Fig. 4. Normalised increases in tailshaker muscle peak tension (open circles) and tension–time integral (TTI, filled circles) per twitch during rattling in western diamondback rattlesnakes (Crotalus atrox). Between 10 and 30°C (26–77 Hz), muscle twitch tension increased an average of 3.5-fold whereas TTI increased by only 1.3-fold. The trend for tension increase is y=0.084x–1.100 (r²=0.79, P<0.001), and that for TTI increase is y=0.016x+0.660 (r²=0.47, P<0.001); N=9 snakes. The slopes are significantly different, as indicated in the text.