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LETTER TO THE EDITOR
One point is the discrepancy between the reported mean pH decrease during the standardized exercise (0.66 ± 0.05 pH units in Con, see Ref. 5) and the 0.75 pH units estimated by Bishop (1) from a reproduction of Fig. 1A of Ref. 5. The mean value reported of 0.66 is correct (5). However, Fig. 1A of Ref. 5 does not reproduce the data accurately. Regrettably, a distortion of the data occurred when Fig. 1A was prepared (5). The following new Fig. 1 reports the data faithfully.
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0.50). Our mean postexercise muscle pH values (6.49 and 6.51 in Con and Alk, respectively) were higher than those obtained in Refs. 3, 6 of 6.41 and 6.40, which is consistent with the fact that our subjects were not fully exhausted. On the other hand, our mean resting values (7.16 and 7.17) using the method of Mannion et al. (4) were high compared with 7.00 (3, 8). The discrepancy can be attributed to the methodology used (homogenizing solution and temperature). Our resting muscle pH and correlation between muscle pH and lactate concentration are in accordance with those of Mannion et al. (4) (7.19–7.20 and our Fig. 2, A and B, respectively). Previously, our group (2) used the methodology of Sahlin et al. (8). At that time, our results (7.01–7.03) were consistent with theirs. Furthermore, we take the opportunity of this letter to draw the reader's attention to the danger of reasoning in terms of 
pH as we did. For instance, our pH of 0.66 does not correspond to a higher proton accumulation than the pH of 0.51 reported in Ref. 3. Indeed, pH decreases from 7.16 to 6.50 and from 6.92 to 6.41 correspond to proton accumulations of 247 and 269 nM, respectively. Reasoning on proton concentrations would have been better. Finally, it is important to keep in mind that a large interindividual variability exits in the muscle pH value reached at exhaustion (3) and in the muscle lactate(+pyruvate) concentrations for a given muscle pH reached (7).
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pH per Joule of work performed. Because the coefficient of variation of pH (20.0%) was almost the same as for WSUP (18.9%) or Wsup-se, we believed that statistically the subjects who had done more work did not necessarily have a lower pH per kiloJoule of work performed. We were not aware of any interdependence between the variables. The elegant way proposed by Bishop to explore the possible spurious nature of a correlation is interesting. Using his method, we obtained correlation coefficients ranged between –0.49 and 0.95 and a mean coefficient of 0.71. At the present time, the correlation shown in Fig. 1 appears to be spurious and should not be considered as an argument for a physiological relationship between supramaximal work capacity and mechanisms of muscle pH regulation. Nevertheless, all the other results of this study argue in favor of such a physiological link. Thus, even if the correlations reported in Fig. 1 of Ref. 5 are spurious, the conclusions drawn from this study remain unchallenged. We thank Dr. Bishop for bringing to our attention the limitations of our statistical analysis, and we apologize to the Journal, the reviewers, and the readers for these oversights.
FOOTNOTES
Address for reprint requests and other correspondence: L. Messonnier, Equipe Modélisation des Activités Sportives, Département STAPS, Université de Savoie, Campus Universitaire, F-73376 Le Bourget du Lac Cedex, France (e-mail: laurent.messonnier{at}univ-savoie.fr)
REFERENCES
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  Corrigendum J Appl Physiol, January 1, 2008; 104(1): 318 - 318. [Full Text] [PDF]
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