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Title: Acute regulation of skeletal muscle protein metabolism by nutrients, exercise and hypoxia
Author: Etheridge, Timothy
ISNI:       0000 0004 2691 7060
Awarding Body: University of Brighton
Current Institution: University of Brighton
Date of Award: 2010
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Muscle mass adapts in response to changing functional and metabolic demands of the organism and its maintenance is important for movement, health and survival. However, many questions remain regarding the acute response of muscle to feeding, exercise and altered environmental conditions. Thus, the aim of the present thesis was to investigate how muscle responds to changes in these stimuli. The first experiment aimed to understand the temporal response of muscle protein metabolism to a single oral protein feed. Rates of myofibrillar protein synthesis (MPS) exhibited a biphasic response to an acute protein meal. Myofibrillar and sarcoplasmic protein synthesis increased ~3-fold by 90 min post-feed before returning to postabsorptive values by 180 min, despite continued availability of amino acids. Phosphorylation (activation) of components of anabolic signalling mirrored the increase in MPS (e.g. p70S6K and 4EBP1 increased +2.1±0.2 and +2.6±0.5-fold, respectively), and remained elevated after MPS had declined to baseline. The second study assessed recovery of muscle function following delayed onset muscle soreness (DOMS)-inducing exercise when combined with an oral protein meal. Muscle force and power recovery was accelerated by 48 h post-exercise with protein ingestion vs. placebo (muscle force = -0.25% vs. -10.7%; power = -0.15% vs. -8.7% for protein and placebo trials, respectively). The augmented functional recovery was not, however, matched by improvements in perceived muscle soreness or plasma markers of damage. Finally, the third study examined the response of MPS to reduced O2 supply (hypoxia, 12.5% O2). After 3.5 h hypoxia at rest, MPS was unaffected from normoxic values. However, although MPS increased after normoxic resistance exercise (+224±49%), this was blunted during hypoxia (+184±268%, p > 0.05) despite increased anabolic signalling (p70S6K and ACC-β changing +3.4±1.1-fold and -0.7±0.1-fold, respectively), and was correlated with the measured blood O2 saturation (r2 = 0.48, p < 0.05). It is concluded that (i) after a single oral protein feed, muscle protein synthesis demonstrates a 'muscle-full' effect where, following rapid activation, MPS is switched-off despite continued elevated amino acid concentrations and anabolic signalling, (ii) a single post-exercise protein meal increases muscle function recovery, but not perceived muscle soreness or blood markers of damage, and (iii) reduced muscle O2 supply suppresses protein synthesis after exercise, even in the presence of increased anabolic signalling. These findings have significant implications for both athletic and clinical populations in terms of nutritional and exercise strategies employed, and for the efficacy of exercise regimens for increasing/maintaining muscle mass in conditions of reduced O2 supply.
Supervisor: Watt, Peter ; Maxwell, Neil Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: B120 Physiology