Effects of reduced ambient temperature on fat utilization during submaximal exercise

Area of Science:

• Exercise Physiology
• Environmental Physiology
• Metabolic Studies

Background:

• Understanding fuel utilization during exercise in varying environmental conditions is crucial for athletic performance and health.
• Cold exposure is known to affect physiological responses, but its specific impact on substrate oxidation during prolonged exercise requires detailed investigation.

Purpose of the Study:

• To investigate the influence of cold air exposure on fuel utilization during prolonged cycling exercise.
• To determine how different ambient temperatures affect substrate oxidation rates and related metabolic markers.

Main Methods:

• Nine male subjects performed 90-minute cycling trials at -10°C, 0°C, 10°C, and 20°C with constant external work.
• Oxygen consumption (VO2) and respiratory exchange ratio (RER) were measured to assess fuel utilization.
• Blood samples were analyzed for glycerol and glucose concentrations, and plasma epinephrine and norepinephrine levels were determined.

Main Results:

• Fat oxidation rates were significantly lower at -10°C and 0°C compared to 10°C and 20°C.
• Respiratory exchange ratio was higher in colder conditions (-10°C, 0°C), indicating a greater reliance on carbohydrate oxidation.
• Blood glycerol and glucose concentrations were lower in the coldest trial (-10°C) compared to the 20°C trial, while plasma epinephrine was higher at 20°C.

Conclusions:

• Cold air exposure diminishes fat oxidation during prolonged cycling exercise.
• This reduction in fat utilization may be due to decreased lipolysis, reduced free fatty acid mobilization, or impaired muscle oxidative capacity.
• The findings highlight the impact of cold environments on metabolic responses during endurance exercise.