A methodical approach is described, attempting to separate the loss of heat and moisture due to forced exchange of air inside clothing, when walking, from the loss caused by gradients between the body and the environment. Temperature, heat flow, and relative humidity were recorded on the skin of the back and inside the respective clothing (shirt only, vest and shirt, or vest, shirt and anorak) in 12 experiments performed in a climatic chamber at 4-11°C and 35-70% RH, The subject walked on a treadmill with 5% grade at 7.2 km/hr until a new steady state of higher tempera ture and heat flow, as well as humidity, resulting from evaporation of sweat, was reached. When the motion was suddenly stopped, both the temperature and humidity increased steeply, while the heat flow decreased, showing levels which would have been attained, theoretically, if the transfer of heat and water vapor along gradients was not assisted by forced exchange of air when walking. When walking was resumed after a pause, all recorded parameters changed in the opposite direction. Continuous recording of temperature next to skin showed temperature oscillations synchronous either with every step or with every other step. The results are considered as evidence of the effect of forced ventilation on the microclimate. Calculated from changes in water-vapor pressure, the magnitude of forced ventilation corresponded, approximately, to dilution of the air layer next to skin, with atmospheric air, by one-half of its volume. It was demonstrated, in addition, that the heat of sorption, arising from transient increases of humidity in the clothing, had a marked effect on temperature of the micro-climate. The term "bellows ventilation" is thought to express best the mechanism of exchange of air resulting from rhythmical movements of limbs and body at physical activity.
Relations were studied between skin temperature of the back as well as temperature and humidity inside clothing, and subjective estimates of thermal, humidity, and comfort sensations in 5 subjects wearing cross-country ski dress. The 2-h wear trials were performed in a climatic chamber at −2°C and simulated the actual circumstances under which such a dress is worn by alternating periods of intensive walking (20 min) on a treadmill with periods of resting (5–10 min). Each subject participated in 4 trials wearing alternately one of the 4 experimental, double-layer vests (double-cotton, cotton-polypropylene with cotton layer next to skin, same combination with polypropylene layer next to skin, double-polypropylene). Skin temperature of the back was during the experiments systematically lower ( P<0.05) by about 1°C with the double-layer cotton vest than with the double-layer polypropylene vest. Since the physical parameters of the two fabrics were not identical, the findings cannot be definitely attributed to the inherently different properties of the fibers. No significant differences were found in the 4 experimental series either in other objective measurements (temperature and humidity of the microclimate, energy output, total amount of sweat, amount of sweat trapped in the vests) or in subjective estimates of thermal, humidity, and comfort sensations. Gradual increase of skin temperature as well as of temperature and humidity (sweating) of the microclimate was recorded during walking periods. When walking was interrupted by a pause, both the temperature and humidity rose steeply, due to the cessation of bellows ventilation of the clothing, and fell again when walking was resumed. The thermal and humidity sensations on the back reported after the turning-points of the intermittent activity showed opposite direction of changes than those of the recorded parameters— i.e., decrease during pauses and increase after walking was resumed. It is possible that the perception of local sensations was affected by superimposed, central perception of changes in the amount of heat delivered from muscles to the brain receptors. The sensations of comfort seemed to be affected mostly by perception of “warmth” when walking and “cold” when resting.
Wear trials of a woven and a knitted Scandinavian cross-country ski dress with identical underwear and other garments were performed in a climatic chamber on 5 subjects who walked at -9°C on a treadmill with a 5% grade for a total of 2 hr, changing the velocity of the walk every 20 mins from 4.1 to 6.7 km/hr. The energy output corresponded to 200, and 350 kcal/m 2 hr, respectively.One-half of the produced sweat did not evaporate during the experiments and remained trapped in the clolhing. Though the dress proper and its underwear covered two-thirds of the body surface area (trunk, arms, thighs), more than one-half of the not evaporated sweat was found in the garments of the peripheral area (head, hands, legs, feet). The vest contained a high amount of water, and the same partial pressure of water vapor was recorded in the spaces on either side of it, indicating that the beginning of the effective diffusion gradient through the clothing was shifted from the skin to the outer side of the vest. In the absence of wind in the trials, the clinging knitted dress assembly had a higher thermal resistance than the loosely cut woven one. But, subjectively, the woven assembly was felt to be warmer than the knitted which contained more trapped sweat. The rectal and skin temperature, the temperature and humidity in the spaces between the clothing, and the subjective thermal and humidity sensations reflected well, by regular oscillations, the cyclic changes in the intensity of metabolism. The general thermal sensations correlated better with the weighted average of the rectal and mean skin temperature than with either temperature alone. However, in the quick walking periods, the general thermal sensations were the same as the sensations in the peripheral body area, while the rating of the sensations in the central area under the dress proper was distinctly lower. Special attention should be paid to the role of the peripheral parts of the body in the evaluation of clothing comfort.
The Scandinavian cross-country ski dress covers only about two thirds of the body surface area (trunk, arms and thighs). The peripheral area (head, hands, legs, and feet) is covered by garments which are not an integral part of the dress. Selective cooling of the peripheral area in six subjects in a climatic chamber showed that a general feeling of being cold was achieved by lowering the skin temperature in the peripheral area. The same general thermal sensation was also arrived at by keeping the peripheral area warm and cooling the central skin area. 'I'he general thermal sensation was related to the average weighed skin temperature, irrespective of the location of the cold and warm surface areas. In the evaluation of thermal comfort of any clothing system, attention should be paid to the insulation of the parts of the body which are not covered by the garments under investigation.
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