PH HETEROGENEITY DURING EXERCISE IN LOCALIZED SPECTRA FROM SINGLE HUMAN MUSCLES

We investigated whether pH heterogeneity in skeletal muscle during exercise, observed with P-31 nuclear magnetic resonance, represents muscle fiber type heterogeneity. Localized spectra were simultaneously acquired from the soleus, medial, and lateral gastrocnemius using a multi-volume localization technique, the Hadamard spectroscopic imaging (HSI) technique. Contamination of nonselected regions to the localized volumes was <5%. HSI-localized spectra were obtained from the calf muscles of untrained subjects and a small group of athletes. Two plantar flexion exercise protocols were implemented: a ''maximal'' high frequency protocol and a ''steady-state'' protocol at low contraction frequency (0.25 Hz). pH heterogeneity was observed in localized spectra of single muscles during both exercise protocols, as indicated by the large P(i) line width. During maximal exercise the P(i) line width was up to three times wider than the phosphocreatine line width, covering an entire pH unit. During the steady-state exercise, in three subjects the P(i) peak clearly resolved into two distinct peaks, one at low pH and one at high pH. As pH heterogeneity was observed in localized spectra of single muscles during both exercise protocols, it most likely reflects the metabolic heterogeneity between fiber types.