Simultaneous 31P MRS of the soleus and gastrocnemius in Sherpas during graded calf muscle exercise

• DOI: 10.1152/ajpregu.1997.273.3.r999
• Publication Date: 2017-12-24T19:46:58Z
• Authors: P. S. Allen; G. O. Matheson; G. Zhu; D. Gheorgiu; R. S. Dunlop; T. Falconer; C. Stanley; P. W. Hochachka
• Keywords: Creatine; Gastrocnemius muscle

The observation that the amount of lactate formed during hypobaric hypoxia decreases with severity has become known as "lactate paradox." We used noninvasive 31P magnetic resonance spectroscopy (MRS) to further probe this problem and explore nature muscle metabolism rest-exercise-recovery transitions in Sherpas indigenous high Himalayas Nepal. MRS data were obtained using a whole body 1-m bore, 1.5-T Phillips Gyroscan spectrometer. Muscle-specific localization acquisition was achieved by means modified image-selected vivo sequence (ISIS). spectra acquired from medial lateral gastrocnemius muscle, rich fast-twitch fibers, well constrained selective excitation boundary leg. third region contained signals predominantly soleus, mainly slow-twitch fibers. quantified relative concentration changes phosphocreatine (PCr), Pi, ATP series calf work bouts; free ADP concentrations calculated on assumption creatine phosphokinase reaction always essentially at equilibrium. Hydrogen ion chemical shift which represents equilibrium between mono- diprotonated phosphate. Plantar flexion ergometer designed for operation within magnet. found rigorously regulated thus did not change despite large turnover rates required through exercise. PCr Pi linear functions percent maximum rate gastrocnemius, but transition exercise fractional these metabolites much less than rates. relationship complex; again, kinetic order 1 observed. In contrast soleus sustained smaller crucial rest-work-recovery transitions. Unlike situation most other muscles fibers characterized lactate-associated acidosis work, intracellular pH stable protocols, is consistent low production (i.e., paradox) observed highlanders.