Fig. 4. Fatigue index. The fatigue index is a measure of the percent of force production capacity remaining after a fatiguing series of contractions, and is thus a measure of muscle endurance. The fatigue index of semitendinosus muscles from the four groups was significantly increased only by cold acclimation, and the CT group showed the highest resistance to fatigue. 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.