Concomitant increases in myonuclear and satellite cell content in female trapezius muscle following strength training

A skeletal muscle fibre maintains its cytoplasmic volume by means of hundre ds of myonuclei distributed along its entire length. Therefore it is hypoth esised that changes in fibre zize would involve modifications in myonuclear number. In this study, we have examined whether 10 weeks of strength train ing can induce changes in the number of myonuclei and satellite cells in fe male trapezius muscles. Biopsies were taken pre- and posttraining from the upper part of the descending trapezius muscle of nine subjects. Muscle samp les were analysed for fibre area and myonuclear and satellite cell number u sing immunohisto-chemistry. There was a 36% increase in the cross-sectional area of muscle fibres, The hypertrophy of muscle fibres was accompanied by an approximately 70% increase in myonuclear number and a 46% increase in t he number of satellite cells. Myonuclei number was positively correlated to satellite cell number indicating that a muscle with an increased concentra tion of myonuclei will contain a correspondingly higher number of satellite cells. The acquisition of additional myonuclei appears to be required to s upport the enlargement of multinucleated muscle cells following 10 weeks of strength training. Increased satellite cell content suggests that mitotic divisions of satellite cells produced daughter cells that became satellite cells.