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Exercise training increases GLUT-4 protein concentration in previously sedentary middle-aged men
J A Houmard1, M H Shinebarger, P L Dolan
1Department of Biochemistry, School of Medicine, East Carolina University, Greenville, North Carolina 27858.
The American Journal of Physiology
|June 1, 1993
Summary
Exercise training significantly boosts glucose transporter type 4 (GLUT-4) protein in middle-aged men, improving insulin sensitivity. This study shows exercise enhances key proteins for better glucose metabolism.
Area of Science:
- Exercise Physiology
- Metabolic Health
- Molecular Biology
Background:
- Middle-aged sedentary individuals often experience decreased insulin sensitivity.
- Glucose transporter type 4 (GLUT-4) is crucial for muscle glucose uptake.
- Exercise is known to influence metabolic parameters, but effects on GLUT-4 in this demographic require further investigation.
Purpose of the Study:
- To investigate the impact of 14 weeks of exercise training on GLUT-4 protein concentration in the skeletal muscle of previously sedentary middle-aged men.
- To assess changes in insulin sensitivity alongside alterations in GLUT-4 protein levels.
- To explore potential correlations between GLUT-4 expression, muscle fiber type, and mitochondrial enzyme activity.
Main Methods:
- A cohort of 13 sedentary middle-aged men (average age 47.2 years) underwent 14 weeks of exercise training.
- Muscle biopsies (lateral gastrocnemius) were collected pre- and post-training (48 hours after the final session) to measure GLUT-4 protein concentration.
- Insulin action was evaluated using the insulin sensitivity index (ISI) derived from the minimal model.
Main Results:
- Exercise training resulted in a significant 1.8-fold increase in skeletal muscle GLUT-4 protein concentration (P < 0.001).
- Insulin sensitivity index (ISI) demonstrated a twofold increase (P < 0.05) following the training intervention.
- A ~10% increase in GLUT-4-rich type IIa muscle fibers was observed (P < 0.01), alongside a 1.7-fold rise in citrate synthase activity (P < 0.001).
Conclusions:
- Fourteen weeks of exercise training effectively elevates GLUT-4 protein concentration in the skeletal muscle of middle-aged men.
- The observed increase in GLUT-4 and associated improvements in insulin sensitivity highlight the benefits of exercise for metabolic health in this population.
- Exercise-induced adaptations in muscle, including enhanced GLUT-4 expression and mitochondrial capacity, contribute to improved glucose regulation.