Mechanisms of, and countermeasures to, age-related muscle anabolic resistance and sarcopenia

Sarcopenia negatively impacts physical function and health. Although the mechanisms underpinning sarcopenia are unclear, a blunted response to anabolic stimuli is observed. Accordingly, Chapter 2 explored how dose, timing, distribution and source of dietary protein intake differed between healthy young and older individuals. We showed that, whilst the recommended dietary allowance for protein was met by most individuals, total protein intake was lower and unevenly distributed across meals in old. The observation of sub-optimal protein intakes in older individuals has important implications for skeletal muscle maintenance. Therefore, in Chapter 3 we investigated the muscle anabolic response in young lean, old lean and obese old individuals to a suboptimal protein dose. Whilst young lean and, to a lesser extent, old lean significantly increased postprandial myofibrillar protein synthesis (MyoPS), this response was blunted in obese old. Furthermore, MyoPS correlated significantly with step count and leg fat mass in old. Based on the age-related decrease in MyoPS, we assessed the ability of phosphatidic acid (PA) to increase MyoPS at rest and after exercise in Chapter 4. Compared to a placebo treatment, MyoPS was blunted upon PA consumption in the late phase of resistance exercise recovery and was probably due to impaired anabolic signaling.