Local differences in sweat secretion from the head during rest and exercise in the heat

Abstract

The importance of the head in dissipating body heat under hot conditions is well recognised, although very little is known about local differences in sweat secretion across the surface of the head. In this study, we focused on the intra-segmental distribution of head sweating. Ten healthy males were exposed to passive heating and exercise-induced hyperthermia (36 degrees C, 60% relative humidity, water-perfusion suit: 46 degrees C), with ventilated sweat capsules (3.16 cm(2)) used to measure sweat rates from the forehead and nine sites inside the hairline. Sweat secretion from both non-hairy (glabrous) and hairy areas of the head increased linearly with increments in work rate and core temperature, with heart rate and core temperature peaking at 175 b min(-1) (+/-6) b min(-1) and 39.2 degrees C (+/-0.1). The mean sweat rate during exercise for sites within the hairline was 1.95 mg cm(-2) min(-1). However, the evolution of this secretion pattern was not uniformly distributed within the head, with the average sweat rate for the top of the head being significantly lower than at the anterior lateral aspect of the head (P < 0.05), and representing only 30% of the forehead sweat rate (P < 0.05). It is hypothesised that these intra-segmental observations may reflect variations in the local adaptation of eccrine glands to differences in local evaporation associated either with bipedal locomotion, which will influence forehead sweating, or the hidromeiotic suppression of sweating, which impacts upon sweat glands within the hairline.

Sweat secretion from the torso during passively-induced and exercise-related hyperthermia

“…In general, sweat gland densities are higher at the forehead, hand and foot, and lower on the thigh and leg, with the arms and trunk displaying intermediate densities (Thompson 1954;Szabo 1962Szabo , 1967Knip 1969;Hwang and Baik 1997). A caudalto-rostral pattern of sweat onset has been demonstrated for resting subjects (Randall and Hertzman 1953), with higher thermal sweat secretions usually observed at the forehead during resting and exercising states (Cotter et al 1995;Machado-Moreira et al 2007b). These generalisations are well accepted, but there is a paucity of knowledge concerning diVerences in sweat secretion within body segments.…”

A comparison of galvanic skin conductance and skin wettedness as indicators of thermal discomfort during moderate and high metabolic rates

“…Reliability was assessed during pilot tests and whilst some variations did exist the response to a given condition was similar. The large variation in individual sweat gland output may accounts for the variation seen in GSC but also in that from other studies when measuring sweat (Smith & Havenith, 2011, 2012Cotter et al 1995;Machado-Moreira et al 2008). Standardising the value relative to a baseline value aimed to reduce these errors but the high dispersion of values reduces the certainty of predicting thermal discomfort using GSC as can be seen in Table 3 and 4.…”

Improved Procedure for Estimating Time-dependent Changes in Local Sweat Rates by Measuring Local Sweat Volumes

“…The ventilated capsule (7.1 cm 2 ) was fixed to the upper section of the left scapula and the local sweat rate (LSR vc ) was measured during the exercise by using the ventilated capsule method [3][4][5][6][7][10][11][12][13]15,16] After the exercises, a part of the absorbent pad was pulled out from each of the tailored pads fixed on the skin. Each absorbent pad was quickly placed, separately, into an impermeable plastic Ziploc bag and weighed with the bag.…”

“…Previous studies of regional sweat rates found that the local sweat rate (LSR) clearly varies among the different body sites [1][2][3][4][5][6], and that LSR on the forehead and torso was greater than that of the limbs [1][2][3][4]. Some studies have focused on the differences in sweat regulation depending on maturation and aging [7][8][9][10][11], sex [12,13], fitness [8,14,15], and heat acclimation [8,16] to elucidate the mechanism underlying thermoregulation.…”

“…Some studies have focused on the differences in sweat regulation depending on maturation and aging [7][8][9][10][11], sex [12,13], fitness [8,14,15], and heat acclimation [8,16] to elucidate the mechanism underlying thermoregulation. LSR is measured by using a ventilated capsule, and is estimated from the difference in vapor content between the influx and efflux air moving through the capsule at a known flow rate [3][4][5][6][7][10][11][12][13]15,16]. A few small capsules with less than 10 cm 2 in the project areas were generally used, with one capsule per one body part in the majority of previous studies.…”