Abstract
This study was designed to better understand the molecular mechanisms involved in the anabolic resistance observed in elderly people. Nine young (22 ± 0.1 years) and 10 older (69 ± 1.7 years) volunteers performed a one-leg extension exercise consisting of 10 × 10 repetitions at 70% of their 3-RM, immediately after which they ingested 30 g of whey protein. Muscle biopsies were taken from the vastus lateralis at rest in the fasted state and 30 min after protein ingestion in the non-exercised (Pro) and exercised (Pro+ex) legs. Plasma insulin levels were determined at the same time points. No age difference was measured in fasting insulin levels but the older subjects had a 50% higher concentration than the young subjects in the fed state (p < 0.05). While no difference was observed in the fasted state, in response to exercise and protein ingestion, the phosphorylation state of PKB (p < 0.05 in Pro and Pro+ex) and S6K1 (p = 0.059 in Pro; p = 0.066 in Pro+ex) was lower in the older subjects compared with the young subjects. After Pro+ex, REDD1 expression tended to be higher (p = 0.087) in the older group while AMPK phosphorylation was not modified by any condition. In conclusion, we show that the activation of the mTORC1 pathway is reduced in skeletal muscle of older subjects after resistance exercise and protein ingestion compared with young subjects, which could be partially due to an increased expression of REDD1 and an impaired anabolic sensitivity.
Highlights
Sarcopenia has been defined as the decline in skeletal muscle mass and strength with advancing age [1]
The protein-rich drink and exercise increased blood glucose (p < 0.001) and plasma insulin (p < 0.01), leucine (p < 0.001), isoleucine (p < 0.001), and valine (p < 0.001) concentrations in both young and old subjects compared to the fasted conditions (Table 3)
Insulin increased about four times between Fasted and protein ingestion in the non-exercised (Pro)+ex in the older compared with 2.5 times in the young subjects, resulting in a higher plasma insulin concentration in the older compared with the young group (p < 0.05)
Summary
Sarcopenia has been defined as the decline in skeletal muscle mass and strength with advancing age [1]. Resistance exercise and adequate protein-based nutrition are the current most effective means to limit the loss of muscle mass with aging [3]. The benefits of exercise and nutritional interventions to counteract sarcopenia may be partially reduced by a blunted responsiveness to these stimuli [4,5]. This phenomenon has been termed “anabolic resistance” to reflect the inability of the muscle to maintain its protein mass by appropriate stimulation of protein synthesis, a major mechanism contributing to sarcopenia [6].
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