Cutaneous warmth and hotness thresholds to radiation heat exposure at a distance of 10 cm from 17 body regions

The purpose of the present study was to evaluate body regional differences in cutaneous warmth and hotness thresholds in relation to radiant heat exposure. Fourteen male subjects participated in this study (age: 25 & PLUSMN; 5 y, height: 176.6 & PLUSMN; 5.5 cm, body weight: 70 & PLUSMN; 5.8 kg). Cutaneous warmth and hotness thresholds were measured on the forehead, neck, chest, abdomen, upper back, lower back, upper arm, forearm, palm, back of hand, front thigh, shin, top of foot, buttock, back thigh, calf, and sole. The forehead (34.8 & PLUSMN; 0.2 degrees C), lower back (34.1 & PLUSMN; 1.2 degrees C) and palm (34.3 & PLUSMN; 0.7 degrees C) had the highest warmth thresholds, whereas the foot (29.8 & PLUSMN; 1.9 degrees C) and sole (28.0 & PLUSMN; 2.1 degrees C) had the lowest values among the 17 regions (P<0.001). Higher warmth thresholds were related to higher initial skin temperatures (Tsk) (r=0.972, P<0.001). Increases in Tsk for detecting warmth sensation were smaller for the lower back with a rise of 0.2 & PLUSMN; 0.4 degrees C and the abdomen (0.3 & PLUSMN; 0.3 degrees C) than for the buttock (0.9 & PLUSMN; 0.8 degrees C) and sole (0.8 & PLUSMN; 0.6 degrees C) (P<0.05). Increases in Tsk for detecting hotness sensation ranged from 0.5 to 1.5 C. Warmth and hotness thresholds on the abdomen or sole had significant relationships with body mass index, indicating that the overweight are less sensitive to detecting radiant heat on the abdomen or sole. Thermal thresholds from radiant heat exposure of 100 cm2 were lower than the values from conductive heat exposure of 6.25 cm2, which might be explained by the effect of spatial summation.

Automated summary

The purpose of this study was to evaluate regional differences in cutaneous warmth and hotness thresholds in response to radiant heat exposure. Measurements were taken on 17 body regions, and it was found that the forehead, lower back, and palm had the highest warmth thresholds, while the foot and sole had the lowest values. It was also observed that thermal thresholds from radiant heat exposure were lower than those from conductive heat exposure.