Fig. 20. Length-isometric tetanus-tension relation for single twitch muscle fibers of frog. Line in full summarizes results obtained with improved length- control system devised by A. F. Huxley and colleagues. Degree of overlap between thick filaments (length 1.6) and thin filaments (length 1.05 including z-line) for various critical sarcomere lengths (lower scale) is also indicated. (Ramsey PW, Street SF: J Cell Comp Physiol 15:11, 1940.)