Fig. 2. Kinetics of single twitch contractions. (A) Time to peak tension per gram of force produced (TPT_g) for single twitches of the semitendinosus muscle by the four experimental groups (as in Table 1) was significantly increased by cold acclimation but not by exercise training. There is a trend for increased time required to generate force with either the TnT or CS treatment group, but only those animals subjected to both treatments (CT) showed a statistically significant slowing of twitch speed. (B) Half relaxation time per gram of force produced (RT_g) for single twitches by semitendinosus muscles of the four experimental groups. The RT_g was significantly longer in cold-acclimated but not by exercise-trained animals. Both cold groups had a longer relaxation rate; however, post-hoc pairwise comparison showed this effect was only statistically significant in the CT group. Values are means ± S.E.M. and different superscripted letters indicate significant pairwise differences between groups. CS, cold, sedentary; CT, cold, trained; TnS, thermoneutral, sedentary; TnT, thermoneutral, trained.