Biological significance of maturation-and aging-related changes in environmental adaptability

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This research project addressed the ways in which environmental adaptability change with maturation and aging from the viewpoint of whole body coordination. Our cross-sectional and longitudinal (for 10 yrs) findings suggest that age-related decrement in heat loss effector function may involve cutaneous vasodilation, sweat output per gland, and active sweat gland density in that order. The successive decrement may proceed from the lower limbs to the back of the upper body, the front of the upper body, then the upper limbs and finally to the head. From results of heat-and acetylcholine-induced (including axon reflex) sweating tests, and skin thermal sensitivity test in the same older and younger men, we also discovered that the age-related decrement of thermoregulatory mechanisms may involve the skin thermal sensitivity, the cholinergic sensitivity of sweat glands, and the activities of the central sudomotor and sympathetic nerves in that order. Furthermore, our results of femoral artery … More blood flow and other measurements during passive heating and knee extension exercise suggest that the age-related decrement in the peripheral circulation (skin blood flow) may precede that in the central circulation (artery blood flow). Our data during isometric handgrip (IH) exercise in hot condition suggest that non-thermal heat loss responses decline with aging and the declines may be similar to those of thermal heat loss responses in the order of aging process.The data of sweating and rectal temperature during sports activity in summer suggested that prepubertal boys have an underdeveloped sweating function. The data during the heat stress (air temperature (T_a) was linearly increased from 28℃ to 40℃ over 60 min) suggested that compared with young men, prepubertal boys manifest greater physiological and perceptual strain under heat stress induced by T_a exceeding mean skin temperature, which is most probably attributable to a combination of lower evaporative heat loss, as evidenced by lower SR, and greater heat gain owing to a larger surface area-to-mass ratio. Our data during IH exercise suggest that prepubertal boys have underdeveloped non-thermal heat loss responses (remarkably in sweating rather than cutaneous vasodilation) and the underdeveloped responses may be similar to those of thermal heat loss responses in the order of maturation process. Less