ABSTRACT
The purpose of present study was to investigate the relationship between the increase of sarcomere length, sarcomere number and tetanic tension of the extensor digitorum longus muscles during postnatal growth in mice. The following results were obtained ; 1) The cross-sectional area, length of muscle and fiber length increased rapidly up to 7th week. 2) The sarcomere number increased up to 9 th week, 3) The tetanic tension per cross-sectional area decreased significantly in 7 th week, 4) The maximum value of sarcomere length which was obtained at middle region of the fiber correlated significantly with the tetanic tension per cross-sectional area (the correlation coefficient : r=-0.675) . These observations suggest that the local expansion of sarcomere length during postnatal growth affects the tension development.