Tomihiro Shimizu

Human thermoregulatory responses during prolonged walking in water at 25, 30 and 35°C

Abstract Eight healthy and physically well-trained male students exercised on a treadmill for 60 min while being immersed in water to the middle of the chest in a laboratory flowmill. The water velocity was adjusted so that the intensity of exercise correspond to 50% maximal oxygen uptake of each subject, and experiments were performed once at each of three water temperatures: 25, 30, 35°C, following a 30-min control period in air at 25°C, and on a treadmill in air at an ambient temperature of 25°C. Thermal states during rest and exercise were determined by measuring rectal and skin temperatures at various points, and mean skin temperatures were calculated. The intensity of exercise was monitored by measuring oxygen consumption, and heart rate was monitored as an indicator for cardiovascular function. At each water temperature, identical oxygen consumption levels were attained during exercise, indicating that no extra heat was produced by shivering at the lowest water temperature. The slight rise in rectal temperature during exercise was not influenced by the water temperature. The temperatures of skin exposed to air rose slightly during exercise at 25°C and 30°C water temperature and markedly at 35°C. The loss of body mass increased with water temperature indicating that both skin blood flow and sweating during exercise increased with the rise in water temperature. The rise in body temperature provided the thermoregulatory drive for the loss of the heat generated during exercise. Heart rate increased most during exercise in water at 35°C, most likely due to enhanced requirements for skin blood flow. Although such requirements were certainly smallest at 25°C water temperature, heart rate at this temperature was slightly higher than at 30°C suggesting reflex activation of sympathetic control by cold signals from the skin. There was a significantly greater increase in mean skin and rectal temperatures in subjects exercising on the treadmill in air, compared to those exercising in water at 25°C.

Effects of Hot Deep Seawater Bathing on the Immune Cell Distribution in Peripheral Blood from Healthy Young Men

ObjectivesDeep seawater (DSW) utilization technology has been developed for the fields of medicine and health, among others. To clarify the health effects of DSW as compared with surface seawater (SSW) or tap water (TW), we investigated the changes of immune cell distribution of the peripheral blood, or subjective judgment scores, after hot water bathing.MethodsTen healthy young men were immersed for 10 min in DSW, SSW and TW heated to 42°C. Blood samples were collected before bathing, immediately after bathing and 60 min after bathing. Total and differential numbers of leucocytes and lymphocyte subsets (CD3, CD4, CD8, CD19, CD16, and CD56) were examined using an automated hematology analyzer and a flow cytometer, respectively. The subjective judgment scores were obtained by an oral comprehension test.ResultsSince the pre-bathing leukocyte count in the TW group was significantly different from those in the DSW and SSW groups, we excluded the findings of TW bathing from consideration. In hot DSW bathing, CD8-lymphocytes increased significantly immediately after bathing (p<0.05), in contrast to hot SSW bathing, in which no significant changes were detected in the lymphocyte subsets. Additionally, there were no significant changes between repeated measurements in the subjective judgment scores, though the score of thermal sensation in SSW bathing showed a significantly higher value immediately after bathing than before bathing (p<0.01).ConclusionsOur findings suggest that increased CD8-lymphocytes in hot DSW bathing may improve human immune function as well as hot springs do, as compared with SSW bathing. Although hot DSW bathing may have the ability to change human immune cell distribution, well-designed studies are needed to clarify the health effects including not only DSW and SSW but also TW.