Twenty years ago Carlson and Faulkner (1989) made the interesting observation that if a muscle from an aged rat was transplanted into a young host the recovery potential of that muscle, in terms of mass and force production, was similar to that of a transplanted young muscle. Conversely, both young and old muscles recovered less well if they were transplanted into an aged as opposed to young host. This study provided the first evidence of a negative age-related effect of the systemic environment on skeletal muscle. More recently these observations have been supported by work on parobiotic mice, animals which share a conjoined circulation. Using this model, recovery to a damaged older muscle was markedly improved if the aged animal shared its circulation with a younger animal (Conboy et al. 2005). Recent studies (Carlson et al. 2008) suggest that this age-related impairment to recovery from damage relates to changes in a number of signalling pathways (Notch, TGF-beta, pSmad3). These pathways regulate the proliferation and the myogenic commitment of satellite cells. Satellite cells are the muscle’s stem cells, which are juxtaposed to muscle fibres and are required not only for repair, but also for adaptation and hypertrophy. Whilst age-related impairments in the recovery of muscle from damage have been demonstrated in rodent studies, human exercise studies have shown that even the muscles of very elderly people are very able to increase satellite cell number and hypertrophy in response to overload. We have recently used a primary cell / serum model to study the effects of the age of systemic environment on the behaviour of human cells extracted from muscle biopsies in culture. We have shown that committed myoblasts show similar abilities to both proliferate and differentiate when cultured in either a young or old serum (George et al. 2008). Furthermore, the cell itself (i.e. whether it originates from a young or elderly donor) shows no age-dependent behaviour. These findings would therefore suggest that a sufficient number of satellite cells are able to successfully progress through the myogenic lineage and can contribute to adaptation, even in an apparently hostile aged milieu.