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Effects of training duration on substrate turnover and oxidation during exercise
S M Phillips1, H J Green, M A Tarnopolsky
1Department of Kinesiology, University of Waterloo, Ontario, Canada.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1996
Summary
Endurance training enhances fat metabolism by increasing intramuscular triglyceride use and reducing glucose oxidation. These adaptations occur progressively, with significant changes observed as early as 5 days of training.
Area of Science:
- Exercise physiology
- Metabolic adaptations
- Nutrient metabolism
Background:
- Prolonged endurance training significantly alters substrate utilization during exercise.
- Understanding these metabolic shifts is crucial for optimizing training protocols and athletic performance.
Purpose of the Study:
- To investigate the adaptations in fat and carbohydrate metabolism following a 31-day endurance training program.
- To examine the time course of these metabolic changes, specifically at 5 and 31 days of training.
Main Methods:
- Utilized stable isotope tracers ([6,6-2H2]glucose, [2H5]glycerol, [2H2]palmitate) to track substrate metabolism.
- Employed cycle ergometry at 60% of pretraining peak oxygen consumption (VO2peak) for 90 minutes.
- Administered tests before training (PRE) and after 5 (5D) and 31 (31D) days of training.
Main Results:
- Exercise increased glucose and glycerol turnover, indicating higher glucose utilization and lipolysis.
- Total fat oxidation increased by 10% at 5D and 58% at 31D, primarily due to enhanced intramuscular triglyceride oxidation.
- Glucose oxidation decreased, and glucose production/utilization were reduced at 31D compared to PRE and 5D.
Conclusions:
- Long-term endurance training progressively increases fat utilization during exercise.
- This adaptation is mediated by greater intramuscular triglyceride oxidation and reduced glucose oxidation.
- Metabolic adaptations begin early (by 5D) and precede increases in mitochondrial enzyme activity.