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Appears in Collections:Faculty of Health Sciences and Sport Journal Articles
Peer Review Status: Refereed
Title: Mixed muscle protein synthesis and breakdown after resistance exercise in humans
Author(s): Phillips, Stuart M
Tipton, Kevin
Aarsland, Asle A
Wolf, Steven E
Wolfe, Robert R
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Keywords: hypertrophy
muscle damage
fractional synthetic rate
fractional breakdown rate
Isometric exercise
Issue Date: Jul-1997
Date Deposited: 22-Aug-2012
Citation: Phillips SM, Tipton K, Aarsland AA, Wolf SE & Wolfe RR (1997) Mixed muscle protein synthesis and breakdown after resistance exercise in humans. American Journal of Physiology - Endocrinology and Metabolism, 273 (1), pp. E99-E107.
Abstract: Mixed muscle protein fractional synthesis rate (FSR) and fractional breakdown rate (FBR) were examined after an isolated bout of either concentric or eccentric resistance exercise. Subjects were eight untrained volunteers (4 males, 4 females). Mixed muscle protein FSR and FBR were determined using primed constant infusions of [2H5]phenylalanine and 15N-phenylalanine, respectively. Subjects were studied in the fasted state on four occasions: at rest and 3, 24, and 48 h after a resistance exercise bout. Exercise was eight sets of eight concentric or eccentric repetitions at 80% of each subject's concentric 1 repetition maximum. There was no significant difference between contraction types for either FSR, FBR, or net balance (FSR minus FBR). Exercise resulted in significant increases above rest in muscle FSR at all times: 3 h = 112%, 24 h = 65%, 48 h = 34% (P less than 0.01). Muscle FBR was also increased by exercise at 3 h (31%; P less than 0.05) and 24 h (18%; P less than 0.05) postexercise but returned to resting levels by 48 h. Muscle net balance was significantly increased after exercise at all time points [(in %/h) rest = -0.0573 +/- 0.003 (SE), 3 h = -0.0298 +/- 0.003, 24 h = -0.0413 +/- 0.004, and 48 h = -0.0440 +/- 0.005], and was significantly different from zero at all time points (P less than 0.05). There was also a significant correlation between FSR and FBR (r = 0.88, P less than 0.001). We conclude that exercise resulted in an increase in muscle net protein balance that persisted for up to 48 h after the exercise bout and was unrelated to the type of muscle contraction performed.
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