Prevalence of sarcopenia is up to 60% of those individuals over 80 years of age and is associated with increased disability. The causes behind the age-related loss of muscle are difficult to discern. Measurements of protein synthesis/breakdown and net protein balance are important, and further methodological development is warranted. Whole body protein turnover is changed only little - if at all - with ageing, when corrected for fat free mass of the individuals. Discrepancies in reports are often related to inconsistent recordings of energy intake especially protein and variation in subject, gender and physical activity level. Ageing is associated with reduced sensitivity toward amino acids, increased first pass uptake in a splanchnic region and a reduced postprandial stimulation of protein synthesis. Physical activity and amino acids are additive in effect also in elderly individuals, and timing of training and protein intake is crucial, in that early intake of amino acids is advantageous with regards to stimulation of protein synthesis.