Cellular adaptation of the trapezius muscle in strength-trained athletes

The aim of this study was to elucidate the cellular events that occur in th e trapezius muscle following several years of strength training. In muscle biopsies from ten elite power lifters (PL) and six control subjects (C), se veral parameters were studied: cross-sectional area of muscle fibres, myosi n heavy chain composition (MHC) and capillary supply [capillaries around fi bres (CAF) and CAF/fibre area]. A method was also developed for counting th e number of myonuclei and satellite cell nuclei. The proportion of fibres e xpressing MHC IIA, the cross-sectional area of each fibre type and the numb er of myonuclei, satellite cells and fibres expressing markers for early my ogenesis were significantly higher in PL than in C (P<0.05). A significant correlation between the myonuclear number and the cross-sectional area was observed. Since myonuclei in mature muscle fibres are not able to divide, w e suggest that the incorporation of satellite cell nuclei into muscle fibre s resulted in the maintenance of a constant nuclear to cytoplasmic ratio. T he presence of small diameter fibres expressing markers for early myogenesi s indicates the formation of new muscle fibres.