An interleaved heteronuclear NMRI-NMRS approach to non-invasive investigation of exercising human skeletal muscle.

Novel tools are presented that aim at more comprehensive NMR investigations of human skeletal muscle metabolism, in particular during exercise protocols. They integrate imaging (NMRI) and spectroscopy (NMRS) experiments in a single dynamic examination. The first sequence that we propose combine NMR-plethysmography, 1H-NMRS of deoxymyoglobin and 31P-NMRS. This allows simultaneous determination of skeletal muscle perfusion, oxygenation and high-energy phosphates status. It is very well suited to the study of interplay between blood supply and energy metabolism during the recovery period from aerobic or anaerobic exercise. In a second sequence, the same spectroscopic measurements are associated to a 1H double quantum coherence (DQC) edition of lactate. It is, this time, possible to estimate muscle lactate production concurrently with oxygen content, high-energy phosphates distribution and intracellular pH. This sequence is intended mainly for metabolic investigations of ischemic bouts. Examples are given of the use of these sequences in normal adult volunteers. They demonstrate the technical feasibility of these new approaches and illustrate their potential for future applications, particularly non-invasive of regulatory mechanisms of muscle metabolism in situ.