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• W3125509300 abstract "We thank Professor Wackerhage (Wackerhage, 2021) for his laudatory appraisal of our review (Poole et al. 2021). His comments on the contributions of German researchers to blood lactate (La−) measurement during exercise testing reinforce our citations to works of Hollmann and colleagues in both the text and Acknowledgements sections of our work. Those and related citations stand on their own merits. We also noted that the ideas of these researchers were perhaps under-appreciated. Importantly, Professor Wackerhage provides additional details of the German work that are insightful and complementary to our paper. However, beyond these points of agreement, it is perhaps equally interesting to debate points of difference between Professor Wackerhage's interpretations and those that we deduce from the literature. Our contention is that words have meaning. We disagree with the assumption that changes in blood lactate concentration ([La−]) are related to oxygen-limited (‘anaerobic’) metabolism. In this context, just as Wasserman and colleagues (Wasserman et al. 1973) did, the German researchers (Mader et al. 1976) failed to consider the Warburg effect (glycolytic production of La− from glucose even in the presence of oxygen; Warburg et al. 1924) as interpreted in contemporary biology (Poole et al. 2021). Another limitation, perhaps understandably at the time, is that the German investigators neglected to address molecular mechanisms relating oxygen availability to La− turnover during exercise and other conditions. Perhaps closest to a mechanistic explanation of the lactate threshold (LT) is the model of Mader (Mader, 2003). However, while his model is complex, Mader provided no empirical data to support estimates of glycolytic flux and La− production during rest or exercise. Further, there was no parsing of the relative or absolute roles of glycogen or glucose, fibre type recruitment, sex, nutritional status, or catecholamine stimulation on La− appearance (Ra), and disposal (Rd) via oxidation and gluconeogenesis. Perhaps in the letter, if not in the science, Wackerhage's text is unclear with regard to the ‘slow component’ rise in exercise over time. Our review and specific citations (i.e. Poole & Jones, 2012) provided a more precise and contemporary treatment of that subject. Whereas the mechanistic bases for the slow component remain to be fully elucidated, its presence was indeed noted in Mader's model (Mader, 2003). Unfortunately, the underlying cause considered by Mader, that decreasing pH inhibits glycolytic ATP synthesis forcing a greater oxidative ATP synthesis, is unable to account quantitatively for the very large slow component that can be observed (up to 1 litre O2 min−1) (Gaesser & Poole, 1996). More recent studies show that a large increase in ATP demand (e.g. Cannon et al. 2014) accompanies the slow component observed only during exercise above LT. Thus, Mader's model does not address the mechanisms for the markedly decreased work efficiency above the LT, and especially above critical power (CP). It is also pertinent that the boundary conditions for muscle are harnessed by cardiovascular limitations in Mader's model without consideration of other potential sites such as cellular diffusion from red blood cells to muscle mitochondria, or even mitochondrial limitations per se (e.g. Roca et al. 1992). Because Ra and Rd are in balance at the maximal La− steady-state (MLSS), in our review we did address that concept acknowledging fully that dynamics of La− turnover and disposal via oxidation and gluconeogenesis are masked using static measurements of blood [La−]. The anecdote on testing of Eddie Merckx in Cologne is interesting, but it provides no additional information on the mechanism of blood lactate turnover. Among our citations, San-Millan & Brooks (2018) considered similar data on Pro Tour Cyclists including Miguel Induráin. In that paper blood [La−] data were interpreted in terms of La− clearance rather than anaerobiosis. In our review we acknowledged differences between blood La− determinations as practiced in Europe and cardiopulmonary assessments as practiced in the USA and elsewhere. Both are important, but they provide different sets of information particularly in the setting of cardio-pulmonary medicine. In his letter, Professor Wackerhage focused on the significance of the 4 mm blood [La−], but admitted that support for it was empirical, not mechanistic. In our review we provided a major section on the plethora of ‘thresholds’, their usage and relationship, or lack thereof, to the CP concept. We assure Professor Wackerhage that the ideas of Mader and others ((a)–(d) in Professor Wackerhage's letter) were considered but not presented, in part, because: (1) the point was already made that linking the performance (power, speed) of a task to an absolute [La−] is a better indicator of endurance capability than ; (2) the notion that an absolute blood [La−] of 4 mm can discriminate among discrete exercise intensity domains (i.e. moderate–heavy–severe) is incorrect for several reasons: for instance, there is substantial heterogeneity of absolute [La−] across individuals at the LT and CP, and [La−] during exercise is impacted by diet, prior exercise, muscle glycogen stores and sampling site as well as multiple other factors that impact La− Ra and Rd (e.g. Poole et al. 2021); and (3) whereas training adaptations based upon [La−] may have considerable utility, it is notable that, at least for non-elite athletes, training outcomes (LT and ) are not necessarily dependent upon training at a certain [La−] (Poole & Gaesser, 1985). In our basic research to identify pathways of La− disposal in resting and exercising individuals, we purposefully clamp blood [La−] to 4 mm by exogenous infusion. That practice exposes differences in the physiological responses to hydrogen ions and the conjugate base anion, La−. However, it is noted that, whereas the MLSS is notionally similar to CP, neither ‘threshold’ necessarily occurs at an absolute 4 mm [La−], with different individuals’ MLSS [La−] values varying from <3 to >5 mm (e.g. Heck et al. 1985). Moreover, a consortium of humoral, pulmonary gas exchange and intramuscular indices supports the proposition that CP provides a superior estimate of the heavy–severe exercise intensity boundary in comparison to MLSS (Vanhatalo et al. 2016; Jones et al. 2019; Galan-Rioja et al. 2020). In summary, we welcome Professor Wackerhage's commentary as it serves to acknowledge contributions of esteemed German researchers to science and medicine. Our review on the basic biology of La− metabolism with applications to sports and clinical medicine is in addition to the works described by Wackerhage. No competing interests declared. All authors have read and approved the final version of this manuscript and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed. None." @default.
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• W3125509300 date "2021-01-25" @default.
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• W3125509300 title "Reply from David Poole, Harry Rossiter, George Brooks and L. Bruce Gladden" @default.
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• W3125509300 doi "https://doi.org/10.1113/jp281169" @default.
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