Leucine kinetics in endurance-trained humans

Area of Science:

• Exercise Physiology
• Nutritional Biochemistry
• Metabolic Research

Background:

• Endurance training significantly impacts metabolic adaptations.
• Understanding amino acid kinetics is crucial for metabolic health.
• Leucine plays a key role in protein synthesis and energy metabolism.

Purpose of the Study:

• To compare whole-body leucine kinetics between endurance-trained and sedentary individuals.
• To investigate the relationship between leucine turnover, oxidation, and resting energy expenditure.
• To determine if increased protein turnover contributes to elevated energy expenditure in trained subjects.

Main Methods:

• Utilized a 6-hour primed, constant-rate infusion of L-[1-13C]leucine in trained (TRN) and sedentary (SED) subjects.
• Measured whole-body leucine turnover and oxidation using tracer dilution techniques.
• Quantified leucine oxidation by measuring 13C enrichment in expired CO2 combined with respiratory calorimetry.

Main Results:

• Whole-body leucine turnover was significantly greater in TRN subjects (98.3 ± 5.0 µmol·kg−1·h−1) compared to SED subjects (75.3 ± 4.2 µmol·kg−1·h−1).
• No significant difference was observed in leucine oxidation rates between TRN (13.1 ± 0.97 µmol·kg−1·h−1) and SED (11.5 ± 0.48 µmol·kg−1·h−1) groups.
• TRN subjects exhibited higher resting energy expenditures, correlating positively with protein turnover (R = 0.61, P = 0.05).

Conclusions:

• Endurance training leads to increased whole-body leucine and/or protein turnover.
• The heightened resting energy expenditure in endurance-trained individuals may be attributed to increased protein turnover.
• Elevated protein turnover represents a potential metabolic adaptation contributing to energy balance in athletes.