Estimating energy expenditure for brief bouts of exercise with acute ...

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Estimating energy expenditure for brief bouts of exercise with acute recovery Christopher B. Scott

Abstract: Four indirect estimations of energy expenditure were examined, (i) O2 debt, (ii) O2 deficit, (iii) blood lactate concentration, and (iv) excess CO2 production during and after 6 exercise durations (2, 4, 10, 15, 30, and 75 s) performed at 3 different intensities (50%, 100%, and 200% of VO2 max). Analysis of variance (ANOVA) was used to determine if significant differences existed among these 4 estimations of anaerobic energy expenditure and among 4 estimations of total energy expenditure (that included exercise O2 uptake and excess post-exercise oxygen consumption, or EPOC, measurements). The data indicate that estimations of anaerobic energy expenditure often differed for brief (2, 4, and 10 s) bouts of exercise, but this did not extend to total energy expenditure. At the higher exercise intensities with the longest durations O2 deficit, blood lactate concentration, and excess CO2 estimates of anaerobic and total energy expenditure revealed high variability; however, they were not statistically different. Moreover, they all differed significantly from the O2 debt interpretation (p < 0.05). It is concluded that as the contribution of rapid substrate-level ATP turnover with lactate production becomes larger, the greatest error in quantifying total energy expenditure is suggested to occur not with the method of estimation, but with the omission of a reasonable estimate of anaerobic energy expenditure. Key words: O2 deficit, lactate, O2 debt, EPOC, anaerobic energy expenditure. Résumé : Nous analysons quatre mesures indirectes de la dépense d’énergie en anaérobiose : la dette d’oxygène, le déficit d’oxygène, la production de lactate et le surplus de production du CO2 pendant et à la suite de 6 exercices de durée différente (2, 4, 10, 15, 30 et 75 s) et d’intensité variée (50 %, 100 %, 200 % du VO2 max). On utilise une analyse de variance pour tester statistiquement les différences entre les quatre mesures indirectes de la dépense d’énergie en anaérobiose et les quatre mesures indirectes de la dépense d’énergie totale obtenues par l’analyse de la consommation d’oxygène durant l’effort et de celle au-dessus des valeurs de repos durant la récupération. D’après ces observations, l’estimation de la dépense d’énergie anaérobie varie d’une brève période d’effort à l’autre (2, 4 et 10 s) mais ne se répercute pas sur la dépense énergétique totale. Au cours des efforts d’intensité plus élevée et de durée plus longue, les mesures indirectes de la dépense d’énergie anaérobie et de la dépense énergétique totale obtenues par l’analyse du déficit d’oxygène, de la production de lactate et du surplus de production du CO2 présentent une variation importante mais ne sont pas statistiquement différentes. Par contre, ces dernières mesures diffèrent significativement (p < 0,05) de celles obtenues par l’analyse de la dette d’oxygène. En conclusion, au fur et à mesure que s’accroît le renouvellement de l’ATP des substrats dits rapides et associés à la production de lactate, on commet plus d’erreurs dans la détermination de la dépense d’énergie totale : la mise à l’écart d’une bonne proportion de la dépense d’énergie en anaérobiose en est responsable et non pas la méthode. Mots clés : déficit d’oxygène, lactate, dette d’oxygène, EPOC, dépense d’énergie anaérobie. [Traduit par la Rédaction]

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Introduction Biological energy expenditure results from energy transfer and consists of heat and entropy production. Entropy can not be directly measured, therefore heat production has served as the standard means of interpreting both efficiency and energy expenditure. Exercise energy expenditure results from ATP turnover; that is, energy transfer during the hydrolysis of ATP to fuel muscular work (i.e., chemo-mechanical conReceived 24 February 2005. Accepted 29 June 2005. Published on the NRC Research Press Web site at http://apnm.nrc.ca on 7 March 2006. C.B. Scott. Department of Sports Medicine, University of Southern Maine, 37 College Ave., Gorham, ME 04038, USA (e-mail: [email protected]). Appl. Physiol. Nutr. Metab. 31: 144–149 (2006)

version) and the metabolic re-synthesis of ATP (e.g., conversion of glucose to ATP). Because of the inherent difficulties in measuring heat loss, O2 uptake remains the most popular method to estimate heat production and, by inference, energy expenditure. It is important to keep in mind, however, that although O2 uptake provides an excellent representation of aerobic ATP turnover, it does not represent the heat produced by rapid anaerobic glycolytic ATP turnover (i.e., an accelerated substrate-level phosphorylation resulting in lactate production that exceeds O2 uptake) (Gnaiger and Kemp 1990; Scott and Kemp 2005). The quantification of total energy expenditure for exercise and recovery includes the measurement of exercise O2 uptake and excess post-exercise O2 consumption (EPOC) along with anaerobic glycolytic ATP turnover. Unfortunately, validity problems exist for all direct measures and indirect

doi:10.1139/H05-013

© 2006 NRC Canada

Scott

estimations of anaerobic ATP turnover. For example, lactate measurements are problematic for many reasons, one of which is that lactate concentrations are different at various sampling sites, such that muscle lactate concentrations (a direct measure) are different from blood lactate concentrations (an indirect estimate) (Karlsson 1971; Medbo 1993; Tesch et al. 1982). The use of the O2 deficit as an indirect estimate of anaerobic ATP turnover also has several drawbacks that include questionable assumptions of mechanical and metabolic efficiency (Graham 1996; Krustrup et al. 2003; Pahud et al. 1980). The problems inherent to anaerobic measurements tend to discourage their use in the estimation of total energy expenditure even though studies have clearly revealed that anaerobic contribution to brief and intense exercise (Greenhaff and Timmons 1998; Shulman and Rothman 2001; Spriet 1995) and recovery (Baker and Gleeson 1998) can be significant. There are, however, several published methods that have been used to estimate anaerobic energy expenditure. This raises the question as to whether the absence of an anaerobic energy expenditure measurement has a significant influence on the interpretation of total energy expenditure. With this in mind, 4 indirect estimates of anaerobic energy expenditure were used to determine their potential in estimating total energy expenditure. It was hypothesized that measurements focusing solely on O2 uptake (e.g., exercise O2 uptake and O2 debt) misrepresent total energy expenditure because they omit rapid anaerobic glycolytic ATP turnover from the interpretation.

Materials and methods Subjects The study protocol was approved by the University of Southern Maine’s Institutional Review Board. Informed consent was obtained from 9 physically active subjects (26 ± 7 years; 176 ± 9 cm; 79 ± 19 kg; VO2 max = 50.3 ± 5.2 mL·(kg·min)–1; 4 females, 5 males) prior to data collection. Metabolic data collection Oxygen uptake was measured via a commercially available metabolic cart (MMS-2400, Parvomedics; Sandy, UT). Gas exchange and volume were carefully calibrated before all tests. Work was performed on a Trackmaster treadmill (Carrollton, Tex.). Blood lactate concentration (Accusport, Mannheim, Germany) was obtained before each test and at 2 and 4 min into the seated recovery. The difference between resting blood lactate and the peak post-exercise blood lactate was taken as blood lactate concentration and converted into an energy expenditure measurement as 3 mL O2·(kg body mass·mmol blood lactate)–1 (1 L O2 = 20.9 kJ) (di Prampero and Ferretti 1999). Each subject reported to the laboratory at least 3 h after eating a meal. Preliminary exercise testing Aerobic capacity was determined using a standard Bruce treadmill protocol. Over the course of 3 separate days, subjects randomly completed 10 submaximal walks 10 min in duration at a 20% gradient and at a speed of 0.45 m·s–1 and a workload that elicited a respiratory exchange ratio (RER) of less than 0.99. The last 3 min of each walk was averaged as steady state energy expenditure for that particular work-

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load. These preliminary submaximal tests were used to create a regression for each subject that enabled the estimation of exercise energy expenditure and the O2 deficit for a brief bout of exercise at a workload of 200% of VO2 max (Buck and McNaughton 1999; Medbo et al. 1988). Exercise testing Work rates for the brief non-exhaustive exercise tests were set at 50%, 100%, and 200% of VO2 max. Exercise durations were 2, 4, 10, 15, 30, and 75 s. The order of each test was randomized and each was completed on separate days. With the treadmill on a gradient of 20%, 50% VO2 max represented a slow walk, 100% VO2 max was a brisk walk, and 200% VO2 max was a sprint. All exercise tests began with subjects at rest, standing and straddling the moving treadmill belt. Resting standing O2 uptake was slated for 2 min with actual data collection averaging 141 ± 18 s. Standing resting values averaged 5.1 ± 0.3 mL·(kg·min)–1 for all tests. Once the brief exercise bout was completed, subjects were immediately seated until energy expenditure fell below that subject’s previously recorded resting standing VO2 value. Resting standing VO2 was subtracted from all exercise and EPOC measurements. Energy expenditure estimations The O2 deficit at the onset of exercise is the period during which ATP and phosphocreatine (PC) stores are used. The resynthesis of the ATP and (or) PC stores occurs when exercise has ended, as part of EPOC. The O2 deficit and EPOC are therefore each responsible for one part of stored highenergy phosphate (ATP and (or) PC) turnover. In this regard, the respective partitioning of the O2 deficit and EPOC into ATP hydrolysis and ATP resynthesis is problematic, but must be accounted for (Pahud et al. 1980). Thus, for the measurement of total energy expenditure either the O2 deficit or EPOC, but not both, can represent the hydrolysis and resynthesis of the ATP and PC stores. The further partitioning of anaerobic ATP turnover into the components of stored ATP and PC hydrolysis and rapid substrate phosphorylation with lactate production represents another area of concern. The indirect methods described below attempt to recognize and account for this partitioning. Moreover, the recovery from exercise is mostly fueled by lactate and fatty acid oxidation; as such, it does not contain an anaerobic substratelevel phosphorylation component (Bahr 1992; Scott and Kemp 2005). Thus, for all total energy expenditure interpretations except O2 debt methodology, EPOC is calculated as 1 LO2 = 19.6 kJ in an attempt to dismiss rapid substratelevel ATP turnover from the recovery energy expenditure (a 20.9 kJ conversion contains glycolytic substrate-level phosphorylation as part of aerobic ATP turnover; that is, 2 of ~36 aerobically formed ATP occur via anaerobic substratelevel phosphorylation, a ~6% difference—the percent difference of 19.6 and 20.9 kJ is also ~6% (Scott and Kemp 2005)). The following 4 separate estimations of anaerobic and total energy expenditure were compared. (i) Traditional O2 debt methodology states that total energy expenditure can be interpreted solely via an O2 uptake measurement that includes exercise O2 uptake and the O2 debt as 1 L O2 = 20.9 kJ. An estimate of anaerobic energy expenditure using O2 uptake-only measurements required a © 2006 NRC Canada

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Table 1. Estimations of anaerobic energy expenditure. (A) 50% VO2 max (0.8 ± 0.1 m@s–1) Estimated anaerobic energy expenditure (kJ) based on Exercise duration (s)

O2 deficit

blood lactate concentration

excess CO2

O2 debt

2 4 10 15 30 75

1.3±0.4 2.7±0.7a 6.7±2.0acd 8.4±2.8ad 16.2±4.1ad 29.0±7.3acd

3.2±2.8 5.4±7.2 2.4±1.2b 3.1±1.5 12.2±8.5 8.3±5.2b

1.0±0.6 1.6±1.3b 1.8±0.6b 2.0±0.5b 2.8±0.5b 3.7±0.9b

1.3±0.8 2.0±1.7 2.4±0.8b 2.7±0.7b 3.8±0.6b 4.9±1.2b

excess CO2

O2 debt

1.4±0.6 2.3±0.9b 4.1±1.5b 4.1±0.7b 8.3±2.5b 40.0±11.1d

1.9±0.7 2.9±1.1 5.3±1.9b 5.3±1.0b 9.2±1.0bc 13.4±3.2ab

excess CO2

O2 debt

(B) 100% VO2 max (1.8 ± 0.3 m@s–1) Estimated anaerobic energy expenditure (kJ) based on Exercise duration (s) 2 4 10 15 30 75

O2 deficit 2.7±0.7 5.7±1.8a 14.9±5.5ad 17.4±5.3ac 29.3±11.3ad 51.3±19.5d

blood lactate concentration 2.5±1.7 5.0±3.2 6.1±2.2 5.2±1.1b 18.2±5.8 34.5±7.9

(C) 200% VO2 max (3.7 ± 0.6 m@s–1) Estimated anaerobic energy expenditure (kJ) based on Exercise duration (s) 2 4 10 15 30

O2 deficit ad

6.3±1.2 12.0±2.9ad 29.6±7.2ad 35.0±11.7d 78.7±18.8d

blood lactate concentration 6.1±3.8ad 7.6±4.1 25.5±16.3d 22.3±10.0 57.6±16.9d

bc

2.5±0.8 3.7±1.2b 17.5±10.0b 24.2±7.7 101.5±25.2d

3.2±1.1bc 4.5±1.1b 10.0±2.5bc 10.2±1.8b 18.9±1.6abc

Note: Anaerobic energy expenditure includes an estimate of rapid substrate-level ATP turnover and ATP and PC hydrolysis for each separate interpretation; these interpretations attempt to exclude aerobic ATP resynthesis (see Materials and methods). Values are means ± SD. a Significantly different from the estimate using CO2; ANOVA, p < 0.05. b Significantly different from the estimate using O2 deficit; ANOVA, p < 0.05. c Significantly different from the estimate using blood lactate; ANOVA, p < 0.05. d Significantly different from the estimate using O2 debt; ANOVA, p < 0.05.

means of determining and summing the two anaerobic components. An estimate of the ATP and PC component to anaerobic energy expenditure was taken as 20% of EPOC (Bangsbo et al. 1990). Anaerobic substrate level ATP turnover was calculated as the difference between EPOC conversion factors using 1 L O2 = 20.9 kJ and 1 L O2 = 19.6 kJ. (ii) O2 deficit represents both components of anaerobic energy expenditure with the conversion of 1 L O2 = 20.9 kJ. Oxygen deficits were calculated as the difference between real-time O2 uptake measurements and measured VO2 at 50% and 100% of VO2 max and estimated VO2 at 200% of VO2 max (see Preliminary Exercise Testing above). Total energy expenditure was calculated by adding the O2 deficit to exercise O2 uptake (1 L O2 = 20.9 kJ) and a modified EPOC calculated as 80% of the total EPOC so that the ATP and PC stores were represented by O2 deficit and not by EPOC. (iii) Rapid anaerobic glycolytic ATP turnover was estimated from blood lactate measures (see Metabolic Data Collection above). Anaerobic energy expenditure included this

glycolytic component plus 20% of the EPOC as an estimate of ATP and PC stores. Total energy expenditure consisted of blood lactate added to exercise O2 uptake (1 L O2 = 20.9 kJ) and EPOC measurements (1 L O2 = 19.6 kJ). (iv) “Excess” CO2 production results from the buffering of H+ during rapid glycolytic ATP turnover (as well as from hyperventilation; see legend of Fig. 3) and was identified whenever the RER of exercise and (or) EPOC exceeded 1.00. This methodology has not been validated (although CO2 can be used to estimate energy expenditure (Blaxter 1989; Kleiber 1975)). Excess CO2 was recorded until O2 uptake fell below a subject’s standing resting value. The difference between O2 (L·min–1) and CO2 (L·min–1) was converted to kJ (1 L CO2 = 20.9 kJ) to estimate rapid glycolysis with lactate production and then added to 20% of EPOC as a representation of the ATP and PC stores to estimate anaerobic energy expenditure. Excess CO2 production was added to exercise O2 uptake (1 L O2 = 20.9 kJ) and EPOC (1 L O2 = 19.6 kJ) to estimate total energy expenditure. © 2006 NRC Canada

Scott

Data analyses The 4 different estimations of anaerobic energy expenditure were compared for each intensity and duration using a standard analysis of variance (ANOVA). Estimations of total energy expenditure were compared with duration and intensity using 2-way ANOVA; both intensity and duration were examined using a 2-way ANOVA with repeated measures. A Tukey post-hoc test was used. The alpha level was set at p < 0.05. Values are reported as mean ± standard deviation (SD).

147 Fig. 1. The figure represents 4 estimations of total energy expenditure for submaximal exercise. Resting O2 uptake was subtracted from all exercise and EPOC data. Data for 2, 4, and 10 s time periods are not different among estimations. Significant differences are evident at 15 s: #, O2 deficit estimation is different from excess CO2 estimates; *, O2 deficit estimation is different from all other interpretations (p < 0.05).

Results The protocol followed was brief, non-exhaustive exercise, followed by acute recovery. Subjects could easily finish all but one of the assigned exercise bouts; none of the subjects could complete a 75 s run at 200% of VO2 max, therefore these data are not provided. Estimations of anaerobic energy expenditure revealed a high variability (Table 1). With the exception of the lowest intensity (50% VO2 max) and most brief exercise (2 and 4 s runs), the O2 deficit provided the largest estimate of anaerobic energy expenditure, which was statistically greater in comparison to excess CO2 production and the O2 debt (ANOVA; p < 0.05) (Table 1). Estimates of anaerobic energy expenditure using blood lactate differed significantly from that estimated by O2 debt only when coupled with the highest exercise intensity (200% VO2 max) and longest duration (30 s; p < 0.05). Estimates using excess CO2 production were significantly greater than those using O2 debt at the higher exercise intensities (100% and 200% VO2 max) when coupled to the longest duration (p < 0.05) (Table 1). Two-way ANOVA with repeated measures indicated that both exercise intensity and duration had a significant effect on total energy expenditure (p < 0.001) and that an interaction between the two existed (p < 0.001). Within exercise intensity, the method of estimation had a significant effect on total energy expenditure (2-way ANOVA; p < 0.001). Likewise, within exercise duration, intensity had a significant effect on total energy expenditure (2-way ANOVA; p < 0.003). Post-hoc testing revealed significant differences among the estimations of total energy expenditure only during 15 s or more of exercise, where the estimate that included O2 deficit was often the largest (see Figs. 1, 2, and 3). For the 75 s bout of exercise at 100% VO2 max and the 30 s bout at 200% VO2 max, the estimation based on O2 debt was significantly lower than the other estimations of total energy expenditure (p < 0.05).

Discussion Four indirect estimations of total energy expenditure for a brief treadmill exercise with acute recovery were compared. It was found that (i) all indirect estimations of total energy expenditure were similar at the briefest workloads from 50%–200% VO2 max and (ii) at the higher exercise intensities with the longest durations O2 deficit, blood lactate concentration, and CO2 estimations of total energy expenditure were significantly greater than the estimation based on O2 debt. This study has obvious limitations, the most important of which is the lack of a “gold standard” measure of anaerobic energy expenditure. Moreover, our methods assume equivalent efficiency among anaerobic- and aerobic-supported ATP

turnover that may not be true (Krustrup et al. 2003). Because this was not a validation study, inferences regarding the accuracy of each indirect interpretation cannot be made; this is well understood. However, it was not the intent of this investigation to determine the extent of error that certainly exists within each individual estimate of anaerobic energy expenditure. Instead, the aim was to examine the potential for misinterpretation of total energy expenditure when it does not include a reasonable estimate of anaerobic energy expenditure. This appears especially warranted with brief heavy to severe exercise where anaerobic and recovery energy expenditure contributions are relatively large. Unfortunately, many scientists still do not use an estimate of anaerobic energy expenditure or a measure of EPOC when attempting to quantify total energy expenditure even though both can be significant (Scott 1997). For example, in a review of comparative exercise physiology (Gleeson and Hancock 2002), it was suggested that the cost of sprinting requires 3 energy expenditure measures—exercise O2 uptake, EPOC, and lactate—yet previous studies by these authors never included lactate as part of the cost of activity (Baker and Gleeson 1998, 1999; Nedrow et al. 2001). The range of the estimates of anaerobic energy expenditure during the 2, 4, and 10 s exercise periods within each of the 3 intensities underscores the well-known validity problems associated with estimating anaerobic ATP turnover (Table 1). Even so, estimates of total energy expenditure within the 3 intensities for 2, 4, and 10 s of non-exhaustive treadmill exercise and recovery did not reveal significant differences (Figs. 1, 2, and 3). Anaerobic contributions to very brief and (or) submaximal exercise may consist more of stored highenergy phosphates as compared with rapid glycolysis with lactate production. Anaerobic energy expenditure as interpreted by blood lactate and excess CO2 production at the lower and moderate workloads often indicated little to no rapid substrate level ATP turnover. Thus, although rapid glycolysis with lactate production may fuel ATP turnover at © 2006 NRC Canada

148 Fig. 2. The figure represents 4 estimations of total energy expenditure where exercise was performed at rates that equaled VO2 max (the exercise was not exhaustive). Resting O2 uptake was subtracted from all exercise and EPOC data. Data for 2, 4, and 10 s time periods are not different among estimations. Significant differences are evident at 15 s: *, estimation is significantly different from all others (p < 0.05).

the start of muscle contraction (Greenhaff and Timmons 1998; Shulman and Rothman 2001; Spriet 1995), it may not leave the muscle in sufficient quantities or may be minimal and so would not significantly contribute to the estimate of total energy expenditure for very brief exercise. “Excess CO2” is not a validated means of estimating anaerobic energy expenditure and has been included only to further test the merit of the hypothesis that measurements solely of O2 uptake can misrepresent total energy expenditure. It also is possible that our conversion for CO2 (1 L CO2 = 20.9 kJ) at the briefest workloads was too low. For example, when fat is used as a substrate, the conversion is 1 L CO2 ~ 27.7 kJ (Blaxter 1989; Kleiber 1975); it is unclear what the CO2 conversion to kJ is when lactate is oxidized. Our findings for very brief (2–10 s) non-exhaustive exercise do not support the hypothesis and suggest that energy expenditure for this type of activity can be quantified by traditional means; that is, solely with O2 uptake measurements (i.e., exercise O2 uptake + O2 debt). The O2 deficit often indicated the largest anaerobic and total energy expenditure. This may be because we used the findings of Bangsbo et al. (1990) who describe the O2 deficit and debt relationships of exhaustive one-legged “kicking” as compared with non-exhaustive 2-legged treadmill exercise. Moreover, estimating the relative ATP or PC component as 20% of EPOC for all exercise bouts in the current investigation was likely incorrect. The O2 deficit is perhaps the most problematic in partitioning high-energy phosphate and rapid glycolytic contributions (blood lactate and excess CO2 measures estimate rapid glycolytic ATP turnover only, ATP and PC stores are quantified as part of EPOC). When the higher exercise intensities were coupled with the longest exercise times (Figs. 2 and 3) O2 debt methodology indicated significantly lower total energy expenditure as compared with all other estimations. Our findings for exercise of higher intensity and increasing duration support the

Appl. Physiol. Nutr. Metab. Vol. 31, 2006 Fig. 3. The figure represents 4 estimations of total energy expenditure performed at rates that were twice that of VO2 max (exercise was not exhaustive). Resting O2 uptake was subtracted from all exercise and EPOC data. Data for 2, 4, and 10 s time periods are not different between interpretations. Significant differences are evident at 15 s: #, O2 deficit estimate is different from the O2 debt estimate (p < 0.05); *, O2 debt estimate is significantly less than other estimates (p < 0.05). Sprinting for 30 s at 200% VO2 max was close to exhaustive, therefore, the elevated excess CO2 levels that exceeded the O2 deficit was probably caused not only by the buffering of an accelerated glycolytic ATP turnover, but by significant hyperventilation as well.

hypothesis and are suggestive of the potential value of an estimate of rapid anaerobic glycolytic ATP turnover. The anaerobic data could be highly variable and each estimate no doubt has questionable validity, yet it is also apparent that the glycolytic contribution to ATP turnover is significant for longer lasting high-intensity exercise and cannot be quantified with measures of O2 uptake only (Gaesser and Brooks 1984; Gnaiger and Kemp 1990; Scott and Kemp 2005). To illustrate this point, it was also found that for all estimations both exercise intensity and duration affect total energy expenditure and an interaction between the two exists; this is not a new finding (Gore and Withers 1990; Hagberg et al. 1980). However, the interaction between intensity and duration was originally considered to be part of an “interest on a loan” payment according to O2 debt methodology. Had rapid anaerobic energy transfer (i.e., anaerobic efficiency and energy expenditure) been initially acknowledged as being separate from O2 uptake, it may have led to a different interpretation of anaerobic and total energy expenditure than the original O2 debt hypothesis proposed. In this regard, the interaction between exercise intensity and duration may be more of an interaction between an accelerated anaerobic and aerobic metabolism. Estimates of anaerobic energy expenditure along with O2 uptake may, for example, better interpret the presence or absence of coronary artery disease (Barthelemy et al. 1996); greater exercise inefficiency as the ratio of VO2 to power output decreases, while anaerobic energy expenditure increases above the “anaerobic threshold” during fast, as compared with slow, ramp exercise tests to exhaustion (Scott and Bogdanffy 1998) and an anaerobic source of heat production during the arousal from metabolic torpor (hiber© 2006 NRC Canada

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nation) where measures of O2 uptake only are not solely accountable for whole-body temperature increases (Tucker 1965). Problems continue for all measurement methodologies and subsequent estimations of anaerobic energy expenditure. Submaximal, maximal, and “supramaximal” exercise lasting a few to several seconds may not contain a sufficient amount of rapid substrate-level ATP turnover to significantly influence total energy expenditure. However, as the workload increases, the contribution of rapid substrate level phosphorylation to ATP turnover becomes larger so that the greatest error in quantifying total energy expenditure is concluded to occur not with the method of estimation, but with the omission of a reasonable estimate of anaerobic energy expenditure.

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