Fig. 8. The influence of maintenance temperature of frogs on the enhancement of twitch force by stretch. Frogs were kept at room temperature (22°C, open circles) or at 4°C (filled circles) for more than 2 months and twitch forces were measured at low temperature (4°C) in both cases. Forces were measured 2 min after stretching a muscle from l₀ to the length indicated on the abscissa. The data points (open circles) are the same as those shown in Fig. 6. Twitch forces are expressed as values relative to the force at resting length (l₀) by direct stimulation. The thick line shows the regression curve of the twitch force induced by direct stimulation as shown in Fig. 5A.