Repeated Prolonged Exercise Decreases Maximal Fat Oxidation in Older Men

Area of Science:

• Exercise Physiology
• Metabolic Adaptation
• Aging Research

Background:

• Understanding how prolonged exercise impacts fat metabolism and muscle adaptation in older adults is crucial for optimizing training and health.
• Previous research has focused on younger populations, leaving a gap in knowledge regarding the specific responses of older, trained individuals.

Purpose of the Study:

• To investigate the effects of repeated prolonged exercise on fat metabolism and muscle adaptation in older trained men.
• To assess changes in maximal oxygen uptake (V˙O2max) and maximal fat oxidation rates following extensive cycling.

Main Methods:

• Six older trained men (61 ± 4 yr) completed 14 days of prolonged cycling (2706 km).
• Measurements included V˙O2max, maximal fat oxidation, plasma free fatty acid and glucose concentrations, and muscle biopsies.
• Muscle tissue analysis assessed enzyme activities and protein expression related to glucose and lipid metabolism.

Main Results:

• Maximal fat oxidation rate decreased significantly (32% ± 8%), while V˙O2max showed a smaller decrease (6% ± 2%).
• Plasma free fatty acid availability was reduced, but muscle adaptations included increased expression of glucose transporters (GLUT4) and lipolytic enzymes.
• Muscle glycogen and triacylglycerol content remained unchanged.

Conclusions:

• The decline in maximal fat oxidation is likely linked to reduced exogenous fatty acid supply.
• Muscle adaptations indicate an enhanced capacity for glucose uptake and endogenous lipid mobilization, shifting fuel utilization during exercise.
• These findings suggest a complex interplay between substrate availability and muscle plasticity in older athletes.