The energy supply characteristics of L-leucine in endurance sports

As a core member of branched-chain amino acids (BCAAs), L-leucine differs from traditional energy substrates such as carbohydrates and fats in its energy supply characteristics during endurance exercise. Centered on "targeted energy supply and synergistic metabolic regulation," it not only directly participates in energy metabolism but also indirectly supports endurance performance through regulating physiological mechanisms. Its core characteristics are as follows:

I. Direct Energy Supply Mechanisms and Characteristics

Energy Supply Pathway and Proportion: During endurance exercise (duration > 60 minutes, intensity 55%~75% VO₂max), L-leucine undergoes oxidative energy supply through the pathway of "transamination → ketoacid dehydrogenation → tricarboxylic acid cycle," accounting for approximately 5%~10% of total energy supply. With prolonged exercise duration (e.g., ultra-marathon), this proportion can increase to 12%~15%, making it an important supplementary energy source alongside fats and carbohydrates.

Muscle-Targeted Energy Supply: L-leucine can be directly absorbed and utilized by skeletal muscle without prior metabolic conversion in the liver. It has a high oxidation rate (2~3 times higher than aromatic amino acids), enabling rapid ATP production for working muscles and alleviating energy deficit during prolonged exercise.

Anti-Fatigue Energy Supply Advantage: Unlike carbohydrates that rely on glycogen stores, L-leucine can be continuously obtained through minimal mobilization of intramuscular protein breakdown or exogenous supplementation. During the glycogen depletion phase (e.g., 90 minutes after exercise initiation), its energy supply proportion increases significantly, delaying the onset of the "glycogen wall."

II. Metabolic Regulation Characteristics for Indirect Endurance Support

Glycogen Sparing and Promotion of Fat Breakdown: L-leucine inhibits the rate of intramuscular glycogen breakdown while activating lipase activity in adipose tissue, promoting fatty acid oxidative energy supply. This reduces carbohydrate consumption, extends the utilization time of glycogen stores, and enhances the upper limit of exercise endurance.

Regulation of Branched-Chain Amino Acid Oxidation Balance: During endurance exercise, L-leucine acts synergistically with L-isoleucine and L-valine. By competing for branched-chain amino acid transaminase (BCAT), it regulates the oxidation ratio of the three amino acids, avoiding excessive consumption of a single amino acid, maintaining the stability of the intramuscular amino acid pool, and reducing the accumulation of fatigue-related metabolites (e.g., ammonia).

Muscle Tissue Protection and Reduction of Energy Waste: L-leucine activates the mTOR signaling pathway to promote muscle protein synthesis while inhibiting exercise-induced muscle protein breakdown, reducing muscle tissue loss. Maintenance of muscle mass improves basal metabolic efficiency and avoids energy metabolism disorders caused by muscle damage, indirectly supporting long-term endurance training adaptation.

III. Supplementation and Application Characteristics

Synergistic Energy Supply Effect of Exogenous Supplementation: Exogenous supplementation of L-leucine 30~60 minutes before endurance exercise or continuously during exercise (single dose: 0.5~1.0 g/h; optimal when compounded with other BCAAs at a ratio of 2:1:1) can directly increase the concentration of energy substrates in muscle, delay fatigue onset, and improve exercise endurance by 10%~20% (e.g., extending running time by 15~30 minutes).

Metabolic Compatibility and Safety: Oxidation of L-leucine does not produce fatigue-inducing substances such as lactic acid. Its metabolites (ketoacids, CO₂, water) are easily excreted from the body without increasing metabolic burden. Additionally, its energy supply process is insulin-independent, making it suitable for scenarios with blood glucose fluctuations during exercise without the risk of hypoglycemia.

Synergy with Other Energy Substrates: When compounded with carbohydrates (e.g., glucose), L-leucine promotes glycogen synthesis and absorption, improving energy supply efficiency. When combined with medium-chain triglycerides (MCT), it forms a dual energy supply system of "amino acids + fats," further optimizing endurance performance.

L-leucine's energy supply during endurance exercise is centered on "direct targeted energy supply + indirect metabolic regulation." It not only acts as an energy supplementary substrate to alleviate energy deficit but also extends endurance limits through mechanisms such as glycogen sparing, muscle protection, and metabolic balance. As a key nutrient in endurance sports nutrition supplementation, it possesses dual values of energy supply and functional regulation.