Postexercise myofibrillar protein synthesis rates do not differ following 1.5 g essential amino acids compared with 15 and 20 g of whey protein in young females.

Optimal adaptation to resistance exercise requires maximal rates of myofibrillar protein synthesis (MyoPS), which can be achieved by postexercise consumption of >20 g of protein or ∼2 g of the essential amino acid (EAA) leucine. These nutritional recommendations are based on studies in males. The aim of the present study was to compare the postexercise MyoPS response to nutrition in young females. Twenty-eight healthy, females [age: 28 ± 8 yr; body mass index (BMI): 24 ± 3 kg/m²] received a primed-continuous infusion of l-[ring-²H₅]-phenylalanine and completed a bout of unilateral resistance exercise before ingesting a drink containing either 1.5 g EAA (n = 10), 15 g (n = 10), or 20 g (n = 8) whey protein, containing 0.6, 1.5, and 2.0 g leucine, respectively. Blood and muscle samples were collected pre- and postexercise and drink ingestion to assess MyoPS and gene expression. Drink ingestion increased plasma leucine concentrations following 15 and 20 g whey protein compared with 1.5 g EAA (P < 0.0001). Exercise and drink ingestion increased basal (0.060 ± 0.026, 0.063 ± 0.034, 0.051 ± 0.023%·h^-1) MyoPS rates between 0 and 2 h to 0.117 ± 0.028, 0.098 ± 0.051 and 0.116 ± 0.034%·h^-1 (P < 0.0001) and between 2 and 4 h to 0.110 ± 0.028, 0.074 ± 0.038, and 0.082 ± 0.061%·h^-1 (P = 0.008) for 1.5, 15, and 20 g drinks, respectively, with no differences observed between drinks (P = 0.416). The postexercise changes in muscle mRNA expression of genes involved in protein turnover, substrate utilization, remodeling, and inflammation did not differ between drinks (P > 0.050). Postexercise MyoPS did not differ following ingestion of 1.5, 15, and 20 g drinks, hence 0.6 g leucine may be sufficient to stimulate postexercise MyoPS in young females.NEW & NOTEWORTHY This study provides evidence that postexercise myofibrillar protein synthesis rates do not differ following the ingestion of 1.5 g of essential amino acids, 15 and 20 g of whey protein, containing 0.6, 1.5, and 2.0 g of leucine, respectively, in young females. Protein and leucine doses below current recommendations, >20 g of protein or ∼2 g leucine, may be sufficient to optimally stimulate myofibrillar protein synthesis in young females.