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Hormonal responses during intense exercise preceded by glucose ingestion
Canadian Journal of Applied Sport Sciences. Journal Canadien Des Sciences Appliquees Au Sport
|June 1, 1980
Summary
Ingesting glucose before intense exercise (80% VO2max) did not alter cortisol or insulin levels during the activity. However, it did reduce the growth hormone (GH) response, suggesting glucose or insulin can attenuate GH release.
Area of Science:
- Exercise Physiology
- Endocrinology
- Metabolic Research
Background:
- Understanding metabolic and endocrine responses to exercise is crucial for optimizing athletic performance and health.
- Carbohydrate availability significantly impacts exercise physiology, influencing substrate utilization and hormonal regulation.
- Previous research indicates complex interactions between glucose metabolism, insulin sensitivity, and exercise intensity.
Purpose of the Study:
- To investigate the metabolic and endocrine effects of intense exercise under varying carbohydrate availability conditions.
- To examine the impact of pre-exercise glucose ingestion on hormonal responses (insulin, GH, cortisol) during and after exercise.
- To determine if diminished muscle and hepatic glycogen stores influence exercise-induced endocrine changes.
Main Methods:
- Four experimental conditions: rest (R), rest with glucose (RG), exercise (E), and exercise with glucose (EG).
- Intense exercise protocol: 80% VO2max, two 30-minute bouts with a 2-hour rest interval.
- Measurements included blood glucose, insulin, growth hormone (GH), and cortisol levels during and after exercise bouts.
Main Results:
- Pre-exercise glucose ingestion accelerated blood glucose decrease in the initial exercise phase (EG) and led to a sharp insulin decrease.
- An insulin rebound was observed post-exercise in the glucose ingestion group (EG), but not in the normal exercise group (E).
- The exercise-induced growth hormone (GH) increase was diminished in the EG condition compared to E, while cortisol responses remained unchanged across conditions.
Conclusions:
- Moderate depletion of muscle and liver glycogen several hours before exercise does not affect cortisol, GH, or insulin responses during exercise.
- Pre-exercise glucose availability does not alter cortisol or insulin responses during exercise.
- Diminished GH concentrations during exercise with glucose ingestion suggest that glucose and/or insulin attenuate GH release.