Contribution of central versus sweat gland mechanisms to the seasonal change of sweating function in young sedentary males and females

Abstract

In summer and winter, young, sedentary male (N = 5) and female (N = 7) subjects were exposed to heat in a climate chamber in which ambient temperature (Ta) was raised continuously from 30 to 42°C at a rate of 0.1°C min(-1) at a relative humidity of 40%. Sweat rates (SR) were measured continuously on forearm, chest and forehead together with tympanic temperature (Tty), mean skin temperature (⁻Ts) and mean body temperature ⁻Tb. The rate of sweat expulsions (Fsw) was obtained as an indicator of central sudomotor activity. Tty and ⁻Tb were significantly lower during summer compared with winter in males; SR was not significantly different between summer and winter in males, but was significantly higher during summer in females; SR during winter was higher in males compared with females. The regression line relating Fsw to ⁻Tb shifted significantly from winter to summer in males and females, but the magnitude of the shift was not significantly different between the two subject groups. The regression line relating SR to Fsw was steepened significantly from winter to summer in males and females, and the change in the slope was significantly greater in females than in males. Females showed a lower slope in winter and a similar slope in summer compared to males. It was concluded that sweating function was improved during summer mediated by central sudomotor and sweat gland mechanisms in males and females, and, although the change of sweat gland function from winter to summer was greater in females as compared with males, the level of increased sweat gland function during summer was similar between the two subject groups.

Improved neural control of body temperature following heat acclimation in humans

“…These studies reported a greater sweat gland expulsion frequency, a proposed marker of central sudomotor activity, following heat acclimation (Ogawa & Sugenoya, 1993) and seasonal acclimatization (Taniguchi et al . 2011). By contrast, we determined how heat acclimation modulates skin sympathetic nerve activity, comprising the efferent neural signal that activates sweating and cutaneous vasodilatation (Hagbarth et al .…”

The effect of perspiration on the sEMG amplitude and power spectrum

“…These effects could result in interpretation errors of sEMG findings in human performance studies, depending on the nature of the study and onset of signal deterioration. Furthermore, the rate of sweating changes over time, being dependent on: passive heating (Taniguchi et al, 2011), exercise (Flouris and Cheung, 2010;Smith and Havenith, 2011) and influenced by individual differences in sweat rates (Cotter et al, 1995) as well as time of day (Aoki et al, 2002), seasons (Aoki et al, 2002), gender (Kenny and Jay, 2007;Taniguchi et al, 2011) and age (Dufour and Candas, 2007). This makes sweating a difficult factor to control in experimental studies, especially those carried out in the workplace where the environmental conditions cannot be controlled and protective clothing is often required.…”

“…Little is known regarding the amount of sweat needed to accumulate before signal fidelity deteriorates. Thresholds for sweating have been reported as low as 36°C body temperature with passive heating (Taniguchi et al, 2011) and 10 min of graded exercise reaching 20% VO 2max (Takano et al, 1996) indicating that sweating is a factor in most workplace studies that are investigating physical work demands. Maximal sweat rates have been shown to occur along the length of the spine and across the mid back (Havenith et al, 2008;Smith and Havenith, 2011) at rates exceeding 2000 mg m À2 h À1 with high intensity exercise.…”

Age‐ and sex‐related differences in sudomotor function evaluated by the quantitative sudomotor axon reflex test (QSART) in healthy humans

“…Of these, age and sex are major elements determining how humans modulate homeostasis between the environment and body temperature. Differences in sweat gland function are observed between male and female subjects . Older women show a lower whole‐body sweating rate than young women because aging attenuates the sweat gland response and mechanism controlled by a central sudomotor mechanism .…”

“…Efferent sweat fibres originate in the preoptic area and anterior hypothalamus and descend to the post‐ganglionic sympathetic plexus (sudomotor neurons) through the ipsilateral brain stem and medulla . The sweat glands generate a sweat response to central sudomotor nerve activity . In addition, peripheral conditions (local skin temperature and blood flow) can modulate the sweating response …”