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1 School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom
2 Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas, United States; Surgery, University of Texas Medical Branch, Galveston, Texas, United States
3 Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas, United States; Preventive Medicine and Community Health, UTMB, Rt 1220, Galveston, Texas, 77550, United States
4 Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas, United States
5 Metabolism Unit, Shriners Hospitals for Children, Galveston, Texas, United States; Surgery, University of Texas Medcial Branch, Galveston, Texas, United States
* To whom correspondence should be addressed. E-mail: k.d.tipton{at}bham.ac.uk.
Timing of nutrient ingestion has been demonstrated to influence the anabolic response of muscle following exercise. Previously, we demonstrated that net amino acid uptake was greater when free essential amino acids plus carbohydrates were ingested prior to resistance exercise rather than following exercise. However, it is unclear if ingestion of whole proteins prior to exercise would stimulate a superior response compared to following exercise. This study was designed to examine the response of muscle protein balance to ingestion of whey proteins both prior to and following resistance exercise. Healthy volunteers were randomly assigned to one of two groups. A solution of whey proteins was consumed either immediately prior to exercise (PRE; n=8) or immediately following exercise (POST; n=9). Each subject performed 10 sets of 8 repetitions of leg extension exercise. Phenylalanine concentrations were measured in femoral arteriovenous samples to determine balance across the leg. Arterial amino acid concentrations were elevated by ~50% and net amino acid balance switched from negative to positive following ingestion of proteins at either time. Amino acid uptake was not significantly different between PRE and POST when calculated from the beginning of exercise (67±22 and 27±10 for PRE and POST, respectively) or from the ingestion of each drink (60±17 and 63±15 for PRE and POST, respectively). Thus, the response of net muscle protein balance to timing of intact protein ingestion does not respond as does that of the combination of free amino acids and carbohydrate.
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