L-leucine used in combination with carbohydrates

Combined supplementation of L-leucine and carbohydrates significantly enhances endurance exercise performance (extending exercise time by 10%–20%) and delays fatigue through synergistic effects of "complementary energy supply, accelerated glycogen synthesis, and enhanced muscle protection." It outperforms sole supplementation of carbohydrates or L-leucine, serving as a highly effective nutritional support strategy for endurance exercise.

I. Synergistic Mechanisms of Action

1. Complementary Energy Supply to Extend Durability

Carbohydrates (glycogen, glucose) are the primary energy source for endurance exercise, rapidly catabolized to meet energy demands during the early and middle phases of exercise.

As the most energy-efficient branched-chain amino acid, L-leucine’s oxidative energy supply rate increases 3–5 times when muscle glycogen is depleted in the late phase of exercise (after 60 minutes), accounting for 10%–15% of total energy. This compensates for insufficient carbohydrate energy and delays fatigue caused by energy shortage.

2. Promote Glycogen Synthesis and Storage to Boost Energy Reserves

Carbohydrates directly replenish muscle glycogen, while L-leucine activates the insulin signaling pathway, improves insulin sensitivity, facilitates glucose transport into muscle cells, and accelerates glycogen resynthesis.

After combined supplementation, post-exercise muscle glycogen recovery rate is 25%–30% higher than that of sole carbohydrate supplementation. This stores more energy for subsequent endurance exercise and reduces fatigue accumulation during repeated training.

3. Inhibit Muscle Breakdown to Protect Exercise Capacity

Prolonged endurance exercise easily activates muscle protein-degrading enzymes due to energy shortage and stress, leading to muscle loss and reduced strength.

L-leucine activates the mTOR signaling pathway and inhibits the ubiquitin-proteasome system to reduce muscle protein degradation. Meanwhile, carbohydrates maintain stable blood glucose, preventing muscle protein from being catabolized for energy. Together, they synergistically protect muscle function and maintain muscle strength and output efficiency during endurance exercise.

4. Alleviate Central Fatigue to Improve Performance

In the late phase of endurance exercise, increased tryptophan entry into the brain triggers central fatigue.

L-leucine competes with tryptophan for blood-brain barrier transport channels; combined supplementation reduces tryptophan entry into the brain. Simultaneously, carbohydrates maintain blood glucose to avoid cerebral energy deficiency, synergistically alleviating central fatigue and extending exercise duration.

II. Combined Supplementation Plans for Different Scenarios

1. Prolonged Endurance Exercise (Marathon, Long-Distance Cycling, >90 Minutes)

Supplementation Timing & Dosage:

60 minutes before exercise: 2–3g L-leucine + 50–60g complex carbohydrates (oats, whole-wheat bread) for slow energy release and preloading glycogen/amino acid reserves.

During exercise (every 60 minutes): 1–1.5g L-leucine + 30–40g rapidly absorbed carbohydrates (sports drinks, energy gels) to continuously supplement energy and inhibit muscle breakdown/central fatigue.

Within 30 minutes after exercise: 2–3g L-leucine + 40–50g carbohydrates (glucose, maltodextrin) for rapid glycogen recovery and muscle repair.

Effect: Exercise endurance extends by 15%–20%, muscle weakness in the late phase is reduced, and post-race recovery is shortened by 1–2 days.

2. Moderate-Intensity Endurance Exercise (Jogging, Swimming, 60–90 Minutes)

Supplementation Timing & Dosage:

30 minutes before exercise: 1.5–2g L-leucine + 30–40g carbohydrates (banana, energy bar) to rapidly activate energy metabolism.

During exercise (every 75 minutes): 1g L-leucine + 20–30g carbohydrates (sports drinks) to maintain energy and amino acid levels.

After exercise: 1.5–2g L-leucine + 30g carbohydrates to promote recovery.

Effect: Fatigue onset is delayed, exercise completion quality improves, and heart rate recovery accelerates.

3. High-Frequency Endurance Training (1 Session/Day, 3–5 Consecutive Days)

Supplementation Timing & Dosage:

30 minutes before training: 1–1.5g L-leucine + 20–30g carbohydrates to meet the energy needs of a single training session.

Within 1 hour after training: 1.5–2g L-leucine + 30–40g carbohydrates to accelerate glycogen and muscle recovery and avoid cumulative fatigue.

Effect: Endurance levels remain stable without significant decline during consecutive training, muscle soreness is reduced, and training adherence improves.

III. Supplementation Precautions & Optimization Suggestions

1. Ratio and Dose Control

The optimal mass ratio of L-leucine to carbohydrates is 1:15–1:20. Avoid excessive L-leucine (single dose >2g) to prevent gastrointestinal discomfort, or insufficient carbohydrates that compromise energy supply.

Daily total dose: L-leucine ≤8g; carbohydrates adjusted according to exercise expenditure (usually 5–7g/kg body weight per day).

2. Selection of Carbohydrate Types

Prioritize rapidly absorbed carbohydrates (glucose, maltodextrin) before and after exercise to accelerate absorption and utilization. For long pre-exercise periods (>60 minutes), combine with complex carbohydrates to maintain stable blood glucose.

Avoid high-fiber, high-fat carbohydrates (e.g., whole-wheat crackers + nuts) to prevent delayed digestion and exercise-induced bloating.

3. Adjustments for Special Populations

Endurance athletes in fat-loss periods: Appropriately increase L-leucine dose (2–3g post-exercise) to strengthen muscle protection, while controlling total carbohydrate intake (3–4g/kg body weight per day) to avoid caloric surplus.

Diabetic patients: Monitor blood glucose during supplementation, select low-glycemic index carbohydrates (e.g., oats, mixed beans), and avoid sharp blood glucose fluctuations.