Ingesting a leucine-enriched essential amino acid and carbohydrate solution 1 hour after resistance exercise in young, untrained men increases muscle protein synthesis by 145% above baseline, whereas resistance exercise alone increases muscle protein synthesis by only 41%, indicating a synergistic effect between nutrient intake and resistance training.

After a workout, drinking a shake with leucine and sugar causes leucine to directly trigger a cellular switch called mTOR, while the sugar raises insulin levels, which also activates mTOR. When both signals are present, mTOR turns on strongly and tells the cell’s protein-making machines to start working faster. This leads to more building blocks being stitched together into new muscle proteins, making muscle growth much stronger than from exercise alone.