Effect of ambient temperature on protein breakdown during prolonged exercise

Area of Science:

• Exercise Physiology
• Environmental Stress
• Human Metabolism

Background:

• Understanding how environmental temperature impacts physiological responses during exercise is crucial for optimizing athletic performance and health.
• Previous research indicates hormonal changes during exercise, but the specific role of ambient temperature on protein metabolism requires further elucidation.

Purpose of the Study:

• To investigate the effect of different ambient temperatures (5, 20, and 30°C) on protein utilization during prolonged cycling exercise in male subjects.
• To examine the relationship between environmental temperature, hormonal responses (norepinephrine, epinephrine, cortisol), and metabolic markers (glucose, FFA, lactic acid).

Main Methods:

• Eight male subjects performed 90-minute cycling sessions at 5, 20, and 30°C.
• Measurements included core and skin temperatures, oxygen consumption, respiratory exchange ratio, and venous concentrations of key metabolites and hormones.
• Urea nitrogen excretion was assessed in urine and sweat over 72 hours to calculate protein utilization.

Main Results:

• Protein utilization was significantly higher in 5°C (86.9 g) and 20°C (82.9 g) compared to 30°C (34.0 g).
• Ambient temperature influenced catabolic hormone levels, with norepinephrine, epinephrine, and cortisol being highest in 5°C and lowest in 20°C.
• Core body temperature (Tre) and oxygen consumption (VO2) were highest in the 30°C environment, while venous free fatty acid (FFA) was higher and lactic acid (LA) was greater in 5°C and 30°C, respectively.

Conclusions:

• Exercise protein breakdown is significantly affected by ambient temperature, independent of circulating catabolic hormones alone.
• Alterations in carbohydrate and fat metabolism, indicated by changes in FFA and LA concentrations across temperatures, likely contribute to the observed variations in protein utilization during exercise.