Maintaining muscle mass and function is important in healthy ageing to maintain quality of life. Loss of muscle mass is major problem, as beyond the age ~50, muscle mass declines by ~1-2% a year. To prevent this loss, the investigators need to understand the mechanism regulating muscle mass as we age. In this project the investigators aim to determine these mechanisms using a new technique of heavy water ingestion, this allows measurement of multiple aspects of skeletal muscle mass metabolism e.g. protein synthesis, over long periods (6 weeks) as people go about their normal everyday activities. The investigators also aim to determine the influence of resistance exercise training on older muscle, as well as differences between men and women in muscle responses to exercise and nutrition HMB (beta-hydroxy-beta-methylbutyrate).