Thermal insulation and shivering threshold in Greek sponge divers.

Sublingual temperature (Tor), average skin temperature (Tsk), and skin heat flow (Hsk) were determined in a field study for six Greek sponge divers and seven nondiving controls during head-out immersions at water temperature of 21 degrees C. Wetsuits kept Tsk at 22-28 degrees C for 1-3 h until Tor fell to 36.5-35.5 degrees C and violent shivering [metabolic rate (M) = 100-150 W . m-2] ended the test. At a steady Tsk, immediately before shivering, overall tissue insulation (It), calculated as (Tor--Tsk)/Hsk, was linearly related to mean subcutaneous fat thickness (MFT) in both groups without statistical difference between them. The onset of shivering, as detected by a sharp increase of M, occurred at the same Tor for a Tsk of about 26 degrees C, and the relationship of M vs. Tor (i.e., metabolic sensitivity) was the same for both groups. Contrary to other groups accustomed to diving in cold water, the use of a wetsuit for a long time has evidently prevented cold adaptation in these divers.