Reproducibility assessment of metabolic variables characterizing muscle energetics in Vivo: A ³¹P‐MRS study

Abstract

The purpose of the present study was to assess the reliability of metabolic parameters measured using 31 P magnetic resonance spectroscopy ( 31 P MRS) during two standardized rest-exerciserecovery protocols. Twelve healthy subjects performed the standardized protocols at two different intensities; i.e., a moderate intensity (MOD) repeated over a two-month period and heavy intensity (HEAVY) repeated over a year's time. Test-retest reliability was analyzed using coefficient of variation ( Key words: magnetic resonance spectroscopy; reliability; oxidative capacity; PCr kinetics; exercise Phosphorus-31 nuclear magnetic resonance spectroscopy ( 31 P-MRS) is now widely accepted as the "gold standard" method for noninvasive measurements of energy metabolism in exercising muscle. The analysis of changes in phosphorylated compounds concentrations and intracellular pH during rest-exercise-recovery protocols has provided significant advance in the understanding of underlying mechanisms of muscle energy production (1-4). Given the noninvasiveness of the method, 31 P-MRS enables repeated measurements and has been successfully used in a wide range of situations such as the assessment of therapeutic interventions in patients with metabolic disorders (5-7) and the characterization of training-induced metabolic changes (8 -11). More recently, the dynamics of phosphocreatine (PCr) has been used to evaluate the control of mitochondrial respiration in skeletal muscle (12) or the mechanism underlying the V O 2p slow component (13) typically observed during a high-intensity exercise; i.e., above the lactate threshold. In addition, the rate constant of postexercise recovery kinetics of [PCr] has been used as an index of mitochondrial function (14 -17). In addition to these traditional variables, more sophisticated analyses have been put forth in order to quantify the contribution of oxidative and anaerobic pathways to energy production in exercising muscle (2,18,19).Despite the widespread use of 31 P MRS for muscle energetics investigation, the reproducibility of the corresponding variables has been scarcely investigated. It has actually been investigated through repeated measurements performed 1 week (5) and 4 weeks apart (20). Bendahan et al. (5) reported a good reliability in metabolic parameters when investigated using analysis of variance (ANOVA). However, detection of systematic bias might have been affected by large random error between tests as suggested previously (21). observed large test-retest variability in metabolic parameters measured during steady state phases of moderate isometric plantar flexion exercise. However, kinetics parameters of recovery exhibited a small coefficient of variation (CV Ͻ 9%). In this line, van den Broek et al. (22) reported a low variability (CV Ͻ 11.5%) for the parameters describing the recovery kinetics of PCr and adenosine diphosphate (ADP) in a single subject who repeated the same exercise protocol 10 times. Based on a visual inspection of the kinetics of phosphorylated compounds and pH i...

In vivo 31P spectroscopy by fully adiabatic extended image selected in vivo spectroscopy: A comparison between 3 T and 7 T

“…In our study, comparable reproducibility was found for 2.5 cm isotropic voxels in 3 min 48 s as at 1.5 T for nonlocalized 31 P-MRS using a large surface coil (36). Comparable reproducibility was also found for quantification of NTP by ISIS localization at 1.5 T, but with voxel volumes that were nine times larger and measurement times that were five times longer than in our study (33).…”

Reduced muscle oxidative capacity is independent of O2 availability in elderly people

“…However, this explanation is unlikely to be accurate as it has been demonstrated that O 2 availability had to be dramatically reduced before affecting the PCr recovery kinetics (Haseler et al 2007). A more likely explanation is that the parameters of the PCr recovery kinetics typically exhibit some variability (~10-20 %), due to the procedure of fitting and biological variability (Layec et al 2009), which can probably explain most of this nonsignificant difference between the normoxic and hyperoxic results in the young.…”

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

“…Indeed, we previously documented that our setup exhibits an inherent variability (ϳ15%) in the power output produced because of the subjects' difficulty with fine control of the range of motion throughout a 6-min exercise (39). One can argue that this power output change may confound the results of the present study.…”

“…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).…”