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Structural basis of muscle O(2) diffusing capacity: evidence from muscle function in situ.
R T Hepple1, M C Hogan, C Stary
1Department of Medicine, University of California at San Diego, La Jolla, California 92093-0623, USA. hepple@ucalgary.ca
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 5, 2000
Summary
Short-term immobilization increases capillary density in skeletal muscle, but this adaptation does not improve oxygen diffusing capacity during intense exercise in dogs.
Area of Science:
- Physiology
- Exercise Physiology
- Skeletal Muscle Biology
Background:
- Muscle oxygen (O2) diffusion limitation impacts maximal O2 uptake.
- The relationship between diffusion distance and O2 uptake is not fully understood.
Purpose of the Study:
- To investigate how changes in diffusion distance, induced by immobilization and training, affect muscle O2 diffusing capacity (Dmus(O2)).
Main Methods:
- Surgically isolated, pump-perfused canine gastrocnemius muscles were stimulated to peak O2 uptake under varying arterial oxygen levels.
- Muscle fiber size and capillary density were analyzed microscopically after experimental interventions (training or immobilization).
Main Results:
- Immobilization significantly reduced muscle fiber size and increased capillary density, shortening diffusion distance.
- Despite increased capillary density, muscle O2 diffusing capacity (Dmus(O2)) did not differ between control, trained, and immobilized muscles.
- Exercise training did not significantly alter capillarity compared to controls.
Conclusions:
- Increased capillary density from short-term immobilization does not enhance muscle O2 diffusing capacity in heavily working skeletal muscle.
- Diffusion distance reduction alone is insufficient to improve O2 diffusing capacity under conditions of high O2 demand.