The main drivers for skeletal muscle protein synthesis in humans are both dietary and exercise related. Increasing the energy and protein content of the diet, as well as performing resistance training exercise can stimulate the anabolic environment necessary for muscle protein synthesis. The balance between muscle protein synthesis and breakdown is not static and can be effected by a number of factors, particularly age. As ageing occurs, protein synthesis rates tend to fall with the result that muscle mass decreases as the balance shifts towards breakdown. This age related decline in muscle is termed sarcopaenia and its cause is essentially unknown. Although it is known that increased physical activity and improved diet are able to improve body composition in the elderly, it is not known if sarcopaenia is contributed to by an inevitable decline in the response of protein synthesis to exercise and diet.
Researchers1 attempted to further understand sarcopaenia by comparing the protein digestion and absorption kinetics, and the subsequent protein synthetic rates, between elderly and young subjects following exercise as well as at rest. The data showed that following consumption of 20grams of protein, both young and elderly subjects displayed similar rates of protein appearance in plasma suggesting that absorption of protein was not impaired with age. There was also no difference between the appearance of protein in the plasma at rest or after exercise. Muscle protein synthesis rates did not differ significantly between the elderly and young subjects at rest or following exercise, suggesting no impairment of protein synthesis with age. However, those who performed exercise before consumption of protein (both young and old) displayed increased protein synthesis rates. These results suggest that exercise and protein stimulated skeletal muscle protein synthesis do not diminish with age.
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