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Commentaries on Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance
2018; American Physiological Society; Volume: 125; Issue: 2 Linguagem: Inglês
10.1152/japplphysiol.00638.2018
ISSN8750-7587
AutoresKyle R. Barnes, Andrew E. Kilding, Richard C. Blagrove, Glyn Howatson, Philip R. Hayes, Jan Boone, Jan Bourgois, Jared R. Fletcher, Brian R. MacIntosh, Fernando González‐Mohíno, Inmaculada Yustres, Daniel Juárez Santos‐García, José María González Rave, James Hopker, D. A. Coleman, Hugo A. Kerhervé, Colin Solomon, Davide Malatesta, Stefano Lanzi, Aitor Fernandez-Menendez, Fabio Borrani, Gareth N. Sandford, Ed Maunder, Craig McNulty, Robert A. Robergs, Gaspare Pavei, Tatiane de Oliveira Barreto, Michael Ramon de Lima Conceição, Diego Santos Souza, Matthew S. Tenan, Duncan J. Macfarlane, Andrew C Hackney, Emily M. Adamic, Ren‐Jay Shei, Jessica A. Freemas, Matthew J. Barenie, Jacob Barton, Zane Yeager, Madeleine K. Nowak, Hunter L. Paris, Timothy D. Mickleborough,
Tópico(s)Muscle metabolism and nutrition
ResumoViewpointCommentaries on Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performancePublished Online:23 Aug 2018https://doi.org/10.1152/japplphysiol.00638.2018MoreSectionsPDF (92 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat COMMENTARY ON VIEWPOINT: USE AEROBIC ENERGY EXPENDITURE INSTEAD OF OXYGEN UPTAKE TO QUANTIFY EXERCISE INTENSITY AND PREDICT ENDURANCE PERFORMANCEKyle R. Barnes1 and Andrew E. Kilding2.Author Affiliations1Department of Movement Science, Grand Valley State University, Allendale, Michigan.2Sports Performance Research Institute New Zealand, Auckland University of Technology, Auckland, New Zealand.to the editor: The issue of defining and expressing exercise economy is not a new issue (1) but has taken on increasing consideration in recent years (3–5). Running economy (RE) is traditionally represented by the oxygen demand for a given velocity of submaximal running that reflects the metabolic, biomechanical, and neuromuscular components of running without consideration for what portion of that V̇o2 is a function of good or bad mechanics as opposed to being related to differences in metabolism that may exist in different athletes or under different conditions (1). Accordingly, the traditional measure of RE is flawed, as it is determined by multiple variables that are not based on oxygen consumption alone.We agree that expressing RE as aerobic energy expenditure at least accounts for differences in substrate oxidation within and between subjects. As such, researchers can also determine with greater precision the true magnitude of change in RE related to metabolic vs. biomechanical or neuromuscular adaptations. This is particularly relevant in longitudinal studies where multiple adaptations may occur and acute intervention studies (2) that are unlikely to affect substrate utilization but often result in changes in RE. Still, depending on the equation used to calculate energy expenditure, results can vary by >5% (5) making comparisons between studies challenging. Therefore, it is encouraged that studies report VO2 and VCO2 or RER, thereby enabling readers to calculate RE using a common equation (5) as well as allowing comparison of VO2 results to traditional studies and existing normative data (1, 3).REFERENCES1. Barnes KR, Kilding AE. Running economy: measurement, norms and determining factors. Sports Med Open 1: 8, 2015.Crossref | Google Scholar2. Barnes KR, Kilding AE. Strategies to improve running economy. Sports Med 45: 37–56, 2015. doi:10.1007/s40279-014-0246-y. Crossref | PubMed | ISI | Google Scholar3. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar4. Fletcher JR, Esau SP, Macintosh BR. Economy of running: beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. doi:10.1152/japplphysiol.00307.2009. Link | ISI | Google Scholar5. Kipp S, Byrnes WC, Kram R. Calculating metabolic energy expenditure across a wide range of exercise intensities: the equation matters. Appl Physiol Nutr Metab 43: 639–642, 2018. doi:10.1139/apnm-2017-0781. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Barnes KR, Kilding AE. Running economy: measurement, norms and determining factors. Sports Med Open 1: 8, 2015.Crossref | Google Scholar2. Barnes KR, Kilding AE. Strategies to improve running economy. Sports Med 45: 37–56, 2015. doi:10.1007/s40279-014-0246-y. Crossref | PubMed | ISI | Google Scholar3. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar4. Fletcher JR, Esau SP, Macintosh BR. Economy of running: beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. doi:10.1152/japplphysiol.00307.2009. Link | ISI | Google Scholar5. Kipp S, Byrnes WC, Kram R. Calculating metabolic energy expenditure across a wide range of exercise intensities: the equation matters. Appl Physiol Nutr Metab 43: 639–642, 2018. doi:10.1139/apnm-2017-0781. Crossref | PubMed | ISI | Google ScholarQUANTIFICATION OF EXERCISE INTENSITY AS ENERGY EXPENDITURE: RELIABILITY AND UNITS OF MEASUREMENTRichard C. Blagrove,12 Glyn Howatson,23 and Philip R. Hayes2.Author Affiliations1Faculty of Health, Education and Life Sciences, Birmingham City University, Birmingham, United Kingdom.2Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle-upon-Tyne, United Kingdom.3Water Research Group, Northwest University, Potchefstroom, South Africa.to the editor: The Viewpoint (1) offered by Beck and colleagues is timely and to be commended given the high number of investigations that utilize oxygen uptake-related outcome measures. When study participants are compared across different time points, for example in a crossover or intervention study design, it is typical to request that a similar diet and exercise regimen are adopted in the 48 h preceding each physiological assessment; however, in reality this may be impractical to monitor accurately. Accounting for substrate utilization within a calculation of metabolic cost therefore probably provides a more valid strategy to quantify exercise intensity (5). We also recently showed that energy cost is a more reliable metric for quantification of running economy compared with oxygen cost in high-performing adolescent distance runners (2). The authors (1) identify that energy expenditure should be quantified as a ratio to body mass, which is also typical in the literature, but as a method of normalization for body size has been criticized (3, 4). We would therefore advocate that wherever possible an appropriate scaling exponent for the population of individuals under investigation, based upon a larger cohort of homogeneous participants (4, 5), is likely to further enhance the validity of energy expenditure measurement. Furthermore, steady-state conditions are a prerequisite for measuring EEaero; too often these are assumed rather than checked (2). Finally, we would recommend that energy cost of exercise is quantified in the international standard (SI) unit for energy, kilojoules, rather than watts or kilocalories.REFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Blagrove RC, Howatson G, Hayes PR. Test-retest reliability of physiological parameters in elite junior distance runners following allometric scaling. Eur J Sport Sci 17: 1231–1240, 2017. doi:10.1080/17461391.2017.1364301. Crossref | PubMed | ISI | Google Scholar3. Curran-Everett D. Explorations in statistics: the analysis of ratios and normalized data. Adv Physiol Educ 37: 213–219, 2013. doi:10.1152/advan.00053.2013. Link | ISI | Google Scholar4. Lolli L, Batterham AM, Weston KL, Atkinson G. Size exponents for scaling maximal oxygen uptake in over 6500 humans: A systematic review and meta-analysis. Sports Med 47: 1405–1419, 2017. doi:10.1007/s40279-016-0655-1. Crossref | PubMed | ISI | Google Scholar5. Shaw AJS, Ingham SA, Folland JP. The valid measurement of running economy in runners. Med Sci Sports Exerc 46: 1968–1973, 2014. doi:10.1249/MSS.0000000000000311. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Blagrove RC, Howatson G, Hayes PR. Test-retest reliability of physiological parameters in elite junior distance runners following allometric scaling. Eur J Sport Sci 17: 1231–1240, 2017. doi:10.1080/17461391.2017.1364301. Crossref | PubMed | ISI | Google Scholar3. Curran-Everett D. Explorations in statistics: the analysis of ratios and normalized data. Adv Physiol Educ 37: 213–219, 2013. doi:10.1152/advan.00053.2013. Link | ISI | Google Scholar4. Lolli L, Batterham AM, Weston KL, Atkinson G. Size exponents for scaling maximal oxygen uptake in over 6500 humans: A systematic review and meta-analysis. Sports Med 47: 1405–1419, 2017. doi:10.1007/s40279-016-0655-1. Crossref | PubMed | ISI | Google Scholar5. Shaw AJS, Ingham SA, Folland JP. The valid measurement of running economy in runners. Med Sci Sports Exerc 46: 1968–1973, 2014. doi:10.1249/MSS.0000000000000311. Crossref | PubMed | ISI | Google ScholarCOMMENTARY ON VIEWPOINT: USE AEROBIC ENERGY EXPENDITURE INSTEAD OF OXYGEN UPTAKE TO QUANTIFY EXERCISE INTENSITY AND PREDICT ENDURANCE PERFORMANCEJan Boone, and Jan Bourgois.Author AffiliationsDepartment of Movement and Sports Science, Ghent University, Ghent, Belgium.to the editor: Beck et al. (1) raise an important point in the use of caloric expenditure to quantify movement economy (kcal·km−1·kg−1 instead of ml·km−1·kg−1) and thus to predict performance and evaluate determinants. However, the calculated caloric equivalent (Eaero) for (sub)maximal oxygen uptake (V̇o2) values would not solve the common problems associated with prescribing exercise (training) intensities based on percentages of maximal V̇o2 (%V̇o2max) or maximal heart rate (%HRmax) (2). A given (%V̇o2max), but also % of maximal Eaero, can result in a high interindividual variance in metabolic stress, given that the relative intensity at which the exercise thresholds (gas exchange threshold and critical power) occur is not fixed and differs between individuals (4). Therefore, an intensity expressed relative to V̇o2max or maximal Eaero, can be above critical power for one subject and below critical power for another. Since critical power is considered as the boundary between the heavy and severe intensity domain, exercise below this threshold results in steady-state responses in V̇o2 and blood lactate concentration, whereas this is not the case for exercise above critical power, where theoretically these values evolve to maximal values (3). Using % of maximal Eaero would not solve this problem. It can be assumed that prescribing exercise intensities relative to the exercise thresholds would induce a more comparable metabolic and respiratory response between individuals and possibly could account in some part of the strong interindividual differences in the adjustments to a similar training program (2).REFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Mann T, Lamberts RP, Lambert MI. Methods of prescribing relative exercise intensity: physiological and practical considerations. Sports Med 43: 613–625, 2013. doi:10.1007/s40279-013-0045-x. Crossref | PubMed | ISI | Google Scholar3. Poole DC, Jones AM. Oxygen uptake kinetics. Compr Physiol 2: 933–996, 2012. Crossref | PubMed | ISI | Google Scholar4. Scharhag-Rosenberger F, Meyer T, Gässler N, Faude O, Kindermann W. Exercise at given percentages of VO2max: heterogeneous metabolic responses between individuals. J Sci Med Sport 13: 74–79, 2010. doi:10.1016/j.jsams.2008.12.626. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Mann T, Lamberts RP, Lambert MI. Methods of prescribing relative exercise intensity: physiological and practical considerations. Sports Med 43: 613–625, 2013. doi:10.1007/s40279-013-0045-x. Crossref | PubMed | ISI | Google Scholar3. Poole DC, Jones AM. Oxygen uptake kinetics. Compr Physiol 2: 933–996, 2012. Crossref | PubMed | ISI | Google Scholar4. Scharhag-Rosenberger F, Meyer T, Gässler N, Faude O, Kindermann W. Exercise at given percentages of VO2max: heterogeneous metabolic responses between individuals. J Sci Med Sport 13: 74–79, 2010. doi:10.1016/j.jsams.2008.12.626. Crossref | PubMed | ISI | Google ScholarEXERCISE INTENSITY SHOULD BE QUANTIFIED RELATIVE TO THE ANAEROBIC THRESHOLD, RATHER THAN MAXIMAL OXYGEN UPTAKEJared R. Fletcher12 and Brian R. MacIntosh1.Author Affiliations1Human Performance Laboratory, Faculty of Kinesiology. University of Calgary. Calgary, AB, Canada.2W21C Research and Innovation Centre, O’Brien Institute of Public Health, Cumming School of Medicine. University of Calgary. Calgary, AB, Canada.to the editor: Oxygen uptake (V̇o2) measurement permits estimation of the energy cost of exercise. Beck et al. (1) criticize the common practice of reporting V̇o2 and support the return to calculating the energy cost as we have proposed (2). We demonstrated that expression of running economy as an energy cost is sensitive to changes in speed and is a more valuable expression of running economy than is V̇o2 (2). This approach avoids the necessity of comparing everyone at the same speed, allowing comparison at a speed relative to lactate threshold. Beck et al. also recommend replacing expression of relative maximal V̇o2 with % maximal aerobic energy supply (%Ėaero max). However, there is a better solution for expression of relative intensity of exercise. The proposed expression (%Ėaero max) does not recognize the anaerobic threshold (AnT), a factor related to regulation of substrate variability and above which aerobic energy does not account for all energy (4). We suggest quantifying exercise intensity relative to the energy cost at anaerobic threshold (%Ėaero AnT), estimated as lactate threshold, critical power, or ventilatory threshold (4). Variability in substrate use is less than when %V̇o2 is used. It is also clear that at intensities above 100%Ėaero AnT, anaerobic energy needs to be accounted for by quantifying lactate accumulation (3). Precision of measurement is improved when V̇o2 is used to estimate energy equivalent below AnT. We encourage our colleagues to calculate energy cost and promote the use of energy cost measured relative to %Ėaero AnT rather than at a common %V̇o2max.REFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Fletcher JR, Esau SP, Macintosh BR. Economy of running: beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. doi:10.1152/japplphysiol.00307.2009. Link | ISI | Google Scholar3. O’Connell JM, Weir JM, MacIntosh BR. Blood lactate accumulation decreases during the slow component of oxygen uptake without a decrease in muscular efficiency. Pflugers Arch 469: 1257–1265, 2017. doi:10.1007/s00424-017-1986-y. Crossref | PubMed | ISI | Google Scholar4. Svedahl K, MacIntosh BR. Anaerobic threshold: the concept and methods of measurement. Can J Appl Physiol 28: 299–323, 2003. doi:10.1139/h03-023. Crossref | PubMed | Google ScholarREFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Fletcher JR, Esau SP, Macintosh BR. Economy of running: beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. doi:10.1152/japplphysiol.00307.2009. Link | ISI | Google Scholar3. O’Connell JM, Weir JM, MacIntosh BR. Blood lactate accumulation decreases during the slow component of oxygen uptake without a decrease in muscular efficiency. Pflugers Arch 469: 1257–1265, 2017. doi:10.1007/s00424-017-1986-y. Crossref | PubMed | ISI | Google Scholar4. Svedahl K, MacIntosh BR. Anaerobic threshold: the concept and methods of measurement. Can J Appl Physiol 28: 299–323, 2003. doi:10.1139/h03-023. Crossref | PubMed | Google ScholarCOMMENTARY ON VIEWPOINT: USE AEROBIC ENERGY EXPENDITURE INSTEAD OF OXYGEN UPTAKE TO QUANTIFY EXERCISE INTENSITY AND PREDICT ENDURANCE PERFORMANCEFernando González-Mohíno, Inmaculada Yustres, Daniel Juárez Santos-García, and José María González-Ravé.Author AffiliationsUniversity of Castilla-La Mancha, Sport Training Lab, Toledo, Spain.to the editor: We appreciate the Viewpoint of Beck et al. (1) providing information about the use of aerobic energy expenditure to quantify exercise intensity in endurance performance. The use of energy cost of running (kcal or kJ·kg−1·km−1) has grown because it is well known that this method is more sensitive to changes in speed than oxygen uptake (3).Recently, we evaluated the Skyrunner World Series’s female winner in 2016 (unpublished data) in our laboratory. The oxygen and energy cost of running were measured during seven workloads (9–15 km/h; <1.00 RER) on treadmill, showing different slopes against workload when plotted. The oxygen cost of running exhibited a linear increase (30.87, 34.72, 35.90, 38.77, 43.06, 47.87, 50.22 ml·kg−1·min−1), while the energy cost of running exhibited a U-shape curve (4.33, 4.30, 4.06, 4.02, 4.13, 4.29, 4.23 kj·kg−1·km−1). During the intermediate workloads, the substrate oxidation remained constant while the oxygen cost increased (0.90, 0.93, 0.93, 0.93, 0.94, 0.96, 0.99 RER). Therefore, the energy cost decreased in these workloads, showing more economical intensities compared with the previous and later workloads. These economical intensities are similar to the competition and also to the majority of training intensities carried out by our subject. These results allow hypothesizing that runners are more economical at the speed they tend to train (2, 4). Definitely, we recommend like Beck et al. (1) to report V̇o2, V̇co2, and RER values to a better comprehension about the results and conclusions of the future studies.REFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Daniels J, Daniels N. Running economy of elite male and elite female runners. Med Sci Sports Exerc 24: 483–489, 1992. doi:10.1249/00005768-199204000-00015. Crossref | PubMed | ISI | Google Scholar3. Fletcher JR, Esau SP, Macintosh BR. Economy of running: beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. doi:10.1152/japplphysiol.00307.2009. Link | ISI | Google Scholar4. Jones AM, Carter H. The effect of endurance training on parameters of aerobic fitness. Sports Med 29: 373–386, 2000. doi:10.2165/00007256-200029060-00001. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Daniels J, Daniels N. Running economy of elite male and elite female runners. Med Sci Sports Exerc 24: 483–489, 1992. doi:10.1249/00005768-199204000-00015. Crossref | PubMed | ISI | Google Scholar3. Fletcher JR, Esau SP, Macintosh BR. Economy of running: beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. doi:10.1152/japplphysiol.00307.2009. Link | ISI | Google Scholar4. Jones AM, Carter H. The effect of endurance training on parameters of aerobic fitness. Sports Med 29: 373–386, 2000. doi:10.2165/00007256-200029060-00001. Crossref | PubMed | ISI | Google ScholarCAN AEROBIC ENERGY EXPENDITURE BE USED INSTEAD OF OXYGEN UPTAKE TO BETTER PREDICT ENDURANCE PERFORMANCE?James G. Hopker1 and Damian A. Coleman2.Author Affiliations1School of Sport and Exercise Sciences, University of Kent, Chatham Maritime, Kent, England.2School of Human and Life Sciences, Canterbury Christ Church University, Canterbury, Kent, England.to the editor: We agree with Beck et al. (1) that aerobic energy expenditure has the potential to provide a superior prediction of performance than V̇o2 alone, due to the consideration of energy yield per liter of O2. Therefore, given our interest in cycling efficiency and the fact that Beck et al. (1) use hypothetical data within their Viewpoint, we decided to test their proposition using data we collected in a previous study (2). Our study investigated the relationship between cycling efficiency and 1 h cycling time trial performance in trained cyclists. Within our study we also measured lactate threshold using an incremental cycling test. Using this data and the Ėaero equation provided by Beck et al. (1), we sought to predict our cyclist’s 1 h time trial performance from both the V̇o2 (ml O2·kg−1·min−1) at LT, and aerobic energy expenditure. Ėaero (J/ml O2) was significantly positively correlated with mean 1-h cycling time trial performance (239 ± 39 W; r = 0.71; P = 0.007), explaining ~51% of the variation between cyclists. However, in our data, Ėaero was not able to predict performance to any greater extent than the V̇o2 at LT (r = 0.73; P = 0.005), explaining ~53% of the variance. Therefore, although we agree with the approach taken by Beck et al. (1) and support the view that aerobic energy expenditure might be a better measure of exercise intensity and endurance performance, our data do not support the proposition that it provides a better prediction of performance than V̇o2 at LT.REFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Hopker JG, Coleman DA, Gregson HC, Jobson SA, Von der Haar T, Wiles J, Passfield L. The influence of training status, age, and muscle fiber type on cycling efficiency and endurance performance. J Appl Physiol (1985) 115: 723–729, 2013. doi:10.1152/japplphysiol.00361.2013. Link | ISI | Google ScholarREFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Hopker JG, Coleman DA, Gregson HC, Jobson SA, Von der Haar T, Wiles J, Passfield L. The influence of training status, age, and muscle fiber type on cycling efficiency and endurance performance. J Appl Physiol (1985) 115: 723–729, 2013. doi:10.1152/japplphysiol.00361.2013. Link | ISI | Google ScholarSUPERIOR BUT STILL LIMITED METRICSHugo A. Kerhervé1 and Colin Solomon2.Author Affiliations1M2S Laboratory, Univ Rennes, France.2School of Health and Sport Sciences, University of the Sunshine Coast, Australia.to the editor: Beck et al. (1) provide a clear and compelling rationale to progress beyond the use of oxygen consumption (its maximal rate, sustainable fraction) or economy (cost per unit distance) as primary indicators of absolute and relative exercise intensity and to use an energetic approach in explanatory perspectives of exercise capacity and performance.Quantifying economy using energy units has been popular in research on prolonged exercise and has allowed for the characterization of the small, near-constant increases in running economy up to marathon distance (2). However, the wide range of changes in running economy observed in ultramarathons (low to high decreases or even improvements) suggests neuromuscular and muscle ultrastructural factors, among others, may confound the magnitude of the measured cardiorespiratory alterations (3).Recommendations to determine relative exercise intensities as a percentage of the maximum rate of energy expenditure are novel. Although we concur that these metrics could be used to better characterize true physiological capacity in some situations (setting intensity as a percentage of maximum), they would still need to be used in conjunction with relevant turnpoints (thresholds; including respiratory gas exchange) and are associated with the same limitations as oxygen consumption based calculations when applied to any ultraendurance exercise.Overall, sufficient detail in primary (oxygen consumption, ventilation) and secondary [respiratory exchange ratio, or ventilatory efficiency (V̇e÷V̇o2)] cardiorespiratory variables should still be provided to allow researchers to interpret and compare findings from laboratory and field studies in the context of inherent differences in pacing strategies, environmental conditions, and training status.REFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Brueckner JC, Atchou G, Capelli C, Duvallet A, Barrault D, Jousselin E, Rieu M, di Prampero PE. The energy cost of running increases with the distance covered. Eur J Appl Physiol Occup Physiol 62: 385–389, 1991. doi:10.1007/BF00626607. Crossref | PubMed | ISI | Google Scholar3. Vernillo G, Millet GP, Millet GY. Does the running economy really increase after ultra-marathons? Front Physiol 8: 783, 2017. doi:10.3389/fphys.2017.00783. Crossref | PubMed | ISI | Google ScholarREFERENCES1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Brueckner JC, Atchou G, Capelli C, Duvallet A, Barrault D, Jousselin E, Rieu M, di Prampero PE. The energy cost of running increases with the distance covered. Eur J Appl Physiol Occup Physiol 62: 385–389, 1991. doi:10.1007/BF00626607. Crossref | PubMed | ISI | Google Scholar3. Vernillo G, Millet GP, Millet GY. Does the running economy really increase after ultra-marathons? Front Physiol 8: 783, 2017. doi:10.3389/fphys.2017.00783. Crossref | PubMed | ISI | Google ScholarUSE AEROBIC ENERGY EXPENDITURE INSTEAD OF OXYGEN UPTAKE TO QUANTIFY METABOLIC RATE AND COST OF EXERCISE: INTENSITY MATTERSDavide Malatesta,1 Stefano Lanzi,23 Aitor Fernandez-Menendez,1 and Fabio Borrani1.Author Affiliations1Institute of Sport Sciences (ISSUL), Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.2Division of Angiology, Heart and Vessel Department, Lausanne University Hospital, Lausanne, Switzerland.3Service of Endocrinology, Diabetes and Metabolism, Lausanne University Hospital, Lausanne, Switzerland.to the editor: Since the classical and seminal study of Margaria (4), the energy expenditure of locomotion (i.e., running and walking at different speeds and gradients) was expressed in kilocalories per minute (i.e., metabolic rate or metabolic power). By using indirect calorimetry, the oxygen uptake assessed during the exercise steady state, was then transformed from ml O2/min into kcal/min, taking into account the energy equivalent of 1 liter of oxygen. The results of this precursor study showed that the net energy cost of level walking (i.e., the energy spent per unit of distance covered) was ~0.5 kcal·kg−1·km−1 and the net energy cost of level running was ~1 kcal·kg−1·km−1. According to Beck et al. (1), the metabolic rate or energy cost of exercise should be expressed in units of aerobic energy rather than oxygen to take into account difference in substrate utilization during exercise. For instance, this may be very important when comparing, at the same relative exercise intensities, lean and obese individuals for whom the substrate oxidation during exercise differs (3). However, although indirect calorimetry is extensively used to assess energy expenditure during exercise, changes in the size of the bicarbonate pools may interfere with the calculation of substrate oxidation and thus energy expenditure at high exercise intensities (2). Therefore, it should be limited to exercise intensities lower than the 85% of the maximal oxygen uptake (5). For this reason, we are more skeptical to report maximal aerobic capacity and exercise intensity using units of aerobic energy as suggested by Beck et al. (1).References1. Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol (1985). doi:10.1152/japplphysiol.00940.2017. Link | ISI | Google Scholar2. Ferrannini E. The theoretical bases of indirect calorimetry: a review. Metabolism 37: 287–301, 1988. doi:10.1016/0026-0495(88)90110-2. Crossref | PubMed | ISI | Google Scholar3. Lanzi S, Codecasa F, Cornacchia M, Maestrini S, Salvadori A, Brunani A, Malatesta D. Fat oxidation, hormonal and plasma metabolite kinetics during a submaximal incremental test in lean and obese adults. PLoS One 9: e88707, 2014. doi:10.1371/journal.pone.0088707. Crossref | PubMed | ISI | Google Scholar4. Margaria R. Sulla fisiologia e specialmente sul consumo energetico della marcia e della corsa a varia velocita’ ed inclinazione del terreno. Atti Accad Naz Lincei 7: 299–368, 1938.Google Scholar5. Romijn JA, Coyle EF, Hibbert J, Wolfe RR. Comparison of indirect calorimetry and a new breath 13C/12C ratio meth
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