The sarcomere length dependence of the rate of heat production during isometric tetanic contraction of frog muscles.

Heat production and force have been measured as a function of sarcomere length between 1.6 and 3.0 microns during isometric tetani at 0 degree C for two types of frog muscle: sartorius and extensor longus digiti iv (e.l.d. iv). Stable heat rate declines linearly with increasing sarcomere length above 2.20 microns for both e.l.d. iv and sartorius muscles. In sartorius muscle stable heat rate remains at or near its maximum value between 1.75 and 2.20 microns while force decreases. In e.l.d. iv muscle, both stable heat rate and force decline linearly as sarcomere length decreases below 2.20 microns.