Differential satellite cell density of type I and II fibres with lifelong endurance running in old men

Abstract Aim To investigate the influence of lifelong endurance running on the satellite cell pool of type I and type II fibres in healthy human skeletal muscle. Methods Muscle biopsies were collected from 15 healthy old trained men ( O ‐ T r) who had been running 43 ± 16 (mean ± SD ) kilometres a week for 28 ± 9 years. Twelve age‐matched untrained men (O‐ U n) and a group of young trained and young untrained men were recruited for comparison. Frozen sections were immunohistochemically stained for P ax7, type I myosin and laminin, from which fibre area, the number of satellite cells, and the relationship between these variables were determined. Results In O ‐ U n and O ‐ T r, type II fibres were smaller and contained fewer satellite cells than type I fibres. However, when expressed relative to fibre area, the difference in satellite cell content between fibre types was eliminated in O ‐ T r, but not O ‐ U n. A strong positive relationship between fibre size and satellite cell content was detected in trained individuals. In line with a history of myofibre repair, a greater number of fibres with centrally located myonuclei were detected in O ‐ T r. Conclusion Lifelong endurance training (i) does not deplete the satellite cell pool and (ii) is associated with a similar density of satellite cells in type I and II fibres despite a failure to preserve the equal fibre type distribution of satellite cells observed in young individuals. Taken together, these data reveal a differential regulation of satellite cell content between fibre types, in young and old healthy men with dramatically different training histories.