Received: 13 November 2009, Revised: 2 June 2010, Accepted: 23 July 2010, Published online in Wiley Online Library: 19 October 2010 Comparative determination of energy production rates and mitochondrial function using different 31 P MRS quantitative methods in sedentary and trained subjects Gwenael Layec a , Aure ´ lien Bringard b , Yann Le Fur a , Christophe Vilmen a , Jean-Paul Micallef b,c , Ste ´ phane Perrey b , Patrick J. Cozzone a and David Bendahan a * Muscle energetics has been largely and quantitatively investigated using 31 P MRS. Various methods have been used to estimate the corresponding rate of oxidative ATP synthesis (ATP ox ); however, potential differences among methods have not been investigated. In this study, weaimed to compare the rates of ATP production and energy cost in two groups of subjects with different training status using four different methods: indirect method (method 1), ADP control model (method 2) and phosphate potential control model (method 3). Method 4 was a modified version of method 3 with the introduction of a correction factor allowing for similar values to be obtained for the end-exercise oxidative ATP synthesis rate inferred from exercise measurements and the initial recovery phosphocreatine resynth- esis rate. Seven sedentary and seven endurance-trained subjects performed a dynamic standardised rest– exercise–recovery protocol. We quantified the rates of ATP ox and anaerobic ATP synthesis (ATP ana ) using 31 P MRS data recorded at 1.5 T. The rates of ATP ox over the entire exercise session were independent of the method used, except for method 4 which provided significantly higher values in both groups ( p < 0.01). In addition, methods 1–3 were cross-correlated, thereby confirming their statistical agreement. The rate of ATP ana was significantly higher with method 1 ( p < 0.01) and lower with method 4 ( p < 0.01). As a result of the higher rate of ATP ox , EC (method 4) calculated over the entire exercise session was higher and initial EC (method 1) was lower in both groups compared with the other methods. We showed in this study that the rate of ATP ox was independent of the calculation method, as long as no corrections (method 4) were performed. In contrast, results related to the rates of ATP ana were strongly affected by the calculation method and, more exactly, by the estimation of protons generated by ATP ox . Although the absolute EC values differed between the methods, within- or between-subject comparisons are still valid given the tight relationships between them. Copyright ß 2010 John Wiley & Sons, Ltd. Keywords: muscle energetics; exercise; ATP turnover; energy cost; PCr kinetics; oxidative phosphorylation INTRODUCTION Skeletal muscle bioenergetics has been largely investigated noninvasively using 31 P MRS. On the basis of high-energy phosphate metabolites and pH measurements, a large number of publications have been devoted to the quantitative investigation of muscle energetics in patients with muscle diseases (1–3) and of the metabolic effects of training (4–6). Interestingly, many quantitative methods have been devel- oped to estimate oxidative and anaerobic ATP production, buffer capacity and proton efflux, using several different theoretical justifications (7). Given that the underlying control of mitochon- (wileyonlinelibrary.com) DOI:10.1002/nbm.1607 Research Article * Correspondence to: D. Bendahan, Centre de Re ´sonance Magne ´tique Biolo- gique et Me ´dicale, UMR CNRS 6612, Faculte ´ de Me ´decine de Marseille, 27 Bd Jean Moulin, 13005 Marseille, France. a G. Layec, Y. Le Fur, C. Vilmen, P. J. Cozzone, D. Bendahan, P. J. Cozzone, D. Bendahan Centre de Resonance Magnetique Biologique et Medicale, Faculte ´ de Me ´decine de Marseille, Marseille, France b A. Bringard, J.-P. Micallef, S. Perrey Efficience et De ´ficience Motrices, Faculte ´ des Sciences du Sport, Montpellier, France c J.-P. Micallef INSERM ADR 08, Montpellier, France Abbreviations used: ATP ana , anaerobic ATP synthesis; ATP CK , ATP synthesis from creatine kinase reaction; ATP gly , ATP synthesis from anaerobic glycolysis; ATP ox , ATP synthesis from oxidative phosphorylation; CV, coefficient of vari- ation; EC, energy cost; EC ini , initial rate of anaerobic ATP production; EC tot , ratio between oxidative and anaerobic ATP production and power output; H þ b , number of protons passively buffered in the cytosol; H þ CK , number of protons consumed during PCr breakdown; H þ efflux , number of protons leaving the cell; H þ ox , number of protons produced by oxidative phosphorylation; k, first-order PCr recovery rate constant; K m , affinity constant; MVC, maximum voluntary isometric contraction; PCr, phosphocreatine; [PCr] cons , amount of PCr consumed at the end of the exercise session; [PCr] end , concentration of PCr measured at the end of exercise; Pi, inorganic phosphate; PME, phosphomo- noesters; Q max , maximal aerobic capacity; V eff , initial recovery rate of efflux; b total , total buffering capacity. NMR Biomed. 2011; 24: 425–438 Copyright ß 2010 John Wiley & Sons, Ltd. 425