Nonshivering thermoregulatory responses in trained athletes: effects of physical fitness and body fat.

We studied the difference of thermoregulatory responses between trained male athletes (TR, n = 9) and untrained men (UT, n = 7) during 60 min of cold exposure (15 degrees C) without shivering, and examined the effects of physical fitness and body fat on these responses. Mean skin temperature (Tsk), esophageal temperature (Tes), and skin conductance (Kb) were similar between TR and UT, and heat production (M) for TR increased significantly during exposure at 15 degrees C. The M at 15 degrees C correlated positively with maximal oxygen uptake and negatively with body fat (%BF), but not with Tes. The Kb correlated negatively with Tes and positively with Tsk. The %BF also correlated negatively with Kb and Tsk during exposure at 15 degrees C, and the slope of %BF vs. Tsk relationship was significantly steeper in TR than in UT. These results suggest that (1) body temperature is maintained by the reduction of skin conductance, and (2) heat insulation independent of body fat is enhanced in trained athletes during cold exposure without shivering.