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pH heterogeneity during exercise in localized spectra from single human muscles
K Vandenborne1, G Walter, J S Leigh
1Department of Radiology, University of Pennsylvania, Philadelphia 19104.
The American Journal of Physiology
|November 1, 1993
Summary
Skeletal muscle pH heterogeneity during exercise, detected using 31P magnetic resonance, likely reflects differences between muscle fiber types. This finding provides insight into muscle metabolism during physical activity.
Area of Science:
- Exercise Physiology
- Skeletal Muscle Metabolism
- Biophysics
Background:
- Skeletal muscle exhibits metabolic complexity during exercise.
- Previous studies using 31P nuclear magnetic resonance (NMR) have indicated pH heterogeneity within muscles during physical exertion.
- The source of this observed pH heterogeneity remains incompletely understood.
Purpose of the Study:
- To investigate if pH heterogeneity observed in skeletal muscle during exercise using 31P NMR corresponds to muscle fiber type heterogeneity.
- To characterize the nature of pH changes within single muscles during different exercise intensities.
Main Methods:
- Utilized Hadamard spectroscopic imaging (HSI), a multivolume localization technique, to acquire localized 31P NMR spectra.
- Simultaneously collected spectra from the soleus, medial, and lateral gastrocnemius muscles in untrained subjects and athletes.
- Employed two distinct exercise protocols: a high-frequency maximal exercise and a low-frequency (0.25 Hz) steady-state exercise.
Main Results:
- Observed significant pH heterogeneity within single muscles during both maximal and steady-state exercise protocols, evidenced by a broad inorganic phosphate (Pi) peak.
- During maximal exercise, the Pi peak width was up to three times wider than the phosphocreatine (PCr) peak width, spanning a full pH unit.
- In three subjects during steady-state exercise, the Pi peak resolved into two distinct peaks, indicating populations of muscle fibers at different pH levels.
Conclusions:
- The observed pH heterogeneity within single skeletal muscles during exercise is strongly indicative of underlying metabolic heterogeneity between different muscle fiber types.
- HSI-localized 31P NMR spectroscopy is a viable technique for resolving metabolic differences at the fiber type level during dynamic exercise.
- These findings contribute to a better understanding of muscle fiber recruitment and metabolic specialization during physical activity.