 The purpose of this study is to investigate mechanisms underlying the reduction in muscle quality the ratio between muscle strength and muscle size with aging, and to investigate how these factors are affected by strength training and protein supplementation. It is already established that muscle quality defined as the ratio between the strength and the size of a muscle is improved with strength training, even in frail elderly individuals. However, the relative contribution of factors such as activation level, fat infiltration, muscle architecture and single fiber function is unknown. The main focus of this study is to investigate the relationship between muscle quality and muscle protein breakdown, as insufficient degradation of proteins is hypothesized to negatively affect muscle quality. 