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Metabolic adaptations to training precede changes in muscle mitochondrial capacity
H J Green1, R Helyar, M Ball-Burnett
1Department of Kinesiology, University of Waterloo, Ontario, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 1, 1992
Summary
Short-term exercise training rapidly reduces muscle glycogen use and lactate levels. These metabolic adaptations occur early in training and do not require increased muscle mitochondrial capacity.
Area of Science:
- Exercise Physiology
- Skeletal Muscle Metabolism
- Biochemistry
Background:
- Endurance training typically enhances muscle mitochondrial capacity.
- Trained individuals exhibit reduced glycogen utilization and lactate accumulation during exercise.
- The necessity of mitochondrial adaptations for these metabolic changes is not fully understood.
Purpose of the Study:
- To investigate if enhanced muscle mitochondrial capacity is essential for reduced exercise glycogen loss and lactate concentration post-training.
- To examine early metabolic adaptations to short-term exercise training.
Main Methods:
- Nine male subjects underwent 5-7 days of daily cycling (2 hours/day at 67% VO2max).
- Vastus lateralis muscle biopsies were collected before and after training during a graded exercise test.
- Glycogen content and lactate concentration were analyzed at multiple time points during exercise.
Main Results:
- Training significantly reduced muscle glycogen utilization during exercise (P < 0.05).
- Muscle lactate concentrations were significantly lower at 15, 30, and 60 minutes post-training (P < 0.05).
- Maximal aerobic power (VO2max) and key citric acid cycle enzyme activities remained unchanged.
Conclusions:
- Early metabolic adaptations, including reduced glycogenolysis and lactate production, occur rapidly with short-term exercise training.
- These metabolic improvements in exercising humans do not necessitate concurrent increases in muscle mitochondrial enzyme capacity.
- Altered metabolic pathways are early adaptive responses to training in voluntary exercise.