title: Relationship between muscle T2* relaxation properties and metabolic state: a combined localized 31P-spectroscopy and 1H-imaging study.
abstract: A multi-volume 31P-magnetic resonance spectroscopy localization procedure was implemented to compare directly muscle metabolism and proton T2* relaxation properties in the human plantar flexor muscles during exercise. Localized 31P-spectra were collected simultaneously from the medial gastrocnemius, lateral gastrocnemius and soleus muscles during exercise using beta1-insensitive Hadamard Spectroscopic Imaging (HSI). 1H T2*-weighted gradient-echo images were acquired at rest and immediately following high-intensity plantar flexion exercise. T2* mapping of the individual calf muscles showed that plantar flexion with the knee extended produces significant increases (P < 0.0001) in the mean (SEM) T2* of the medial [35.6 (1.2) ms vs 28.5 (0.5) ms at rest] and lateral gastrocnemius [35.6 (0.9) ms vs 26.2 (0.9) ms at rest], but not in the soleus [26.7 (0.6) ms vs 27.3 (0.8) ms at rest]. In accordance with the changes in T2*, the ratio of inorganic phosphate to phosphocreatine (Pi:PCr) and the intracellular muscle pH shifted significantly in the gastrocnemii, while the soleus showed no change in muscle pH and only a moderate increase in Pi-to-Ph. Comparison of spectroscopic and relaxation parameters in both gastrocnemius muscles revealed a significant relationship between post-exercise T2* and intracellular pH (r = 0.72-0.76) and Pi-to-Ph ratios (r = 0.81-0.88) during exercise. Using an improved method of localization, this study confirms the existence of a strong relationship between transverse relaxation properties and the metabolic state in skeletal muscles engaged in heavy exercise.
authors.affiliation: Hospital of the University of Pennsylvania, Department of Rehabilitation Medicine, Philadelphia 19104, USA. kvandenb@mail.med.upenn.edu
authors.forename: K
authors.initials: K
authors.lastname: Vandenborne
authors.forename: G
authors.initials: G
authors.lastname: Walter
authors.forename: L
authors.initials: L
authors.lastname: Ploutz-Snyder
authors.forename: G
authors.initials: G
authors.lastname: Dudley
authors.forename: M A
authors.initials: MA
authors.lastname: Elliott
authors.forename: K
authors.initials: K
authors.lastname: De Meirleir
mesh_terms: D015444:Exercise / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D009119:Muscle Contraction; D009126:Muscle Relaxation; D018482:Muscle, Skeletal / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism
chemical_list: D010710:Phosphates; D010725:Phosphocreatine