Fig. 3. The effect of temperature is different for the two muscles tested in vitro. Values are means ± s.e.m. (N=6). (A) Time (ms) needed to reach peak force in a tetanic stimulation increases significantly (over sixfold) as temperature decreased from 40°C to 20°C. Note also how the jaw closer muscle (m. adductor mandibulae externus superficialis posterior) is markedly faster than the femur retractor (m. caudofemoralis) at all temperatures. (B) Relative tetanic force as a function of temperature. Note how the peak force delivered by the jaw muscle is nearly independent of temperature (filled circles) whereas a notable optimum in force production appears to be present for the femur retractor (35°C; open circles).