specific (chocolate mousse, CM) vs. dessert non-specific, neutral food item (cottage cheese, CC). Seventy-three subjects (47f/26m, age 27.8+/-10.0 y, BMI 24.1+/-3.3 kg/m(2)), studied in a randomized cross-over design, came to the university twice, fasted. A computer test was developed to determine rewarding value, i.e. 'liking' and 'wanting', for 72 items divided in six categories (bread, filling, drinks, dessert, sweets, stationery). 'Liking' was measured by indicating relative preference of paired items (within/between categories), 'wanting' by working to earn items to choose from. Subjects completed the computer test before and after consumption of CM/CC, matched for energy content (5.6 kJ/g) and daily energy requirements (10%). 'Liking' and 'wanting' scores of all fasted subjects on the two test-days showed 62-73% reproducibility. CM was liked more than CC (p

to the editor: We read with much interest the invited review of Drs. Poole and Jones ([3][1]) in which they waived the concept of Vo2peak, and as far as we believe, based on fragile scientific arguments. Still, we believe Poole and Jones’ review is of interest to all those involved in exercise

High-fibre diets offer several beneficial health effects. The objective of the present study was to investigate whether replacement of 30 % of the available carbohydrates with polydextrose (PDX) or soluble maize fibre (SCF) at breakfast and lunch would result in an increased fat oxidation rate and satiety, which may be of relevance for body weight control and diabetes prevention. In a single-blind, randomised cross-over study, eighteen overweight men and women underwent four different dietary interventions, which consisted of a PDX diet, a SCF diet and two control diets (full energetic and isoenergetic, comparable with PDX with respect to g or energy percentage of macronutrients, respectively). Glycaemic profile, energy expenditure and substrate oxidation were measured for 24 h in a respiration chamber. Circulating insulin, NEFA and TAG concentrations were determined over a 14 h period during daytime. Appetite ratings were assessed using visual analogue scales. The replacement of available carbohydrates with PDX or SCF reduced the peak glucose response, which was accompanied by reduced postprandial insulin responses. Moreover, higher concentrations of circulating NEFA were observed after consumption of both fibre diets, which were accompanied by an increased fat oxidation over 24 h. This effect was mainly attributed to the lower energetic value of the fibre diets and not to the fibresper se. Besides increasing fat oxidation, PDX exerted a pronounced suppressive effect on appetite ratings. The replacement of available carbohydrates with PDX may be of special interest because of its beneficial effects on metabolic profile and it may affect body weight control in the long term.

Background: Sleep has been associated with the regulation of energy balance, yet the relation between sleep stages and energy expenditure remains unclear.Objective: The objective was to investigate the relation between sleep stages and energy expenditure, with sleep stage and overnight energy expenditure patterns taken into account.Design: Thirteen subjects aged (mean +/- SD) 24.3 +/- 2.5 y with a BMI (in kg/m(2)) of 23.6 +/- 1.7 slept in a respiration chamber while sleep was polysomnographically recorded to determine wake after sleep onset (WASO), slow-wave sleep (SWS), and rapid eye movement (REM) sleep. Energy expenditure was calculated during each sleep stage for the whole night and separately for sleeping metabolic rate (SMR; ie, 3-h period during the night with the lowest mean energy expenditure) and non-SMR.Results: Energy expenditure and sleep stages showed characteristic patterns during the night, independently of each other. Sleep stages exerted no effect on energy expenditure during the whole night, except for WASO compared with SWS (P Conclusions: Energy expenditure does not vary according to sleep stage overnight, except for higher energy expenditure during wake episodes than during SWS and REM sleep. Coincidence of the sleep stage pattern and the overnight energy expenditure pattern may have caused accidental relations in previous observations. This trial was registered at http://apps.who.int/trialsearch as NTR2926.

Body mass, body composition and sleeping metabolic rate before, during and after endurance training.Westerterp KR, Meijer GA, Schoffelen P, Janssen EM.Department of Human Biology, University of Limburg, Maastricht, The Netherlands.Metabolic rate, more specifically resting metabolic rate (RMR) or sleeping metabolic rate (SMR), of an adult subject is usually expressed as a function of the fat-free mass (FFM). Chronic exercise is thought to increase FFM and thus to increase RMR and SMR. We determined body mass (BM), body composition, and SMR before, during, and after an endurance training programme without interfering with energy intake. The subjects were 11 women and 12 men, aged 37 (SD 3) years and body mass index 22.3 (SD 1.5) kg.m-2. The endurance training prepared subjects to run a half marathon competition after 44 weeks. The SMR was measured overnight in a respiration chamber. Body composition was measured by hydrostatic weighing. Measurements were performed at 0, 8, 20, 40, and 90 weeks after the start of the training. The BM had decreased from a mean value of 66.6 (SD 6.9) to 65.6 (SD 6.7) kg (P < 0.01), fat mass (FM) had decreased from 17.1 (SD 3.9) to 13.5 (SD 3.6) kg (P < 0.001), and FFM had increased from 49.5 (SD 7.3) to 52.2 (SD 7.6) kg (P < 0.001) at 40 weeks. Mean SMR before and after 40 weeks training was 6.5 (SD 0.7) and 6.2 (SD 0.6) MJ.day-1 (P < 0.05). The decrease in SMR was related to the decrease in BM (r = 0.62, P = 0.001). At 90 weeks, when most subjects had not trained for nearly a year, BM and SMR were not significantly different from the initial value while FM and FFM had not changed since week 40 of training

Eating behavior can be influenced by the rewarding value of food, i.e., "liking" and "wanting." The objective of this study was to assess in normal-weight dietary restrained (NR) vs. unrestrained (NU) eaters how rewarding value of food is affected by satiety, and by eating a nonhealthy perceived, dessert-specific food vs. a healthy perceived, neutral food (chocolate mousse vs. cottage cheese). Subjects (24NR age = 25.0 +/- 8.2 years, BMI = 22.3 +/- 2.1 kg/m(2); 26NU age = 24.8 +/- 8.0 years, BMI = 22.1 +/- 1.7 kg/m(2)) came to the university twice, fasted (randomized crossover design). Per test-session "liking" and "wanting" for 72 items divided in six categories (bread, filling, drinks, dessert, sweets, stationery (placebo)) was measured, before and after consumption of chocolate mousse/cottage cheese, matched for energy content (5.6 kJ/g) and individual daily energy requirements (10%). Chocolate mousse was liked more than cottage cheese (P < 0.05). After consumption of chocolate mousse or cottage cheese, appetite and "liking" vs. placebo were decreased in NR and NU (P < 0.03), whereas "wanting" was only decreased in NR vs. NU (P

There is a growing tendency to estimate energy requirements by means of the assessment of resting energy expenditure (REE) by indirect calorimetry. In this study a computerized open-circuit ventilated hood system is described that was constructed for assessing REE in a clinical setting. Measurement error of the device, tested by ethanol combustion was +2% for VO2 and VCO2 and less than 1% for respiratory quotient. To assess the within-patient variability of REE measurements performed in a daily clinical routine, we studied the following aspects of the measurements in several groups of patients with chronic obstructive pulmonary disease: (1) reproducibility, (2) the influence of routine physical activities before the measurement, (3) measurement duration, and (4) difference between measurements using a ventilated hood or a mouthpiece. Reproducibility of measurements with a 2-month interval in 12 weight-stable patients was good (1415 +/- 128 and 1398 +/- 138 kcal/day). Variations due to limited activities and different measurement durations (between 10 and 30 minutes) were not significant. Variations between measurements with a mouthpiece and ventilated hood were larger in patients than in healthy control subjects, but for both groups no systematic difference was established. REE can be assessed reliably by short-term measurements with a ventilated hood in stable chronic obstructive pulmonary disease patients on an outpatient basis, provided a short rest is taken before the measurement.

Background/Objectives:In South Africa (SA), the prevalence of obesity in women is 56%, with black women being most at risk (62%). Studies in the United States have demonstrated ethnic differences in resting (REE) and total daily energy expenditure (TDEE) between African American (AA) and their white counterparts. We investigated whether differences in EE exist in black and white SA women, explaining, in part, the ethnic obesity prevalence differences.Subjects/Methods:We measured REE, TDEE and physical activity EE (PAEE) in lean (BMI 30 kg m(-2)) SA women (N=44, 30+/-6 year). REE, TDEE, PAEE and total awake EE were measured during a 21 h stay in a respiration chamber.Results:Black and white subjects within obese and lean groups were not significantly different for age, mass, BMI and % body fat. However, fat-free mass (kg FFM) was consistently lower in the black women (P

After 4 weeks of dieting, 4 weeks of frequent exercise training (6h/wk) were added to a low energy diet of 3.0 MJ/day in 6 out of 12 healthy obese female subjects (aged 30–46 years) in order to compare changes in sleeping metabolic rate (SMR) and glucose induced thermogenesis (GIT). On the basis of BMI and percentage of body fat a diet group (D) and a diet-exercise group were formed (DE). SMR and GIT were both measured during a 36-h stay in a respiration chamber. Weight loss and changes in body composition were similar after 4 weeks of dieting. Adding 4 weeks of physical training for the DE group after 4 weeks of dieting did not result in significant differences between D and DE. SMR decreased significantly after 4 weeks of dieting (D 13%; DE 12%, P

The shape of the cumulative food intake curve of normal weight and obese women was studied during solid food lunches, artificially prolonged meals, and energetically enriched meals eaten in a laboratory setting. Subjects (86 normal weight, 50 obese) displayed consistent eating behaviour over 3–6 repeated meals, with marked differences between individuals. Aspects of eating behaviour were reflected in decelerated and nondecelerated (or linear) cumulative intake curves depending on changes or no changes in eating rate during the course of a meal, respectively. A change in eating rate was generally related to a decrease in bite size, with bite rate remaining constant, from the third temporal quarter of the meal onwards, resulting in a decelerated cumulative intake curve. The nondecelerated (linear) cumulative intake curve does not show this change in eating rate: in the first three temporal quarters bite size and bite rate were constant, whereas in the fourth temporal quarter bite size decreased slightly, compensated by a small increase in bite rate. Intraindividual ranges for meal parameters such as chewing time per bite, bite interval and initial eating rate indicated consistency of individual eating behaviour. In manipulation experiments with a subset of 21 subjects in which meals were artificially prolonged by an interval of 8 min, the cumulative intake curves did not differ significantly from the original cumulative intake curves in 10 nondecelerated (linear) eaters, but showed a change towards nondecelerated curves in 8 out of 11 decelerated eaters. In manipulation experiments with a subset of 34 subjects, who consumed similar meals, but energetically enriched by addition of either fat, protein, or carbohydrates, 25 of these subjects showed no change in the shape of their cumulative intake curves.

The largest component of daily energy expenditure is resting energy expenditure as reflected in overnight metabolic rate (OMR) and sleeping metabolic rate (SMR). Here, we determined the variation in OMR (24:00-6:00 h) and SMR values (3 h intervals) as affected by physical activity (PA) during the day and the night. Subjects were 32 females and 17 males, age 18-52 years. Energy expenditure (EE) was measured for 36 h in a whole room calorimeter (14 m3), starting in the evening, providing values before and after behavioral limitation. The mean intra-individual coefficient of variation was 1.8+/-1.4% for SMRmin (minimum EE), 2.8+/-2.0% for SMRact (minimum PA), 2.4+/-2.5% for SMRres (minimum residual EE, residual calculated from 24 h relationship between EE and PA) and 2.8+/-2.2% for OMR (n=49). Mean clock time for SMR ranged from 3:15 till 4:13 h. EE and PA increased in the hour before awakening. Surprisingly, OMR showed a significant 2.7% increase (P

CLAESSENS-VAN OOIJEN, ANNE M.J., KLAAS R. WESTERTERP, LOEK WOUTERS, PAUL F.M. SCHOFFELEN, ANTON A. VAN STEENHOVEN, AND WOUTER D. VAN MARKEN LICHTENBELT. Heat production and body temperature during cooling and rewarming in overweight and lean men. Obesity. 2006;14: 1914‐1920. Objective: To compare overweight and lean subjects with respect to thermogenesis and physiological insulation in response to mild cold and rewarming. Research Methods and Procedures: Ten overweight men (mean BMI, 29.2 ! 2.8 kg/m 2 ) and 10 lean men (mean BMI, 21.1 ! 2.0 kg/m 2 ) were exposed to cold air for 1 hour, followed by 1 hour of rewarming. Body composition was determined by hydrodensitometry and deuterium dilution. Heat production and body temperatures were measured continuously by indirect calorimetry and thermistors, respectively. Muscle activity was recorded using electromyography. Results: In both groups, heat production increased significantly during cooling (lean, p " 0.004; overweight, p " 0.006). The increase was larger in the lean group compared with the overweight group (p " 0.04). During rewarming, heat production returned to baseline in the overweight group and stayed higher compared with baseline in the lean group (p " 0.003). The difference in heat production between rewarming and baseline was larger in the lean (p " 0.01) than in the overweight subjects. Weighted body temperature of both groups decreased during cold exposure (lean, p " 0.002; overweight, p # 0.001) and did not return to baseline during rewarming. Discussion: Overweight subjects showed a blunted mild cold-induced thermogenesis. The insulative cold response was not different among the groups. The energy-efficient response of the overweight subjects can have consequences for energy balance in the long term. The results support the concept of a dynamic heat regulation model instead of temperature regulation around a fixed set point.

Intra-individual variation of basal metabolic rate and the influence of daily habitual physical activity before testing.Adriaens MP, Schoffelen PF, Westerterp KR.Department of Human Biology, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands. M.adriaens@HB.Unimaas.nlThe present study determined the intra-individual variation of BMR measurements, using a standard out-patient protocol, with the subjects transporting themselves to the laboratory for the BMR measurements after spending the night at home. The effect of a non-fasting state and variation in daily habitual physical activity the day before testing was evaluated. Eight male and eleven female subjects participated in three BMR measurements with 2-week intervals. Physical activity was estimated with a tri-axial accelerometer for movement registration, during the 3 d before each BMR measurement. There were no significant differences in estimated BMR (ANOVA repeated measures, P=0.88) and in physical activity (ANOVA repeated measures, P=0.21). Mean within-subject CV in BMR was found to be 3.3 (SD 2.1) %, ranging from 0.4 to 7.2 %. Differences between BMR measurements could not be explained by differences in physical activity the day before; however the mean within-subject CV in BMR changed from 5.7 to 5.2 % after correcting for within-machine variability and from 5.2 to 3.3 % after excluding five measurements because of non-compliance to the protocol including fasting. In conclusion, BMR values measured with a standard out-patient protocol are sufficiently reproducible for most practical purposes despite the within-subject variability in physical activity the day before the measurement. For this purpose, however, non-fasting subjects must be excluded and a regular function check of the ventilated-hood system is recommendable

Introduction Hypocretin deficiency causes narcolepsy, a condition characterized by excessive daytime sleepiness, cataplexy, and fragmented nocturnal sleep. Co-morbid overweight is present in two thirds of narcolepsy patients. Moreover one third of them is obese. Why narcolepsy patients gain weight is not known. They do not seem to eat and/or sleep more during 24 h than controls. This study was performed to detect a possible decrease in energy expenditure that could be the cause for the overweight in narcolepsy. This is the first study using a respiration chamber to measure Energy Expenditure in narcolepsy. Materials and methods Nine hypocretin deficient male patients with narcolepsy-cataplexy, and nine sex, age and body mass index (BMI) matched controls were enrolled. Energy Expenditure was measured for 24 h in a respiration chamber. Spontaneous physical activity was measured by a radar system based on Doppler principle. Subjects were given a diet to maintain energy balance based on the Harris–Benedict equation. Total Energy Expenditure (TEE), Overnight Metabolic Rate (OMR) and lowest Sleeping Metabolic Rate (SMRmin) were calculated. In addition, measured SMR was compared with SMR calculated with a prediction equation based on body composition. Results Narcolepsy patients did not differ from controls in BMI (27.4 ± 3.9 vs. 27.5 ± 4.2; P = 9.4) or age (38.1 ± 16.0 vs. 36.8 ± 15.2; P = .86) respectively. There were no differences in TEE (10.6 ± 1.2 vs. 10.6 ± .80 MJ/d; P = .99) OMR (5.7 ± .73 vs. 6.0 ± .55 MJ/d; P = .35), SMRmin (5.4 ± .76 vs. 5.4 ± .51 MJ/d; P = .99) and spontaneous activity between narcolepsy patients and matched controls (2862 ± 514 vs. 2732 ± 245 counts/d; P = .50). For both groups, measured SMR was closely related to SMR predicted from body composition. Conclusion Energy expenditure in narcolepsy patients is similar to matched controls. It is conceivable that we were not close enough to onset of the disease, when patients usually gain weight, to detect a possible difference before a new metabolic set point establishes. Acknowledgement This study was supported by a grant from UCB Pharma.

Schoffelen, Paul F. M., Klaas R. Westerterp, Wim H. M. Saris, and Foppe Ten Hoor. A dual-respiration chamber system with automated calibration. J. Appl. Physiol. 83(6): 2064–2072, 1997.—This study characterizes respiration chambers with fully automated calibration. The system consists of two 14-m3pull-type chambers. Care was taken to provide a friendly environment for the subjects, with the possibility of social contact during the experiment. Gas analysis was automated to correct for analyzer drift and barometric pressure variations and to provide ease of use. Methods used for checking the system’s performance are described. The gas-analysis repeatability was within 0.002%. Results of alcohol combustion (50–350 ml/min CO2) show an accuracy of 0.5 ± 2.0 (SD) % for O2consumption and −0.3 ± 1.6% for CO2 production for 2- to 24-h experiments. It is concluded that response time is not the main factor with respect to the smallest practical measurement interval (duration); volume, mixing, gas-analysis accuracy, and levels of O2 consumption and CO2 production are at least equally important. The smallest practical interval was 15–25 min, as also found with most chamber systems described in the literature. We chose to standardize 0.5 h as the minimum measurement interval.

Experiments were designed to test the traditional assumption that during level walking all of the energy from oxidation of fuel appears as heat and no work is done. Work is force expressed through distance, or energy transferred from a man to the environment, but not as heat. While wearing a suit calorimeter in a respiration chamber, five women and five men walked for 70 to 90 min on a level treadmill at 2.5, 4.6, and 6.7 km.h-1 and pedalled a cycle ergometer for 70 to 90 min against 53 and 92 W loads. They also walked with a weighted backpack and against a horizontal load. During cycling, energy from fuel matched heat loss plus the power measured by the ergometer. During walking, however, energy from fuel exceeded that which appeared as heat, meaning that work was done. The power increased with walking speed; values were 14, 29, and 63 W, which represented 11, 12, and 13% of the incremental cost of fuel above the resting level. Vertical and horizontal loads increased the fuel cost and heat loss of walking but did not alter the power output. This work energy did not re-appear as thermal energy during 18 h of recovery. The most likely explanation of the work done is in the inter-action between the foot and the ground, such as compressing the heel of the shoe and bending the sole. We conclude that work is done in level walking.