After strenuous endurance exercise, the intake of protein leucine can accelerate the synthesis of muscle protein and promote the recovery of muscle performance. The aim of this study was to investigate whether low-dose protein leucine mixture can increase skeletal muscle myofibrillar protein synthesis fraction (FSR) after endurance exercise.
In a cross-over design experiment, 12 subjects completed 100 minutes of intensive cycling training. In the first 90 minutes of the 240 minute recovery period, they were randomly divided into four groups: 70 / 15 / 180 / 30 g protein / leucine / carbohydrate / fat, 23 / 5 / 180 / 30 g 5leu, or 0 / 0 / 274 / 30 g control drink. FSR was detected by L-phenylalanine method, and the phosphorylation of mTORC1 signaling pathway was detected by Western blot.
Results: the FSR of 5leu group increased by 33%, which was close to the maximum value of FSR activation. The dose of protein leucine increased FSR by 3 times. Although FSR results were similar, the phosphorylation level of mTORC1 increased only at 15 Leu for 30 min, but increased at one or both time points in the amount of protein leucine. The plasma leucine and essential amino acids concentrations in the control group decreased during the recovery process, but increased with the increase of protein leucine dose. The serum insulin level in 15 Leu group was higher than that in control group, but there was no significant difference compared with 5 Leu group. Regression analysis showed that the phosphorylation of p70s6k-rps6 was in accordance with FSR, but there was little correlation between plasma leucine and essential amino acids.
After endurance exercise, 23 grams of protein containing 5 grams of leucine can reach the maximum value of FSR, which may be attributed to mtorc1-s6k-rps6 signal, insulin, or amino acids. The effect of leucine amount of translation protein on protein synthesis to optimize adaptation and muscle level needs further study.