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4.3.3. Fuentes garantizadas de prestamos a corto plazo
The size and fit of a garment has direct influence on the comfort characteristics. In a loose-fitting garment the volume of entrapped still air is more and has larger openings at places like the neck, waist, wrist, and ankles, which cause greater reductions in their thermal insulation and moisture vapour resistance during windy conditions and body movement.
Figures 8.1a and 8.1b show the typical shapes of loose-fit and tight-fit garments [3]. The tight-fit garment is designed to fit tight to the skin in order to allow the technical aspects of the garment to work effectively.
However, no such garment should be so tight as to restrict freedom of movement. Generally the tight-fit garment is designed to fit all contours of the body and compress core muscle groups. The normal-fit garment, on the other hand, provides a less tight-fit but still provides all the benefits of moisture transmission and thermal management in appropriate locations.
The loose-fit garments are designed as a comfort fit with all the moisture management benefits and generally worn as a casual garment or an outer garment. In a research work conducted by McCullough et al. [4], the thermal insulation of two pairs of loose-fitting and two pairs of corresponding tight-fitting long trousers were measured, using a standing manikin in little wind (air velocity in the chamber was less than 0.11 m/s).
They have observed that the loose-fitting trousers have much greater thermal insulation than the corresponding tight-fitting trousers (33% more for the tweed trousers and 48% more for the denim trousers). In another
study conducted by Havenith et al. [5] the thermal insulation of three clothing ensembles on four combinations of body postures and movements (two with loose fit and two with tight fit) when the subjects were sitting and walking at two speeds and at three wind speeds were determined.
They have concluded that the tight-fit clothing had 6–31% less insulation than loose-fit clothing. The difference in thermal insulation values between tight-fit and loose-fit clothing was found to be maximum in sitting condition. They have also observed that the difference in thermal insulation value was lower in presence of wind.
8.1a Typical loose-fit garment. 8.1b Typical tight-fit garment. [3]
8.3.2 Garment fit and pressure
The comfort related to garment pressure and fit mainly depend on the tactile responses of human body which include thermal and moisture perceptions, prickle related to allergic reactions and reactions to the surface texture of materials, friction between clothing and skin surface and pressure sensations. Two categories of tactile sensations are somesthetic sensations and kinesthetic sensations. The somesthetic sensations are touch response from the nerves in the surface of the skin. Tickle, prickle and abrasion are somesthetic responses to clothing. The kinesthetic sensations or the deep pressure sensations are felt by the nerves in the muscles and the joints [6].
Pressure sensations created by the resistance of the garment to movement and the weight of the garment in response to movement are kinesthetic responses to clothing fit [7].
The multidirectional and random forces generated during dynamic interactions between a garment and a moving human body generates pressure sensations. The discomfort level of clothing pressure was found to be between 60 and 100 g/cm2, depending on the individual and the part of the body concerned, which is similar to blood pressure in the capillary
blood vessels near the skin surface [8]. So, the pressure exerted by a garment is an important design criterion and is affected by its style, fit and mechanical properties. It is directly related to the degree of space allowance (F, the difference between the surface areas of garment and body) between the body and the garment during body movement. According to the degree of space allowance (F), garments can be classified into three types:
foundation garments (F < 0), perfectly fitting garments (F = 0) and loose fitting garments (F > 0). In foundation garment the area of garment is less than the body area (such as women’s close-fitting foundation garment, pressure garment, etc.). These are mainly designed to apply a certain level of pressure on the body part concerned when the body is in active condition or at rest. The perfectly fitting garments are those where the garment area is exactly equal to the body area (such as tights, socks, body stockings, etc.) and have a figure-shaping function but are not designed to apply pressure to the body. Therefore, a perfectly fitting garment only restricts body movement as a result of garment pressure, but no pressure is applied when the body rests. In loose-fitting garments the area of the garment is larger than the body area (such as loose-fit outer wear, casuals etc.). As the movement of body can reduce the space allowance, loose-fitting garments may also sometime exert pressure on the body at contact areas.
Therefore, the level of garment pressure varies significantly for different wear situations, depending on four factors namely, design and fit of the garment, shape of the body part, mechanical properties of the underlying tissue, and mechanical properties of the fabrics [9].
The evaluation of human comfort due to garment fit and subjective garment pressure sensations are generally done by conducting wear trials [10–12]. In the study conducted by Makabe et al. [11] the garment pressure was measured on the covered area at the waist for corsets and waistbands and conducted a sensory test for garment pressure. Their results indicate that the garment pressure at the waist is influenced by the area covered, respiration and the ability of the garment to assume the complex body curvature during the body movement. During subjective evaluation of garment pressure and comfort sensations at the waist, they have observed that in the lower garment pressure range (0–15 gf/cm2) no sense of discomfort is there. In the medium range of garment pressure (15–25 gf/cm2) negligible or only slight discomfort is perceived. But in higher pressure range, i.e. when the garment pressure exceeds 25 gf/cm2, extreme discomfort is perceived. Denton [8] pointed out that as the body curvature increases the garment pressure on the body increases. The body curvature of average women’s waist at the sides is roughly 3.5 times greater than that at the front, so unwanted pressure on the sides of the waist is 3.5 times greater than the desired figure flattening pressure on the front [9].
Similar finding has also been reported during the measurement of internal pressure exerted by pressure bandage using Laplace equation [13]. As per the Laplace equation it is expected that the exerted internal pressure (P) would increase with increase in curvature of the limb. The Laplace equation is given below,
P = T×nr×w (8.1)
where T is tension of bandage during wrapping; n is number of wraps; r is radius of curvature; and w is width of bandage.
8.3.3 Evaluation of tactile perception to fit
Various methods have been developed to measure the human perceptions, like odours, tastes etc. Ashdown and DeLong [7] adapted the test method for measuring tactile perception to fit, which was developed by the ASTM Committee E-18 for sensory evaluation of products. Constant stimulus difference (i.e. difference from control value) test was used as the model in the development of the perception of fit tests. Two types of thresholds were identified by this test: the difference threshold (or) the extent of change in the stimulus that produces a noticeable difference; and the recognition threshold (or) the extent of change in a stimulus necessary for positive identification of the difference. In the first part of this test a series of garments (pants) along with their corresponding control (garments) were presented to a panel of experts. The experts then rated the difference of the sample from the control. The scale for pants provided the response choices of ‘looser’, ‘a little looser’, ‘the same’, ‘a little tighter’ and ‘tighter’
for the waist, hips and crotch. The second part of the perception test was designed to address the large number of interactions that occurred in the first part of the perception test. In order to focus the subjects’ attention on one area of concern, they were told what area of the test samples (pants) would vary from the control sample. The second test was therefore performed with variations at a single location. Two experts were asked to respond to test samples (pants) with hip or crotch variations. In the second type of perception test, the experts were informed that the variations were all at this specific location. The final perception test was carried out to determine the significance of the thresholds perceived in relation to comfort or discomfort perceptions with garment fit. The participants were given only the test garment that they had perceived as different from the control to try on in a preference test. A mirror was provided and subjects were asked to indicate whether they found the garments are comfortable or not, even though they perceived differences from the control garment.
Psychophysical scaling technique was used by You et al. [14] to assess the pressure perception and other relative wearing sensations during wearer trials of tight-fitting garments. The sense of pressure was recorded on a scale of 0–10. One tight-fitting pant, with very high clothing pressure, as presented to subjects as the standard for the maximum degree of pressure, was indexed as 10. On the other hand, when the subject was naked, i.e. at the minimum degree of pressure, the scale was indexed as 0. The subjects were asked to rate the sense on a scale 0–10. Every subject was asked to assess the pressure sensation of each area while wearing the garments.