title: Dose-dependent responses of myofibrillar protein synthesis with beef ingestion are enhanced with resistance exercise in middle-aged men.
abstract: Aging impairs the sensitivity of skeletal muscle to anabolic stimuli, such as amino acids and resistance exercise. Beef is a nutrient-rich source of dietary protein capable of stimulating muscle protein synthesis (MPS) rates in older men at rest. To date, the dose-response of myofibrillar protein synthesis to graded ingestion of protein-rich foods, such as beef, has not been determined. We aimed to determine the dose-response of MPS with and without resistance exercise to graded doses of beef ingestion. Thirty-five middle-aged men (59 ± 2 years) ingested 0 g, 57 g (2 oz; 12 g protein), 113 g (4 oz; 24 g protein), or 170 g (6 oz; 36 g protein) of (15% fat) ground beef (n = 7 per group). Subjects performed a bout of unilateral resistance exercise to allow measurement of the fed state and the fed plus resistance exercise state within each dose. A primed constant infusion of l-[1-(13)C]leucine was initiated to measure leucine oxidation and of l-[ring-(13)C(6)]phenylalanine was initiated to measure myofibrillar MPS. Myofibrillar MPS was increased with ingestion of 170 g of beef to a greater extent than all other doses at rest and after resistance exercise. There was more leucine oxidation with ingestion of 113 g of beef than with 0 g and 57 g, and it increased further after ingestion of 170 g of beef (all p < 0.05). Ingestion of 170 g of beef protein is required to stimulate a rise in myofibrillar MPS over and above that seen with lower doses. An isolated bout of resistance exercise was potent in stimulating myofibrillar MPS, and acted additively with feeding.
authors: Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1, Canada.
authors: Meghann J
authors: MJ
authors: Robinson
authors: Nicholas A
authors: NA
authors: Burd
authors: Leigh
authors: L
authors: Breen
authors: Tracy
authors: T
authors: Rerecich
authors: Yifan
authors: Y
authors: Yang
authors: Amy J
authors: AJ
authors: Hector
authors: Steven K
authors: SK
authors: Baker
authors: Stuart M
authors: SM
authors: Phillips
mesh_terms: D000596:Amino Acids / Q000097:blood; D000818:Animals; D002417:Cattle; D015444:Exercise / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008297:Male; D008460:Meat / Q000032:analysis*; D008875:Middle Aged; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D009124:Muscle Proteins