Introduction: 

Satellite cells (SC) are mononuclear stem cells of skeletal muscle which play an important role in the muscular adaptive response to exercise. The exact extent of SC involvement in structural und functional remodelling processes in response to endurance exercise induced stimuli has received much less attention. The aim of this study was to analyze the effect of load-dependent endurance exercise on the number of SC and myonuclei in skeletal muscle of 10 young male cyclists (17.3±0.5yr).

Methods: 

We investigated the training period (TP1, Nov-Feb), the competitive season (CS, Feb-Oct) and the following TP (TP2). After each period muscle biopsies were obtained from the vastus lateralis muscle. SC were labelled with a monoclonal Pax-7 antibody and myonuclear number was analysed from HE-cross-sections (7mm). The muscle fiber diameter was measured.

Results: 

The SC number per muscle fiber at the end of the CS (0.56±0.059) was significantly decreased towards TP1 (0.94±0.269) and TP2 (0.82±0.092; p<0.05). The analysis of myonuclear number illustrated an inverse pattern to the SC number. After CS, the number of nuclei/fiber was significantly increased (4.00±0.933) towards TP1 (1.75±0.727) and TP2 (1.75±0.184), while no changes of fiber diameter were observed.

Conclusions: 

SC content is affected strongly in response to load-dependent endurance exercise. A change of exercise regimen from TP to CS by a reduction of volume and increase of intensity leads to a significant decrease of SC and a massive addition of the myonuclear number. According to the unaltered fiber diameter this indicates an enormous DNA-recruitment.