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Hormonal and metabolic responses to maintained hyperglycemia during prolonged exercise
D P MacLaren1, T Reilly, I T Campbell
1Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Henry Cotton Campus, Liverpool L3 2ET, United Kingdom. d.p.maclaren@livjm.ac.uk
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 20, 1999
Summary
Maintained hyperglycemia during endurance exercise significantly lowers key stress hormones and increases carbohydrate use. However, it does not spare muscle glycogen stores, indicating increased glucose utilization.
Area of Science:
- Exercise Physiology
- Endocrinology
- Metabolic Studies
Background:
- Understanding the metabolic and hormonal adaptations to exercise under conditions of hyperglycemia is crucial for managing metabolic health.
- Previous research has explored exercise responses in various glucose states, but the specific impact of sustained hyperglycemia on hormonal milieu and substrate utilization during prolonged endurance exercise requires further elucidation.
Purpose of the Study:
- To investigate the effects of maintained hyperglycemia on hormonal and metabolic responses during endurance exercise.
- To determine the maximal rate of glucose utilization (infusion rate) under hyperglycemic conditions.
- To assess the impact of maintained hyperglycemia on muscle glycogen depletion during prolonged exercise.
Main Methods:
- Eight healthy men performed two 120-minute cycle ergometer trials at 70% peak oxygen uptake.
- Trial A involved clamping blood glucose at 12 mmol/l before and during exercise.
- Trial B served as a placebo control, with saline infusion matching trial A's volume and rate.
Main Results:
- Maintained hyperglycemia significantly reduced plasma concentrations of nonesterified fatty acid, glycerol, 3-hydroxybutyrate, epinephrine, norepinephrine, and growth hormone (P < 0.001).
- Plasma insulin concentrations were significantly elevated (P < 0.001) during exercise under hyperglycemia.
- Total carbohydrate oxidation rates were significantly higher in the hyperglycemia trial (P < 0.01), with maximal glucose infusion rates ranging from 1.33 to 2.78 g/min.
Conclusions:
- Maintained hyperglycemia attenuates the hormonal stress response during endurance exercise.
- Hyperglycemia promotes carbohydrate oxidation and glucose utilization during prolonged exercise.
- Muscle glycogen stores are significantly depleted under maintained hyperglycemia, suggesting no glycogen sparing effect.