Thermal insulation and shivering threshold in Greek sponge divers

Sublingual temperature (T(or)), average skin temperature [T̄(sk)], and skin heat flow (H(sk)) were determined in a field study for six Greek sponge divers and seven nondiving controls during head-out immersions at water temperature of 21°C. Wetsuits kept T̄(sk) at 22-28°C for 1-3 h until T(or) fell to 36.5-35.5°C and violent shivering [metabolic rate (M) = 100-150 W.m-2] ended the test. At a steady T̄(sk), immediately before shivering, overall tissue insulation (It), calculated as (T(or) - T̄(sk)/H(sk), 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 T(or) for a T̄(sk) of about 26° C, and the relationship of M vs. T(or) (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.