In this regard, we hypothesized that the mode of cold adaptation for haenyeos would switch over to local body adaptation from the overall body adaptation in line with the change to thick wetsuits from thin cotton bathing suits. For this reason, fishermen, divers, and swimmers who frequently immerse a part or all of their body in water can experience considerable body heat loss, even when the water temperature is only mildly cool. 0.025 W/mK), and heat conductance from unprotected skin can be more than dozens of times greater in water than in air at the same temperature. Water has a much higher thermal conductivity than air (0.58 vs. In other words, wetsuits protected older haenyeos from severe cold stress in winter but induced local exposure to mild cold over the face and hands because of prolonged diving hours. Now, their body is insulated by thick wetsuits but the face and hands are still exposed to cold stress. Haenyeos’ whole body used to be exposed to severe cold stress in their youth because they wore only thin cotton swimsuits at that time. The older haenyeos have been diving more than 50 years since their teens. Moreover, 57% of the 4005 haenyeos are in their seventies or older. At present, 88% of haenyeos are over their sixties. The number of Jeju haenyeos, who are currently working under the sea, rapidly decreased to 4005 in 2015 from 14,143 in 1970. Since then, investigations on haenyeos’ thermoregulatory responses to cold have waned. One of the classic studies by Hong’s group found that the cold-adaptive properties of haenyeos disappeared as they began to wear new wetsuits instead of traditional cotton bathing suits in the mid-1970s. Because of their particular diving practices with thin cotton or thick wet diving suits, professor Suk-Ki Hong and his colleagues investigated young haenyeos’ cold acclimatization and deacclimatization in terms of environmental physiology in the 1960s to the 1980s. Sea water temperature in winter is on average 13–14 ☌ at Jeju island and haenyeos had dived even in the middle of winter wearing only thin cotton bathing suits until the late 1970s. Until the early 1980s, haenyeos were known as being more tolerable to cold water than other divers due to their diving practices in winter. During the nineteenth century, 22% of the entire female population in Jeju were haenyeos. The word haenyeo literally means “sea women” in Korean and corresponding to ama in Japanese. In 2016, the culture of Jeju haenyeo, Korean breath-hold women divers, was inscribed on the representative list of the intangible cultural heritage of humanity of the United Nations Educational, Scientific and Cultural Organization (UNESCO). Further studies on cross-adaptation between chronic cold stress and heat tolerance are needed. It was known that cold-adaptive traits of haenyeos disappeared, but we confirmed that cold-adaptive traits are still retained on the face and hands which could be interpreted by a mode switch to local adaptation from the overall adaptation to cold. An interesting finding was the possibility of positive cross-adaptation which might be supported by greater heat tolerance and cutaneous warm perception thresholds of older haenyeos who adapted to cold water. However, thermal perception in cold reflected aging effects rather than local cold acclimatization. Finger cold tests supported more superior local cold tolerance for older haenyeos than for older non-diving females. Our findings were that older haenyeos still retain local cold tolerance on the extremities despite their aging. As control group counterparts, older non-diving females and young non-diving females were compared with older haenyeos in the controlled experiments. Methodsįor the past several years, we revisited and explored older haenyeos in terms of environmental physiology, beginning with questionnaire and field studies and later advancing to thermal tolerance tests in conjunction with cutaneous thermal threshold tests in a climate chamber. For social and economic reasons, the number of haenyeos rapidly decreased to 4005 in 2015 from 14,143 in 1970 and the average age of haenyeos is about 75 years old at present. However, their overall cold-adaptive traits have disappeared since they began to wear wetsuits and research has waned since the 1980s. During the 1960s to the 1980s, haenyeos received attention from environmental physiologists due to their unique ability to endure cold water while wearing only a thin cotton bathing suit. We have been studying the thermoregulatory responses of Korean breath-hold women divers, called haenyeo, in terms of aging and cold adaptation.
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