Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion

Metabolism Unit, Shriners Hospitals for Children, Galveston 77550; and Department of Surgery, The University of Texas Medical Branch, Galveston, Texas 77555 The purpose of this study was to determine if the acute anabolic muscle response to resistance exercise and essential amino acids (EAA) reflects the response over 24 h. Seven subjects participated in the following two 24-h studies: 1 ) resting (REST) and 2 ) rest plus resistance exercise and consumption of EAA (ES). Net balance (NB) across the leg was determined for four amino acids. [ 13 C 6 ]phenylalanine was infused to determine mixed muscle fractional synthetic rate (FSR). Twenty-four-hour FSR was significantly greater for ES than for REST ( P = 0.003). Exchange of phenylalanine across the leg was 194 ± 74 (SE) mg for ES and 371 ± 88 mg for REST ( P = 0.07) over 24 h and 229 ± 42 mg (ES) and 28 ± 15 mg (REST; P