Native whey- and milk-protein supplementation combined with resistance exercise, induces similar anabolic signaling-responses downstream of mTOR in elderly
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Background: Reduced muscle mass seen with age, often referred to as age-related atrophy or sarcopenia, has negative effects on physical function. There are frequent reports of a blunted anabolic response in elderly to both resistance exercise (RE) and protein intake, and this is referred to as anabolic resistance. Translation initiation and elongation signaling responses after a single exposure of RE and protein intake is often used as indexes of anabolic responsiveness. Aim: To examine whether habitual intake of un-denatured and specially filtrated native whey (NW) with a faster absorption-rate and higher leucine content than milk, would lead to greater hypertrophy and 1RM strength-gains after 11 weeks of resistance training, mirrored by increased anabolic signaling. Methods: Two groups of elderly (total of 9 men and 7 women), mean age 73 years completed a 10RM whole-body workout combined with intake of 20 g NW- or milk-protein before (acute 1) and after (acute 2) 11 weeks of strength training. Muscle biopsies were collected from m. vastus lateralis pre- and 2 hour post-exercise. Tissue samples were analyzed for total protein- and phosphorylated levels of p706SK, 4E-BP1 and eEF2. Results: The ratio of phosphorylated/total p706SK increased significantly on acute 2, and with a strong tendency on acute 1. Ratio of phosphorylated/total 4E-BP1 and eEF2 remained unchanged from baseline in both groups on acute 1 and 2. There was no differences (P>0.05) in any of the studied signaling proteins within each group, or between groups on either acute day. Both groups experienced similar increases in m. vastus lateralis thickness (+6-7%), lean body mass (2.1-2.3 kg) and 1RM strength (+20-40%). Phosphorylation patterns of our studied signaling proteins 2 hours post- RE and -protein intake were not correlated to any long-term outcome measure on an individual level. Discussion and conclusion: The difference in leucine-content between NW and milk might have been too small to detect differences between our groups. Supplementation with equal amounts of protein from NW and milk resulted in similar signaling for muscle hypertrophy and similar gains in m. vastus lateralis muscle thickness, muscle mass and muscle strength. Our findings emphasize that acute measures of intracellular anabolic signaling responses downstream of mTORC1 should be interpreted with caution if used as indexes of responsiveness to repeated RE and protein intake.
Masteroppgave - Norges idrettshøgskole, 2015