Comparative determination of energy production rates and mitochondrial function using different ³¹P MRS quantitative methods in sedentary and trained subjects

Abstract

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, we aimed 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 resynthesis 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.

In vivoevidence of an age-related increase in ATP cost of contraction in the plantar flexor muscles

“…Recently, Conley et al [3] also reported a coefficient of variation of 60 % for the ATP cost of contraction within a group of older individuals. Such variability between studies and among individuals is probably biological, rather than related to the method of quantification employed, as we recently demonstrated a close agreement between several 31 P-MRS approaches developed to estimate the ATP cost of contraction during dynamic exercise in humans [28]. In addition, it should be kept in mind that numerous muscles are involved in human locomotion and age-related alterations in muscle efficiency may vary among them.…”

“…At the onset of exercise, ATP generated from oxidative pathways is negligible such that anaerobic ATP synthesis accounts for the entire ATP synthesis [14]. The corresponding amount of ATP scaled to power output provides a reliable estimation of the initial rate of total ATP synthesis [27,28].…”

Dynamic 31P–MRSI using spiral spectroscopic imaging can map mitochondrial capacity in muscles of the human calf during plantar flexion exercise at 7 T

“…peripheral arterial disease (PAD)5, 6, 7). These observations, together with the fact that evaluation of muscle oxidative metabolism provides insight into personal training status,8, 9 have led to a considerable methodological development in medical imaging for non‐invasive assessment of muscle energy metabolism.…”

Opposite effects of hyperoxia on mitochondrial and contractile efficiency in human quadriceps muscles

“…Total ATP synthesis generated from aerobic and anaerobic pathways was scaled to the power output (in W) from the leg investigated by the MR coil. Methodological considerations addressing the validity and the reproducibility of the calculation of ATP synthesis rates have been previously addressed by us and others (25,29,31,33,38,39). The ratio of the rate of oxidative ATP synthesis to V O2p was also calculated as an index of mitochondrial efficiency (ATP/V O2).…”

“…Consequently, it has actually been assayed very rarely in humans and only in resting muscle (1,46). Interestingly, we recently developed an experimental setup allowing the simultaneous measurement of pulmonary V O 2 (V O 2p ) (7) and oxidative ATP synthesis rate during knee-extension exercise (38) that can shed some light on mitochondrial efficiency in exercising muscle.…”