Fig. 9. The thermal acclimation of twitch force by indirect stimulation. Frogs were kept for 0, 1, 2 or 3 months at 4°C and twitch forces were measured at resting muscle length (l₀) at 4°C. Twitch forces are expressed as values relative to those obtained by direct stimulation at l₀ at 4°C. The numbers at data points indicate the number of preparations used. ^*Differences between two data points marked by horizontal lines are statistically significant by P<0.01.