Rebuttal from Dr. Ekblom

Abstract

POINT-COUNTERPOINTRebuttal from Dr. EkblomPublished Online:01 Jan 2009https://doi.org/10.1152/japplphysiol.90844.2008cMoreSectionsPDF (40 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat The reason for not adding late references is that there are no new experiments or support for CGM in the discussion regarding limitation of V̇o2max, only variants on the same theme and discussions about exercise fatigue. The reader can see very easily that our opponents try to escape the fact that while V̇o2max is unchanged, the heart is doing more work in the “120%” than the “105%” situation (3). The heart is not allowed to do so, according the CGM (7), since already at 105% there should be “a wide range of biological signals monitored to ensure that exercise always terminates before loss of homeostasis.” The motor units may have worked submaximally in the 105% but evidently higher in the A+Lspurt, 120 and 140% situation, but CGM predicts a reduction in motor unit activation (7).To convince the reader, Noakes and Marino move from “power” to “amount of work” to disprove findings in our second study. But that is very risky and wrong. If a 350-W maximal two-leg work rate is divided on 100 W for arms and 250 W for legs, work time is doubled, but V̇o2max is the same (1). The A+L exercise doubles aerobic and anaerobic yields compared with that with legs only. As long as work rate is high enough, total work is not a factor for the limitation of V̇o2max.In their article above Noakes and Marino use the Zhou et al. study (10), criticized by us (4), which fits their hypothesis but avoid those that disprove it (2). I believe that SV is limited by the pericardium. Experiments on dogs and pigs clearly show that Q̇ during maximal exercise increases by cutting the pericardium (6, 9). In parallel, V̇o2max increases but aBP is unchanged during maximal exercise after pericardioectomy. It is obvious that aBP is well regulated even after pericardioectomy, which means that the peripheral resistance can be changed in accordance with the availability of V̇o2max during maximal exercise and not the opposite—that the periphery determines cardiac output during maximal dynamic exercise.All experimental facts speak in favor of the concept that the blood flow output from the heart is the critical point in the Fick equation (V̇o2max) during maximal exercise. Our (3) and other (5) experiments show that the heart is not near “loss of homeostasis” during normal maximal dynamic exercise as suggested in CGM.REFERENCES1 Åstrand PO, Saltin B. Maximal oxygen uptake and heart rate in various types of muscular activity. J Appl Physiol 16: 977–981, 1961.Link | ISI | Google Scholar2 Boutcher SH, McLaren PF, Cotton Y, Boutcher Y. Stroke volume response to incremental submaximal exercise in aerobically trained active and sedentary men. Can J Appl Physiol 28: 12–26, 2003.Crossref | Google Scholar3 Elfegoun-Brink T, Kaijser L, Gustafsson T, Ekblom B. Maximal oxygen uptake is not limited by a Central Nervous System Governor. J Appl Physiol 102: 781–786, 2007.Link | ISI | Google Scholar4 Ekblom B, EkblomÖ . Stroke volume and the endurance athlete. Scand J Med Sci Sports 16: 70–71, 2006.Crossref | ISI | Google Scholar5 Gubbström L, Berglund B, Kaijser L. Myocardial blood flow and lactate metabolism at rest and during exercise with reduced arterial oxygen content. Acta Physiol Scand 142: 467–474, 1991.Crossref | PubMed | Google Scholar6 Hammond HK, White FC, Bhargava V, Shabetai R. Heart size and maximal cardiac output are limited by the pericardium. Am J Physiol Heart Circ Physiol 263: 1675–1681, 1992.Link | ISI | Google Scholar7 Noakes TD. Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance. Scand J Med Sci Sports 10: 123–145, 2000.Crossref | PubMed | ISI | Google Scholar8 Noakes TD, Marino FE. Point: Maximal oxygen uptake is limited by a central nervous system governor. J Appl Physiol; doi:10.1152/japplphysiol.90844.2008.Link | ISI | Google Scholar9 Stray-Gundersen J, Musch TA, Haidet CG, Swain DP, Ordway GA, Mitchell JH. The effect of pericardioectomi on maximal oxygen uptake and maximal cardiac output in untrained dogs. Circ Res 58: 523–530, 1986.Crossref | PubMed | ISI | Google Scholar10 Zhou B, Conlee RK, Jensen R, Fellingham GW, George JD, Fisher AG. Stroke volume does not plateau during graded exercise in elite male distance runners. Med Sci Sports Exerc 33: 1849–1854, 2001.Crossref | PubMed | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 106Issue 1January 2009Pages 341-342 Copyright & PermissionsCopyright © 2009 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.90844.2008cHistory Published online 1 January 2009 Published in print 1 January 2009 Metrics