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Gender differences in glucose kinetics and substrate oxidation during exercise near the lactate threshold
Brent C Ruby1, Andrew R Coggan, Ted W Zderic
1Human Performance Laboratory, University of Montana, Missoula, Montana 59812-1825, USA. ruby@selway.umt.edu
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 14, 2002
Summary
Men and women show similar plasma glucose kinetics during exercise relative to lactate threshold (LT). However, women rely more on blood glucose, while men utilize more muscle glycogen for energy during these workouts.
Area of Science:
- Exercise Physiology
- Metabolic Studies
- Human Performance
Background:
- Understanding substrate utilization during exercise is crucial for optimizing athletic performance and metabolic health.
- Sex-based differences in substrate metabolism during exercise are not fully elucidated, particularly concerning glucose kinetics relative to lactate threshold (LT).
Purpose of the Study:
- To investigate and compare plasma glucose kinetics and substrate oxidation patterns between men and women during moderate-intensity exercise at 70% and 90% of VO(2) at LT.
- To determine if sex influences the reliance on muscle glycogen versus blood glucose for energy production during exercise at varying intensities relative to LT.
Main Methods:
- Utilized a primed constant infusion of [6,6-(2)H]glucose to measure plasma glucose appearance (R(a)) and disappearance (R(d)).
- Subjects performed 25-minute cycling bouts at 70% and 90% of their individual lactate threshold (LT).
- Measured oxygen uptake (VO(2)) and calculated substrate oxidation rates, including the contribution of carbohydrate (CHO) and muscle glycogen.
Main Results:
- No significant differences were observed in plasma glucose R(a) or R(d) between men and women at either 70% or 90% LT.
- While the overall contribution of carbohydrate (CHO) to energy expenditure was similar between sexes, women showed a lower relative contribution from muscle glycogen oxidation compared to men.
- Consequently, women exhibited a significantly higher relative contribution of blood glucose to total CHO oxidation during exercise at both intensities relative to LT.
Conclusions:
- Plasma glucose kinetics (appearance and disappearance) are comparable between men and women during exercise at 70% and 90% LT.
- Significant sex-based differences exist in substrate utilization, with women relying more heavily on blood glucose and less on muscle glycogen for energy during moderate-intensity exercise relative to LT.
- These findings highlight distinct metabolic adaptations to exercise between sexes, impacting fuel source selection during sustained physical activity.