title: Water temperature and intensity of exercise in maintenance of thermal equilibrium.
abstract: This study examined the thermal and metabolic responses of six men during exercise in water at critical temperature (Tcw, 31.2 +/- 0.5 degrees C), below Tcw (BTcw, 28.8 +/- 0.6 degrees C), at thermoneutrality (Ttn, 34 degrees C), and above Ttn (ATtn, 36 degrees C). At each water temperature (Tw) male volunteers wearing only swimming trunks completed four 1-h experiments while immersed up to the neck. During one experiment, subjects remained at rest (R), and the other three performed leg exercise (LE) at three different intensities (LE-1, 2 MET; LE-2, 3 MET; LE-3, 4 MET). In water warmer than Tcw, there was no difference in metabolic rate (M) during R. The M for each work load was independent of Tw. Esophageal temperature (Tes) remained unchanged during R in water of ATtn (36 degrees C). However, Tes significantly (P less than 0.05) declined over 1 h during R at Ttn (delta Tes = -0.39 degrees C), Tcw (delta Tes = -0.54 degrees C), and BTcw (delta Tes = -0.61 degrees C). All levels of underwater exercise elevated Tes and M compared with R at all Tw. In water colder than Tcw, the ratio of heat loss from limbs compared with the trunk became greater as LE intensity increased, indicating a preferential increase in heat loss from the limbs in cool water. Tissue insulation (Itissue) was lower during LE than at R and was inversely proportional to the increase in LE intensity. A linearly inverse relationship was established between Tw and M in maintaining thermal equilibrium.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Sagawa
authors.forename: K
authors.initials: K
authors.lastname: Shiraki
authors.forename: M K
authors.initials: MK
authors.lastname: Yousef
authors.forename: N
authors.initials: N
authors.lastname: Konda
mesh_terms: D000328:Adult; D001831:Body Temperature; D001833:Body Temperature Regulation; D006801:Humans; D007101:Immersion / Q000009:adverse effects / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D005082:Physical Exertion; D012768:Shivering; D013696:Temperature; D013816:Thermodynamics