Does the muscle protein synthetic response to exercise and amino acid-based nutrition diminish with advancing age? A systematic review

Our aim was to assess whether the muscle protein synthesis (MPS) response to acute exercise and/or amino acid-based nutrition is attenuated in older compared with young individuals. A systematic review was conducted on studies that directly examined the influence of age on the MPS response to exercise and/or amino acid-based nutrition. Each study arm was synthesised and reported as providing sufficient or insufficient 'evidence of age-related muscle anabolic resistance'. Subsequently, three models were established to compare age-related differences in the MPS response to different anabolic stimuli. Following exercise alone, 8 of the 17 study arms provided sufficient 'evidence of age-related muscle anabolic resistance'. In response to amino acid-based nutrition, 8 of the 21 study arms provided sufficient 'evidence of age-related muscle anabolic resistance'. When exercise and amino acid-based nutrition were combined, only 2 of the 10 study arms provided sufficient 'evidence of age-related muscle anabolic resistance'. Our results highlight that optimisation of exercise and amino acid-based nutrition is sufficient to overcome age-related muscle anabolic resistance. However, the exercise volume and/or the amino acid/protein dose and leucine content must exceed a certain threshold to stimulate equivalent MPS rates in young and older adults, below which age-related muscle anabolic resistance may manifest.