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example, in specialised sports such as cycling, aerodynamics is a critical ..... distance calculated from the difference between the person's dimensions .... separate test sessions to determine physical performance) using eight male .... assigning that size, one size larger and one smaller, for the trial. ...... From Holmer (1985).
CLOTHING, TEXTILES, AND HUMAN PERFORMANCE R.M. Laing and G.G. Sleivert

1. INTRODUCTION 1.1 Background Much has been written about the particular properties of textiles and some other materials which affect the manufacture and performance of clothing, but much less is known about the effects of clothing on human performance. Extrapolation from the known performance of fabric properties to the likely performance of garments manufactured from those fabrics has been fairly common despite some evidence of only limted veracity. Fibre producers often use selected properties of fibres as the basis for claiming properties of garments made from materials which were made from those fibres. These practices are evident among producers of generic fibre types (e.g. merino wool, or cotton) as well as among producers of branded fibres (e.g. Du Pont and Lycra). Claims made about fabric properties may also be extrapolated to garment properties and thence explicitly or implicitly to the interactions which occur between the wearer or user and the product or garment [1]. Evidence supporting such claims generally either does not exist or exists only in industry in-house files (and has not been subjected to scrutiny of the scientific community and thus cannot be considered ½Q1 part of the existing knowledge). The factors that contribute to human performance are multi-factorial and complex. On the surface, human performance in both sport and occupational activity is influenced by physical, psychological, technical, and tactical factors. Under each of these broad categories exist other factors. For example, human performance is influenced by physical fitness and body composition, both potentially interacting with clothing and textile properties (among other factors), to determine the performance outcome. Thus, in some industrial settings, a heavy protective clothing ensemble may impair performance in someone whose aerobic fitness level is low and the impairment may be exacerbated if that person is small with little muscle mass. Similar examples are evident in sport. A triathlete may improve hydrodynamics and increase swim speed by wearing a buoyant wet-suit, but the wet-suit could impair heat loss and put the triathlete at the risk of heat injury during the subsequent cycle or run leg of the event. The swimming skill of the triathlete along with the water temperature may interact with the properties of the wet-suit design and material to influence performance. Thus, determining the effect of clothing and textiles on human performance is difficult because of this multi-factorial nature of performance, and confounding factors cloud much of the literature. In some situations clothing and textiles have a more measurable and obvious effect. For example, in specialised sports such as cycling, aerodynamics is a critical performance factor and the clothing ensemble can have a large impact on the maximal velocity. In other situations where exercise must be performed under adverse environmental conditions, use of appropriate clothing is essential for safe, successful human performance. Extremes in temperature, resulting from exposure to industrial heat sources or working in the tropics or

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desert, create particularly demanding conditions for clothing the individual. Working under pressure (e.g. in diving) or at high altitude introduces other challenges that are not limited to human thermoregulation. Humans now regularly perform tasks under zero gravity where the nature of human movement is severely altered. Innovative clothing may be one method to ensure that health, function, and performance are maintained over the long term in space. Markets for growth of specialised products are evident, and the competition among suppliers is global. Woven and knitted fabrics from high-performance fibres in developing countries are expected to increase [2]. Markets for finished products are becoming more highly specialised particularly in the e´ lite and professional sports and recreational sector. Increased attention is being directed to the performance of the product (e.g. in cycling [3]), although there seems to be less emphasis on the performance of the product user.

1.2 Scope of the Review This review focusses on the link between human performance and clothing and textile products in a variety of situations — work, recreational activities, competitive sport. It has been restricted to research in which evidence of an effect on human performance or factors that directly influence performance have been examined. A clothing/textile orientation has been retained because of the readership of Textile Progress. The placement of some topics lead to inevitable overlapping, and cross-referencing avoids unnecessary repetition. Because thermal effects on human performance are so profound, a separate section on this has been included. The review is structured to include the following topics: (i) (ii) (iii) (iv)

ergonomic requirements, design — garments and products, materials — fibres, yarns, fabrics, finishes, products, and thermal effects.

Each section has a human performance focus. Human performance measures are diverse and are characterised by indices of endurance (work capacity) and/or fatigue, speed, strength, power, range of motion, manual dexterity, motor skill, efficiency, psychophysical response, and thermoregulatory, cardiovascular and neuromuscular indicators of physiological strain (e.g. skin and core temperature, sweat rate, heart rate, integrated electromyography). There are links with the earlier issues of Textile Progress. For example, Textile Progress 22, 2/3/4 Protective Clothing [4] focussed on the thermal properties of materials and garments, including the effects of thermal hazards (primarily flame) on these, and several references on ballistic protection. Little attention was given to the effects of the protective garments on human performance. Textile Progress 24, 4 The Thermal Insulation Properties of Fabrics [5] has a fabric rather than garment focus, with relevance to human performance, comfort, and safety implicit and not linked to measures of actual human performance. Textile Progress 9, 4 Comfort Properties of Textiles [6] focussed on measures of comfort, principally perceptual measures, rather than measures of human performance. Although research on the size and fit of garments was included in Slater’s review, research conducted between the mid 1970s and 2000 needed to be examined and related to human performance. Textile Progress 30, 3/4 Science of Clothing Comfort [7] had not been published at the time of ½Q2 going to press. (Editor to add a comment here.)

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Clothing, Textiles, and Human Performance does not include a review of recent literature on the clothing/textiles items themselves (such as their durability, dimensional stability, heat transfer properties) except where there is a demonstrated effect on human performance. Test methods developed and used for measuring the effects of clothing and textiles on human performance have not been subject to specific critical review and discussion. Readers particularly interested in test methods should consult existing reviews on this topic e.g. [8]. This review does not also include a detailed study of sports aids designed for prevention of injury (e.g. ski bindings, cycling products), medical devices and applications (e.g. sutures, arterial prostheses, customised orthopaedic shoes, and other customised products), or disposable containment suits. By focussing on the interaction between clothing and textiles and human performance it is hoped that this review will stimulate new collaborative research between clothing and textile science and kinesiology (the study of movement).

2. ERGONOMIC REQUIREMENTS 2.1 Background Ergonomic requirements encompass several identifiable and often interdependent variables: for example, product dimensions and their relationship with the wearer/user, shape of the product and the wearer/user, body movement and any changes to this which result from wearing or using the clothing item, and weight of the clothing item and assembly. While these variables are relevant to all types of clothing items, they are most critical in workplace applications where clothing is expected to provide protection against a variety of environmental hazards. Many recent developments in understanding the interactions which occur between clothing and the human body have been the result of research on aspects of workplace protective clothing, but findings from the various studies are difficult to integrate because of confounding influences among variables in many studies. Some of these have been listed (Fig. 2.1) (Adams et al., 1994) as part of an attempt to encourage a more systematic approach to experimental design, so that predicting the effects of clothing on human performance would be possible (Adams et al., 1994). [A garment impediment index (GII) related to personal protective clothing (PPC) was proposed, in which the human performance capability while not wearing PPC was compared with that while wearing PPC (Adams et al., 1994).] However, the need to avoid confounding effects of several variables in research design, and the need to broaden the scope of research beyond that already known such as the links between heat stress and permeability, heat transfer, and ventilation, articulated by Adams [10] remain. Confounding effects cannot always be avoided, but minimising effects of the critical ones can be achieved through careful research design [11]. 2.2 Body Dimensions Detailed measurements on user populations are required for garments and other products not to impair human performance, and this is widely acknowledged (e.g. [12–14]). Body sizes and shapes of various human groups have been studied extensively since about the 1950s. The objectives of these studies have varied (e.g. describing the distribution of disease, describing general health status, establishing sizing for personal protective items), results have been published in diverse literature (e.g. medical journals, journals on industrial health and safety, publications on protective clothing), and methods of measurement have not been identical. Additionally, the reliability of measurement is often poor in anthropometric studies unless properly trained anthropometrists collect the data. Therefore, the use to which

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Fig. 2.1

Number of studies from 118 reviewed which isolated or defined a given garment property and the corresponding dependent measure (Adams et al., 1994)

these data can be applied differs. Key constraints in using body dimensional data are the extent to which: (i) the data are current (i.e. collected within the last 10–15 years), (ii) the data reflect the potential user group (i.e. in terms of ethnic origin, sex, age, occupational activity), and (iii) methods used, particularly the definition of landmarks, are comparable and reproducible. Summaries of comprehensive anthropometric surveys on various human groups and some estimates of dimensions for various body segments such as the hand, the head and the

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foot have been readily accessible since the mid 1980s [13]. Much of the data is derived from studies carried out during the 20-year period from the mid 1960s to early 1980s or on estimates based on these. Most tables provide selected percentile values (usually 5th, 50th, 95th) and standard deviations for males and females separately. Use of this data and estimates become less appropriate as years pass, although the data do remain a valuable resource. Percentile values, while useful for comparing data sets, are not adequate for apparel sizing and evaluation of fit. Dimensions of actual human bodies are not consistent with respect to a particular percentile, i.e. a person whose chest girth is at the 95th percentile may have a measured stature at the 50th percentile. Vertical dimensions are usually more closely correlated among themselves than they are with circumference dimensions. Changes in body dimensions with various stages of the pregnancy cycle, particularly changes in girth, have been documented [15]. Over 50 body measurements were recorded in a sample of 90 women in the working age group (18–40 years) from the U.S.A. Girth dimensions at the hip, waist and bust increased obviously, but so too, did the vertical trunk length, crotch length, and crotch depth. Although 40% of the sample was not able to complete participation in the study for a variety of reasons, the study is one of the few in which the same persons were measured at the same body sites at pre-determined time intervals (i.e. it was a longitudinal rather than a cross-sectional study). Few investigations attempt to monitor changes of the same individuals over time (beyond babies and infants), yet data obtained from doing so would allow for more realistic estimates on body size and shape. [One outstanding exception is the Dunedin Multidisciplinary Health and Development Study in which many aspects of growth and development including a few measures of body size and shape [16] have been followed in the lives of 980 of 1019 surviving New Zealand individuals over a 25 year period (1972/3–2000).] Globalisation of the apparel market, particularly the protective clothing and products sector, along with the adoption of international or quasi-international standards (such as ISO or EN standards) has stimulated groups in several countries to ensure that an adequate description of their various populations is available and used. Two employer groups in New Zealand, obliged to ensure ergonomic principles were applied in the development and supply of protective clothing and equipment, commissioned anthropometric surveys of their respective groups [17–19]. New Zealand fire fighters were found to have vertical body dimensions similar to those from other comparable countries, but different girth dimensions [17,18]; New Zealand forestry workers were found not to reflect the ethnic origin of the general adult population (forestry workers as a group comprising about 33% maori or polynesian ethnic origin compared to about 14% in the general adult population). Some significant differences in body dimensions between the maori/polynesian group of workers and the caucasian group were observed (the former generally shorter, and with some greater circumference measurements) [19]. Physically demanding occupations no longer comprise exclusively male employees. For example, prior to 1975 less than 3% of the New Zealand Police Service comprised females, but by 1998 approximately 16% of the workforce was female [20]. Therefore, work clothing designed from historical anthropometric data of a largely male workforce may not appropriately fit female workers employed at any present time. Nineteen sites of the hands of 380 Canadian agricultural workers were measured, summarised (although the summary appears to be restricted to a thesis document [21]), and selected percentile values compared with those of military personnel in Canada and the U.S.A. [22]. No significant differences between the Canadian agricultural workers and the Canadian

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aircrew were found, although there were significant differences between Canadian agricultural workers and the U.S.A. military, again illustrating problems inherent in using data from one population group as the basis for sizing products (in this instance gloves) for another group. Improvements in the accuracy of estimates of selected body dimensions from others (e.g. body stature estimated from foot dimensions) continue to be sought for forensic [23] and other applications. Accuracy improved when both foot length and breadth were included, as well as race/sex indicators (although the race/sex variable made only a slight improvement). Height could be predicted to within  86 mm [23], confirming the comments about the generally weak relationship between vertical and girth (breadth) dimensions and the desirability of taking ethnic origin into account.

2.3 Product Sizing and Fit 2.3.1 Fit and its Evaluation Fit, however defined (static fit ‘the relationship between garment size and body size’, dynamic fit ‘whether a garment allows the body to perform usual tasks without garment interference and resistance’ [22]), is evaluated using rather coarse grading scales. These scales depend on visual evaluation and perceptions of pressure on the body of the wearer/user, and visual evaluation of an external assessor. Tests for fit may be static (the wearer remains in one position) or dynamic (the wearer adopts a range of movements or positions usually selected to represent those relevant to the activity for which the garment and/or product is worn). Dynamic fit is most relevant to this review of the effects of clothing and textiles on human performance. (Product styling and design ‘ease’, such as that in folds and gathers of cloth, directly affect the dimensional differences the body and the garment. The two types of ease (that required to cover the body simply with material and that required to achieve a particular design/style effect) are confounded in many investigations. Discussion of design/ styling has been included in Section 3, and other aspects of ease are discussed as an ½Q3 ergonomic factor.) General procedures for evaluating or testing the fit of garments and/or products to the wearer were outlined during the mid 1980s [24]. These included the following. (i) Selection of participants sized to reflect 90–98% of the body size variability for the anthropometric variables of interest. Use of bivariate frequency tables for the key variables was suggested. (ii) Collection of basic information on the participants (e.g. age, sex, work experience) and sensory aspects (e.g. quality of fit, ability to perform functions). (iii) Recording of dimensions and location of each participant’s ‘position’ on the bivariate table. (iv) Participants adopting various positions/movements to simulate use, while investigators recorded, noted, photographed. (Kinematic techniques used typically in biomechanical studies of human movement would be particularly appropriate.) (v) Use of percentile and bivariate charts to monitor appropriateness of the sample and to modify collection of the sample as required, targetting a specific category, then comparing descriptive statistics from the sample with those of the population. (vi) Analysing the responses of wearers on perceptions of fit. Existence of relevant data on body dimensions and thus the possibility of creating relevant bivariate frequency tables is assumed, although such data may not be available.

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An evaluation of static fit on 38 participants of four types of gloves for agricultural workers identified that dimensions of the glove fingers were typically too long and/or too loose [22]. (Hand dimensions of participants in the fit test were representative of those in the user group, having been confirmed by comparing mean dimensions and standard deviations of key sites.) The thumb of the glove was considered poorly located, with the crotch of the thumb not sufficiently deep. Gloves made from thinner materials were more acceptable than those from thicker materials (over the range evaluated 0.30–0.55 mm), although thickness was less of an issue when the material from which the glove was made was flexible [22]. Results of an evaluation of dynamic fit undertaken by Tremblay appear to be restricted to the thesis document [21], although glove ease which optimised manual dexterity was defined [9]. (See Section 3.) As part of a comprehensive review of human factors (including fit) and clothing for cold conditions, compromises among material thickness, maintenance of adequate hand temperature under cold ambient conditions, and maintenance of manual dexterity were articulated [25]. Glove configuration reportedly adversely affected manual dexterity, with mittens having the most detrimental effect [25], and grip strength reportedly decreasing with wearing gloves (rubber, leather, bare-handed conditions) [25]. Changes to worker mobility attributable to differences in garment/product size or design have been measured using several procedures (goniometer, Leighton Flexometer, electrogoniometer, perceived impediment, comfort) [26]. Three sizes of one style of overall each made from three different weights of fabric [sized as appropriate, smaller, larger; 144.08 g/m2 (4.25 oz/yd2) for a 65%/35% polyester cotton fabric, 245.78 g/m2 (7.25 oz/yd2) for a 50%/ 50% polyester cotton fabric, 339.0 g/m2 (10 oz/yd2) for a 50%/50% polyester cotton fabric, respectively] were worn by 10 male participants. As the range of motion possible decreased with the variously-sized garments, participants (not surprisingly) reported increased restriction in their movement. No attempt was made to identify what aspects of the garment resulted in restriction or deteriorating levels of comfort, acknowledging that results from more than 10 participants would be required for this. Inclusion of more information on the design of this experiment and the procedures for statistical analysis would have been useful. For example, each participant completed all trials but it is not clear if the sequence for testing was randomized among the participants. Adequate replication seems to have been a problem. Calculating separate correlations between data from each of the methods for each ½Q4 of the nine body movements does not seem to be the most appropriate form of analysis.

2.3.2 Garment Sizing Garment sizing for groups of workers and sports persons is more critical than garment sizing for fashion/dress for several reasons: first, lengths and widths of protective/specialised garments cannot be altered easily because the procedures and equipment required are not usually immediately available. Second, precise fit of protective/specialised garments or products is required for them to function satisfactorily which is not the case for fashion goods. Third, inadequate fit can result in impaired performance and increased exposure to a hazard. In sporting endurance events, friction injuries and chafing from inadequate fit can cause discomfort and impair performance, and in sport requiring protective gear such as American football or ice-hockey, inadequate fit may not only increase the likelihood of injury but may also impair the range of motion and performance. Traditional sizing practices in garment manufacture involve selecting a middle size and grading up or down. The underlying assumption is that if one dimension is larger (or

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smaller) then all other dimensions are also larger (or smaller). More appropriate sizing can be achieved by selecting (at least) two dimensions important in the item and, after arranging data of relevant participants, establishing size demarcations as recommended values [27] (Fig. 2.2). The design is developed for those people in each category, not scaled up or down.

Fig. 2.2

A bivariate frequency plot of stature and weight values with an eight-size system displayed (Robinette, 1986)

Despite limitations, Robinette’s method [27] has provided a useful technique for developing a sizing system integrated for male and female members of the U.S. Army [28]. Conventional grading (in this case, down-sizing patterns for males) would not have taken into account sexual dimorphic body proportions. The resulting size system contained roughly three groups (female only, mixed, male only) when body dimensions of the sample were positioned (Fig. 2.3). (See Section 3.2.1.) Improved ways in which body dimensions can be used to determine appropriate garment dimensions were developed with readily accessible complex statistical operations [18]. Applying principal component analysis to comprehensive data sets of body dimensions overcomes the need to make assumptions about which particular variable (or two variables, in the case of bivariate frequencies) accounts for most of the variability in the sample [18]. (Table 2.1 [18] provides an example of factor analysis based on principal components for various body sections of part of the New Zealand male workforce.) Use of k-means clustering techniques [29] allowed good estimates of dimensions for each site to be made (Table 2.2) [18]. Optimising as a means of developing a sizing system for the U.S. women’s market has been based on a mathematical description of the goodness of fit experienced by an individual when wearing a garment [30]. In this work, garment fit was captured by a measure of distance calculated from the difference between the person’s dimensions and that of the prototype for that size [30]. Aggregation of all individuals’ distances from their assigned size was the measure of how the sizing system performs in fitting the population [30] (Fig. 2.4). How particular sizes are designated is another issue relevant to domestic and international markets, but one which is far from being resolved because many countries wish to retain their own matrix of measurements, usually based on different data sets (e.g. [31]). There is also an inherent danger in insistence in adopting international or quasiinternational garment sizing dimensions however much commercial activity might be simplified by doing so.

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Fig. 2.3

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A 20-size system for the battle-dress uniform trousers (1 inch=25.4 mm) (Gordon, 1986)

2.3.3 Restrictions in Reach, Body Motion, and Manual Dexterity The fit of a garment which envelops the body completely, such as a gas protection suit, is particularly important because garment slip is not possible with routine body movements. (Garment slip is the term for sliding of a garment section from the surface where it is normally positioned in response to body movement, e.g., sliding of trousers at the waist and ankle as the wearer adopts a seated position. The term was first used in the early 1980s [32].) Dimensions of the user population both when standing and in body positions typical of end-use thus need to be taken into account. Mobility of wearers in prototype suits was adversely affected by tightness in the crotch and knee of suits, incorrect sleeve and flange proportions, manual dexterity by gloves shifting away from the hand, and the hood adversely affecting vision [33]. However, the comparative dimensions of wearers and garments involved were not reported [33]. The issue of mobility has particular relevance to sport. For example, even when garments are custom fitted, most body dimensions are obtained on persons in the standing position. For a cyclist who competes sitting on a bike with extreme hip flexion, the standing fit may translate to a poor fit in the more prone, exercising position. As part of a full battery of tests on protection against chemicals, twenty U.S. fire fighters wore three different ensembles under controlled conditions in order to determine restrictions in reach and body motion [34]. Baseline measures were obtained with fire

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Table 2.1 Principal Components for Body Sections (Decreasing Order by Coefficient Size) Head — total variance explained by three derived factors 95.9% (n=682) Upper head 54.5% (Head depth) (Head girth)

Head breadth 21.3%

Face length 21.1%

Hand — total variance explained by three derived factors 88.5% (n=683) Hand length 56.9% (Palm length) (Hand length)

Hand breadth and girth 19.1%

Lower upper limb girths 12.5%

Foot — total variance explained by four derived factors 88.4% (n=681) Lower limb girths 49.4% (Calf girth) (Ankle girth)

Foot dimensions 18.7% (Foot breadth) (Foot girth)

Lower limb lengths 11.2% (Tibiale height) (Foot length)

Ankle height 9.1% (Ankle height)

Lower torso — total variance explained by four derived factors 86.0% (n=675) Lower lengths 50.3% (Crotch height) (Waist height) (Tochanterion height) (Knee height) (Popliteal height) (Stature) (Tibiale height) (Buttock–knee length) (Buttock–popliteal length)

Lower trunk girths 26.4%

Lower limb girths 5.1%

Ankle height 4.2%

Upper torso — total variance explained by five derived factors 75.8% (n=672) Upper torso girths

Upper limb lengths 18.4%

39.8% (Chest girth) (Waist girth) (Anterior–posterior chest depth) (Transverse chest breadth) (Weight) (Arm girth relaxed)

Torso lengths 7.0%

Shoulder breadth 5.6%

Hand/wrist girth 5.0%

Total body cover — total variance explained by four derived factors 72.2% (n=654) (excluding head, hands and feet) Lengths/heights

Weight/girths

42.5% 20.5% (Crotch height) (Spinale height) (Knee height) (Waist height) (Trochanterion height) (Popliteal height) (Tibiale height) (Shoulder–elbow–wrist length) etc. (12 others including stature) From Laing et al. (1999).

Torso proportions 5.1%

Shoulder breadths 4.0%

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Table 2.2 Foot Covering: Typical Size Chart* Number of existing footwear sizes Solution Tolerance Centre of size Range of size Approximate % of sample fittedy % of sample fitting more than 1 size % not fitted (outliers) Body dimensions Ankle girth X 5% 95% Ankle height X 5% 95% Foot girth X 5% 95% Foot breadth X 5% 95% Tibiale height X 5% 95%

11 8 sizes (but recommend one further size at each end to accommodate all employees) 10 235 245 255 265 275 285 295 305 230–240 240–250 250–260 260–270 270–280 280–290 290–300 300–310 ,1 10

5

18

33

31

17

5

,1

218 198 243 130 109 148 254 234 273 100 92 109 421 382 467

224 207 242 132 116 151 261 243 281 104 93 113 430 395 461

228 211 246 135 119 153 266 249 284 106 97 114 442 409 469

231 215 250 139 123 156 271 254 289 108 98 117 454 422 489

238 220 260 142 127 158 277 263 299 111 103 120 463 432 496

240 221 261 144 127 158 280 264 301 112 101 121 481 443 518

236 — — 147 — — 281 — — 111 — — 508 — —

1 222 — — 127 — — 258 — — 104 — — 412 — —

yRounding errors mean that the total is not always 100%. *Based on foot length; mm body dimensions unless specified. From Laing et al. (1999).

fighters in shorts and T-shirts — nine movements associated with joint changes (in degrees) were measured (using a Leighton Flexometer), and three reaches were measured with an anthropometer. Overhead reach was reduced when wearing each of three brands of fire fighting ensembles with self-contained breathing apparatus (SCBA) (2.2–8.7% for one hand; 2.5–10.8% for two hands). The ability to perform in the bulky ensembles was thus shown to be impaired, and multiple sizing of suits recommended as a means of minimising this [34]. The effects on the wearer’s mobility of garment ease in one area of a garment while controlling ease in all other areas have also been investigated [35]. Five male participants wore protective overalls with different amounts of ease and locations of crotch ease. The effects on mobility during an exercise protocol was determined (measuring the range of motion possible with a Leighton Flexometer). A factorial experimental design (randomised, complete block, repeated measures) was used: the control was a garment sized to provide constant vertical trunk ease (107 mm) for each participant, and the test garments with added vertical crotch ease (170  10 mm) all at the garment back, or part in the back and part in the front of the overall. Body movement was maximised when vertical ease was added to the back only [35]. Wear trials (27 h of continuous wear) conducted under controlled conditions (four separate test sessions to determine physical performance) using eight male participants and three clothing conditions have demonstrated some adverse effects of protective clothing on human performance [36]. Trunk flexion, strength of grip, vertical jump height, a stepping

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Fig. 2.4

Textile Progress

Optimisation of body dimensions for development of sizing systems (Ashdown, 1998)

exercise and an obstacle course were included in the protocol. Performance was shown to degrade in all tasks when protective clothing was worn. Heart rates were significantly higher when an impermeable overall was compared with other garments worn in stepping [36]. Interestingly, performances in some routines (e.g. stepping, obstacle course) were better after 24 h than they were initially. This was attributed to familiarisation, a possible reduction in emotional stress, and differences in motivational levels [36]. Such effects need to be taken into account in experimental design and analysis. Garments designed and sized for males pose problems for females who may be required to wear them, such that the physical performance of the females may be impaired. Optimising human performance while continuing to use ‘unisex’ garments which complied with a proposed standard for limited-use protective overalls has been investigated [37].

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Garments which complied with the proposed standard were manufactured by three different suppliers, 25 garments each, in a range of sizes, all in the same non-woven spunbonded olefin (Tyvek2) but with various sleeve styles/designs representing each manufacturer’s usual production (i.e set-in, raglan, yoke with sleeve cut in one). Evaluation of the fit of garments under static and dynamic work-simulation conditions was undertaken by a group of participants representing the user group (n=166 males and females, six racial groups, from the agricultural sector) with an appropriate number of participants in each size category. Only about half of the participants considered that the garment worn fitted well (51%), and that it allowed them to perform the tasks easily (61%) (results for all sleeve designs were pooled). Most participants sized for and evaluating the smallest garment size considered it too large. As the garment sizes approached each end of the scale, the fit was judged as poorer (i.e. smaller and taller people not being simply scaled down or up versions of the average). Garments with raglan sleeves had a longer body than the others and this was considered to explain the significantly poorer level of satisfaction with that style. The sleeve design itself may have had an adverse effect, although the authors do not suggest this possibility. (Statistical tests including analysis of variance were carried out, but whether these were parametric or nonparametric tests were not stated and the tables of results do not provide the necessary information.) Nevertheless, this paper [37] illustrates how garment fit might be improved prior to mass production, and perhaps more importantly, prior to publication of dimensional requirements as part of a standard. As the proposed standard required a minimum size, anything above that would have complied irrespective of whether or not the excess dimensions compromised performance. Both a minimum and maximum measurement were recommended as the substitution requirement. The amount of ease required inside a chemical protective glove to enable effective functioning of the hand and comfortable fit has been determined using four tests of manual dexterity (the Minnesota Rate of Manipulation Turning Test, the O’Connor Fine Finger Dexterity Test, the Cord Manipulation and Cylinder Stringing Test, and the Magazine Loading Test), along with a questionnaire [9]. Variations in fit of the glove styles were achieved by having each of the participants (n=24 males) select gloves of the ‘best fit’, then assigning that size, one size larger and one smaller, for the trial. A glove liner manufactured from a blend of cotton, viscose, and an elastomer was used in the appropriate sizes to achieve the fit variations required in the experiment. Six fitting conditions were evaluated: three gloves, one in each of three sizes, and each with and without a liner. The order in which participants completed the tests was randomised, and participants had practised the tests several times before evaluating the fit and having their test performance measured. In general, dexterity was found to be consistently better when either the unlined, smaller-fitting glove or the unlined best-fitting glove was used. Moving from the best-fitting unlined glove to the smaller-fitting unlined glove did not significantly enhance or degrade dexterity. However, moving from the best-fitting unlined glove to the larger-fitting unlined glove resulted in significantly slower performance times in two of the four tests. Manual dexterity and/or speed for completing tasks was optimised when the glove was considered the ‘best fit’ or was one size smaller, but impaired when the glove was one size larger than what was considered the ‘best fit’. Ease at various parts of the glove was calculated from dimensions of the glove and the corresponding position on the wearer’s hand (hand girth, girth of digits two and four, and digit lengths). Thicknesses of the glove and liner materials were subtracted from the

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glove outer dimensions as appropriate. Negative ease was observed for digit length and girth (length  3.5 mm, girth  1.9 mm) and positive ease for palm girth ( þ 17.5 mm). While these values were specific to gloves in this particular study, or possibly to other gloves with similar properties (i.e. vulcanised chloroprene and butyl rubber, shaped to conform to each of the left and right hands, 0.79 mm thick, and liner 1 mm thick), the fact that both positive and negative ease existed in different parts of the same product was noted [9].

2.4 Weight 2.4.1 Weights of Garments and Garment Assemblies One of the few early investigations of the effect on energy cost of multiple layers (and implicitly weight) showed that mutiple-layering of clothing increased the energy cost to the wearer when walking by about 16% [38]. Since then, surprisingly little evidence of differences in human performance attributable to differences in the weight of garment assemblies worn has been published, although weight continues to be confounded with other product variables (e.g. [39,40]). Nevertheless, minimising additional weight of protective garments in order to maintain normal human performance is a well-recognised ergonomic principle, particularly for development of workplace protective clothing [41–43], and to a lesser extent, clothing for sport and recreational activity. In sport, more attention has been directed at improving sporting equipment (e.g. the performance:weight ratio of bicycles [44]) and the design of back-packs [45] than investigating the effects of clothing weight on performance, or in the re-design of sporting equipment. Studies in which the influence of clothing weight on sport performance has been investigated have generally been inconclusive (e.g. [46]). In many sports activities involving running (weight-bearing), gravity is a major force to overcome. As a result, excess weight can be detrimental to the running performance [47]. Body mass, not increased clothing weight, has been the focus of these studies. Excess weight in any form may not necessarily be detrimental to a weight-supported activity such as cycling provided the frontal surface area is not increased (which would decrease aerodynamics). Nonetheless, the influence of increased mass on cycling performance would depend somewhat on the topography of a cycling course, a hilly route expected to increase the effect of gravity on the cyclist [48], which may be disadvantageous for a heavy [47] or ½Q5 heavily-clothed athlete. Definition of the maximum acceptable weight of clothing products has been attempted in several studies. For example, the maximum weight of an industrial helmet is claimed to be under 300 g [43], although limited supporting data seem to have been presented. Weight limitations for various parts of a (then) new generation self-contained atmospheric protective ensemble for the Kennedy Space Center were set at 11.3 kg for the outfit, 18.6 kg for the environmental control unit, and 2.94 kg for the emergency air supply [49] (total 32.84 kg). These limits were presumably based on extensive experimentation and observation, although relevant details again appear not to have been published. Energy expenditure is reported to increase by 1.2% for every kilogram of additional ½Q6 weight of personal protective dress [50] (presumably given all other constant conditions). In a more recent study, an external load of 31.5 kg or 49.4 kg significantly increased energy expenditure above that of unloaded (clothing mass 5.2 kg) sub-maximal treadmill walking by 10–18% [51]. Additionally, in this study participants walked for 50 min, and the authors concluded that the predictive formula of Pandolf et al. [50] underestimated the actual

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metabolic cost during the final minute by 10–16% as a result of energy expenditure drifting higher over the course of the walk. No metabolic drift was observed in the unloaded condition. Changes in garment assemblies have also been shown to alter energy costs to the wearer. The energy cost of wearing CPC and the relative contribution of the mask required have been quantified. The oxygen uptake and ventilation of 14 soldiers while walking on a treadmill with increasing grades (0, 5, 10%) each for 20 min was monitored. Three garment conditions were evaluated (battle-dress only, mask only, and CPC including the mask) [52]. The mask induced hypoventilation, although oxygen uptake was not affected at exercise intensities up to 60% of VO2 max. And most recently, the oxygen consumption (n=9, 5 females, 4 males) of walking unloaded and loaded (25.6 kg in each of two back-pack designs) was significantly higher when treadmill walking at various uphill and downhill gradients ½Q7 while loaded [45]. Oxygen consumption was significantly lower (by about 5%) when the redesigned back-pack was compared with the more traditional design [45], demonstrating that load can be carried with less adverse effect on human performance when distributed between the back and front trunk [45]. Maximal physical work performance of 12 healthy male fire fighters has been assessed while either not wearing or wearing typical fire-fighting ensembles. The ensembles complied with EN 469 [42] and included a self-contained breathing apparatus (total mass 25.9 kg). The fire fighters walked on a treadmill in a thermally-neutral environment until volitional exhaustion [53]. Maximal working time and walking speed of the participants were reduced by about 25% with the fire-protective ensemble/equipment, the reduction being attributed primarily to the extra mass of the ensemble/breathing equipment [53]. Multiple layers of protective clothing including a chemical defence uniform with body armor and load-bearing equipment have been shown to impose an external impedance to respiration (in addition to that caused by the chemical–biological protective mask also worn) [54]. The mechanics and patterns of breathing along with sensory responses of 15 U.S. Army personnel during rest and sustained exercise were recorded. Although heat strain experienced by the participants as a result of wearing the clothing ensemble during exercise and rest was minimal, some respiratory impairment was evident, and this was attributed to the chemical defence uniform. Possible additional effects were acknowledged. (‘These impairments to ventilation may provoke more aversive effects than the larger resistive loads imposed by the chemical–biological protective mask’) [54]. Dissatisfaction with excessive weight (and noise) of air-supplied, one- and two-piece butyl chemical protective suits was reported during the mid 1980s [55]; so refinement of products for this purpose required a reduction in garment weight (6.4, 4.3, 2.0 kg for the two, one-piece butyl, and Saranex-laminated Tyvek, respectively), with a 1.1 kg ventilating vest [55]). Unfortunately, the wearers’ (the number involved was not reported) responses to weight seemed limited to informal perception-based oral reports, details of which were not published. Wearing the lightest-weight athletic clothing, distance running by amateur athletes was not improved markedly [46]. Stevens concluded ‘The weight of clothing is not considered to be an important factor in marathon running speed’ [46]. However, if the marathon was performed on a hilly course, then a small increase in weight could have a substantial effect because of the increased work required against gravity.

2.4.2 Distribution of Weight and Objects on the Body Distribution of the weight of garments/products or objects that form part of an assembly is the underlying theme of several patented developments. For example, improved physical

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performance of athletes and/or other users has been claimed in two such developments: one [56] was a cover for footwear made from ‘stretch’ fabric, with pockets into which weights are placed, and with use is claimed to improve ‘speed, strength and endurance’ of the lower limbs, and to improve on ‘certain neuro-musculoskeletal disorders resulting from weakness of the lower limb’; and the second [57] was a vest with pockets into which weights were placed, but arranged so the weight was carried around the wearer’s mid-section rather than at the shoulder area, and which is intended to improve the physical performance of jumpers and runners (as well as other categories of wearers). Whether any evidence exists for the validity of the claims made for either product is not clear. Other products have been developed to re-position the centre of gravity of the body. For example, the effects of sprint and strength training with ‘Strength shoes 2’ have been reported. These shoes are modified athletic shoes with a 40 mm thick rubber (usually) platform attached to the front half of the sole which have been promoted as effective training aids to help overload the neuromuscular system during training leading to enhanced strength, speed, power, and calf flexibility. They were designed to overload the calf muscles by shifting load distribution to the front of the foot. No enhancement of flexibility, strength or performance was reported in intercollegiate track and field athletes after 8 weeks of training with this product [58]. In another study, 72 college-aged males were randomly split into a control group, a Strength shoe group or a regular shoe group. After 10 weeks of training no significant differences between groups in the training response were observed, but 7 members from the Strength shoe2 group had dropped out of the study because of injury compared to only 1 drop-out reported from the regular shoe group [59]. Thus, these weighted shoes do not seem to provide any extra training benefit over regular athletic shoes, but do seem to put the athlete at the increased risk of injury due to altered biomechanics (See Section 3.4.2.).

2.4.3 Effects of Reduced Gravity In microgravity, the weight of clothing is of little consequence. In fact, the absence of load on the body results in significant physical and physiological deterioration in the form of reduced muscle and bone mass, reduced strength, and reduced aerobic capacity among other things [60]. Innovative clothing designed for use in microgravity may be one method for counteracting the physiological decrements experienced during prolonged space-flight. An example of a clothing countermeasure is the ‘Penguin’ suit used by Russian crews during an 8–12 hour workday in space. This suit has rubber bands incorporated into the fabric extending from the shoulders to the waist and from the waist to the lower extremities. These bands provide resistance during movement and are designed to protect against musculoskeletal atrophy by providing loads comparable to approximately 70% of the gravitational force exerted on the body mass on earth. No quantitative assessment of their efficacy has been reported [60]. Exposure to reduced gravity is also associated with a loss of gravitational blood pressure gradients which cause fluid shifts from the lower extremities towards the head. These welldocumented fluid shifts may cause deleterious endocrine and cardiovascular effects [61]. Suits or equipment providing lower body negative pressure combined with exercise have been proposed as useful countermeasures during space-flight. They may help to maintain normal gravitational blood pressure gradients and minimise the shift in blood and tissue fluids from the legs towards the thorax. There are possible side-effects of using lower body negative pressure devices during space-flight, including syncope, herniae and cephalic fluid shifts after the lower body negative pressure is released [61]. Anti-gravity suits that provide

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lower body positive pressure are certainly worn by the majority of astronauts returning to earth after prolonged space-flight as one means of reducing orthostatic intolerance caused by the reduced capacity of the circulatory system to regulate blood pressure. Anti-gravity suits also have clinical applications, e.g. to assist human performance in people with spinal cord injury to help compensate for the lack of neural regulation in regions below the spinal cord lesion, and to increase venous pressure. The increase in pressure provokes an increase in venous return, which positively affects the cardiovascular responses in persons with spinal cord injury during upper-body exercise [62]. The application of pressurised anti-gravity suits to the lower extremities has been shown to diminish venous pooling below the lesion level in people with spinal cord injury [63], and displace blood centrally from the lower extremities and abdomen into the heart, brain and lung circulation [62–66]. Reports of mobilising up to 30% blood volume [66], 750–2000 ml of blood [64,67], have aided in increasing stroke volumes by 14% [64]. Such a large displacement of blood would in turn enhance perfusion of the vital organs and alter cardiovascular parameters [62– 64,68]. Blood pressure has been shown to increase generally [63,67,69], while heart rates tend to decrease after suit inflation. Reduced heart rates are believed to be a response of an increase in stroke volume and blood pressure [67]. The application of anti-gravity suits appears to be more effective in spinal cord injured persons over those who are able bodied [62], and in sub-maximal over maximal arm crank exercising parameters [63]. Two explanations for the non-concomitant increase in maximal performance have been proposed. First, the aerobic and anaerobic contribution to maximal exercise seemed not to be influenced by the circulatory benefits of lower extremity pressure, suggesting that the limitation in maximal oxygen consumption was located peripherally in the oxygen delivery or the oxygen consumption of arm musculature. Second, an increase in heart rate may act as a limiting mechanism for further stroke volume enhancement when close to maximal exercise levels, despite the central haemodynamic benefits of lower extremity pressure [63]. Training status appears to alter the effectiveness of the anti-gravity suit. Well-trained persons may have already reached their limits in several aspects related to maximal oxygen consumption, whereas in untrained quadriplegic persons, the central circulatory adaptation may be the most important limitation to maximal oxygen consumption [63]. Guezennec et al. [65] demonstrated a pronounced effect of exercise on catecholamine concentrations, but their data ruled out any effect from pressure-suit inflation on catecholamine concentrations. Prolonged inflation of the suit at high pressures has been shown to cause metabolic acidosis [66] and compartmental syndrome [63] as a consequence of poor perfusion of the lower extremities and the expected anaerobic metabolism. Abdominal discomfort and pain have also been observed at high pressures [64], and on normal persons, complaints of headaches and a fear of producing an intracranial haemorrhage have been reported [64]. A safe maximum pressure appears to be 52 mm Hg [63]. Of the devices aimed at preventing circulatory complications in persons with spinal cord injury, neither leg bandages nor tight abdominal binders have proven to be particularly successful. Neoprene-impregnated nylon trousers and the inflatable anti-gravity suit have shown promise, but fault in their cost and practicality [68].

2.5 Summary In summary, human performance can most certainly be impaired by poor fit, restricting factors such as range of motion, reach, and manual dexterity. More anthropometric

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research is required to describe population body dimensions and aid in product sizing, and employers/administrators need to be aware of likely differences in fit requirements of workers/athletes as a result of differences in sex, ethnicity, and age. Further longitudinal anthropometric studies would yield extremely useful information, as would further analysis of existing data to determine relationships among dimensions of various body sites (so that more accurate predictions of dimensions might be obtained). Additionally, although surprisingly little research seems to have been directed at the effects of weight of garments and assemblies on human performance, excess weight of clothing has been shown to be detrimental to performance and results in increased energy expenditure for a given work rate. The extent of impairment of performance as a result of excess weight will depend upon the specific task, such that greater impairment would be expected in weight-bearing tasks. The weight of clothing is not an issue for humans working in zero gravity but innovative clothing designs which provide extra resistance to muscular movement through their elastic properties, or alter the blood pressure gradients that are largely lost in space, may be important counter-measures to the deconditioning that occurs in prolonged space flight. Some of the garment assemblies initially designed for military use also have clinical applications and may improve function and performance during exercise in people with spinal cord injury for example. The ergonomic principles of optimising fit, reducing weight of the garments or garment assembly, and altering the physical stress of performing a task through innovative clothing design remain central to optimising human performance, but there is a paucity of wellcontrolled research in this area.

3. DESIGN — GARMENTS AND PRODUCTS 3.1 Background Several approaches to designing apparel products and systems which enhance human performance were described during the 1990s: used (and sometimes failed) garments have been examined [33,71], injuries sustained by wearers which resulted in hospital stay have been identified and described (e.g. [72–74]), and the processes of designing both sophisticated and other clothing assemblies described (e.g. [33,49,75]) usually including wear testing of the final products (such as determining physical performance under controlled conditions (e.g. [36]), or field trials (e.g. [76]), or theoretical finite element modelling (e.g. [77]). A comprehensive review of the effects of wearing chemical protective clothing (CPC) on aspects of military performance was published in the late 1990s focussing on psychophysiological stresses which occur to personnel [78]. 3.2 Positive and Negative Garment Styling Ease, and Compression Ease is defined as the difference in dimensions between the body site and the garment/cover at that site, and may be positive or negative (where dimensions of the garment exceed or are less than those of the body, respectively). What constitutes optimal ease is difficult to define, because properties of the constituent materials, the conditions in which the garments are worn, the function of the garment, and desired styling/design effects all vary. (See Section 2.3.) 3.2.1 Positive Ease Effects of selected task-related movements on limited-use coveralls for asbestos removal operators were examined using a series of body movements typical of the work carried out [79]. (Although not stated by the authors, the evidence on which the findings of the study

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were based related to stresses exerted by the human body on the garments and the objective was to improve garment performance rather than human performance.) Participants experienced in the building trades (n=5 males) wore one of three coveralls with vertical, horizontal or diagonal slits (313 mm), spaced 25 mm apart on three separate occasions [79]. Strains on the garments resulting from adoption of different body positions were made visible by the participant wearing a dark undergarment, and were quantified by examining video recordings of the various body movements. This information was used to define the amount of additional ease to be added at several garment sites (e.g. the back of the sleeve armscye, wrist, back of the torso, knee area at inside leg seam, front of leg and foot, back of hood) (Fig. 3.1). A refined design was field-tested (n=17 asbestos removal workers) with fewer tears in the garment caused by extreme body movement evident. The influence of clothing fit on sport performance has been examined in a limited number of studies and the experimental design has been flawed in several of these. As an example, one group attempted to determine whether wearing loose-fitting shorts or tight-fitting shorts influenced the physical and psychophysical response to sub-maximal treadmill running [70]. However, the garments were made from different materials (nylon, elastomeric (Lycra), garment weight was not reported, and neither was any description of fit. Fit also seems to have been confused with design and styling. Not surprisingly, no performance difference was identified between loose- and tight-fitting shorts. Garment design/styling (sometimes incorrectly referred to as fit) can affect human performance by influencing aerodynamics (aerodynamics being of critical importance to performance when velocities of movement exceed about 5 m s). This has been demonstrated in a number of sports including running, cycling, downhill and cross-country skiing, bobsled, luge, and speed skating, and in the worst case scenario it has been estimated that drag may be reduced by up to 10% through the appropriate use of clothing [80]. (See Section 3.5.1.) Similarly, wet-suits can have a marked effect on changing buoyancy and drag of the swimming body and because of their performance benefits, their use is now closely regulated in events such as triathlon. (See Section 3.5.2.) The influence of wet-suit use on swimming performance was the subject of review in the mid 1990s [81]. Closeness of fit (a tight-fitting crew neck undergarment compared with a loose-fitting shirt, as part of a commonly used clothing ensemble) has been shown to affect skin cooling [82]. Exposure of males (n ¼ 10) to simulated packing work under three ambient conditions (208C, air velocity 0.45 m/s, 0–30 min; 58C, air velocity 0.39 m/s, 30–60 min; 58C, air velocity 1.23 m/s, 76–90 min) wearing each of the two undergarment fit simulations (tight and loose), resulted in higher torso and arm skin temperatures observed when the tight-fitting garment was worn [82]. Additionally, sweating tended to begin earlier and skin wettedness tended to be higher with the tight–fitting garment than with the loose-fitting garment [82]. However, no differences were observed in core temperature, heart rate, or perceptions of thermal conditions [82]. This is interesting, as the net effect of the larger air space under the garment appeared to be one of reducing rather than increased thermal resistance (assuming all other variables were constant).

3.2.2 Negative Ease and Body Compression Bras for sections of the sports market in which breast displacement of participants occurs are usually designed on the principle of compressing breasts toward the body, spreading their weight more evenly across the rib cage, and distributing the pressure of the bra relatively evenly on the body (e.g. [83]). Whether or not this strategy was successful for

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Fig. 3.1

Textile Progress

Locations of stress on coveralls (Ashdown and Watkins, 1992)

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participants (n=59 females) whose cup size varied over the range A–D was examined by quantifying cinematographic records of participants jogging on a level treadmill at 9.66 km/h (6 miles/h) first nude, then with one of seven types of sports bras, each person repeating the routine wearing each bra [83]. Vertical displacement was best controlled by bras which tended to flatten the breasts, holding them close to the body’s centre of gravity, although these bras were not rated well in perceived comfort. Minimising breast displacement was considered the key design criterion for bras for large-breasted women, but not so important for small-breasted women. Whether breast displacement affected jogging or other physical performance of the wearers was not investigated. Pressure covers designed to reduce arm pain experienced by pilots during flying, assumed to be caused by fluid pooling in the arm, have been shown to be effective. Four designs configurations (an elastomeric T-shirt, a gel wrap, elastomeric bands, a gel shirt), were tested in a series of runs in a dynamic flight simulator, using civilian pilots (n=7 males) [84]. Improved dynamic flight simulator performance was observed when using each of the four designs over the ‘bare’ condition (no cover, control condition). User rankings of the four designs in terms of effectiveness of pain reduction at the end of the study however, did not correlate significantly with the pain levels reported during dynamic flight simulation [84]. Pressurised sleeves and gloves (40, 60, 80 mm) have been shown to be effective in reducing pain experienced by wearers (n=8 healthy male volunteers in simulated aerial combat manoevres) when compared with not wearing such products, although no significant differences were detected among each of the three different pressures [85]. Heart rate was not significantly affected by any of the wearing conditions [85]. From the practical perspective of designing and manufacturing products, maintaining even pressure at the skin surface/pressure garment interface is not possible when the pressure garment is manufactured using cut and sew procedures (rather than as a weft-knitted cylinder), because of hem effects [86]. Interface pressures from a laboratory model were in the range 10–28 mm Hg, the higher values at positions 50–75 mm from the hem edge and where the negative ease was  30 to  35% [86]. Whether comparable differences should be expected on human skin/garment interfaces is not clear. The effects of compressive garments on various aspects of human performance attracted attention during the 1990s. Compressive garments have been traditionally used to decrease venous stasis and increase venous blood flow in both individuals with peripheral vascular disease and those with normal vascular systems [87,88]. The increased venous return observed with compression stockings has been suggested to result from the shunting of blood to deep veins as a result of the compression of superficial veins and improved capillary filtration. Berry investigated whether compression stockings or elastic tights change the physiological response to exercise [89,90]. In the first study, elastic compression stockings were worn either during both exhaustive exercise and recovery, or during exercise but not during recovery [89]. When the stockings were worn during exercise and recovery the post-exercise blood lactate levels were lower than a no-stocking condition, but when the stockings were worn only during exercise and removed during recovery post-exercise blood lactate levels were significantly higher. This was attributed to the compression stockings acting as a tourniquet to retain lactate within the muscular bed, a potentially deleterious effect that would not improve performance. Whether elastic (Lycra) sport tights caused a similar effect to that of compression stockings was also investigated [90]. In counterbalanced order, 8 healthy males ran on a treadmill at 110% VO2max. until exhaustion either wearing elastic tights during exercise and recovery, wearing tights during exercise

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only, or not wearing tights at all [90]. Unfortunately, no direct measures of performance were obtained since the run time to exhaustion in the first treadmill run was subsequently matched in the second and third trials. The design of this experiment was thus optimised to compare blood lactate response to identical exercise sessions, but not to determine whether tights provided any ergogenic advantage during high-intensity exercise. No significant differences in blood lactate concentration, heart rates or oxygen consumption post-exercise were observed among any of the conditions, and it would appear then that elastic (Lycra) tights provide neither ergogenic or deleterious effects on high-intensity exercise performance. The difference in physiological response between compression stockings and tights is likely to be due to differences in compressive properties between the products but no measures of these properties were reported. For elastic compression to increase venous return, the garment pressures need to be graduated along the limb and provide a minimum of 18 mm Hg pressure at the ankle and 8 mm Hg at the mid-thigh [87]. Compressive garments are also commonly worn by athletes participating in high-intensity power events and the influence of compression on these types of performance has been the subject of several investigations. One of the claimed effects of a support (compressive) athletic girdle is to act as a muscle conditioner, keeping muscles warm and minimising fatigue. The thermal effect of these garments during exercise is probably overstated, but no research quantifying muscle temperature effects of these garments has been identified. Low levels of compression have been hypothesised as enhancing perception of movement and performance under conditions of fatigue [91]. Although the highest jump in a round of standardised jump tests was not significantly affected, the mean force and power production over 10 jumps were higher when compressive shorts were worn [91]. Improved proprioception through wrapping the knees with elastic bandages has been demonstrated [92]. as have elastic sleeves [93], probably as a result of potentiated sensory feedback from skin or joint receptors. Knee wrapping commonly used by power lifters has also been effective in increasing force produced at the feet and enhance weightlifting performance [94]. The athletic performances of 6 males were compared when they wore on separate occasions a girdle then available on the market, and a prototype, results being compared with those obtained under a control condition (without a girdle). Eighteen 20-min exercise sessions on a vertical climbing machine were conducted (using a repeated measures Latin square design) [95]. Although high skin temperatures were maintained in exercise and cooling down when a girdle was worn, differences in athletic performance among the various treatments were not significant [95]. In a similar study, effects of use of compression garments (shorts and tights made from three medium-weight elastomeric blended fabrics (210.2–281.4 g/m2) were compared with non-use in terms of vertical jump performance following different fatigue tasks (endurance, strength, power), sense of hip joint position (proprioception), and muscle movement velocity on landing impact [96]. Forty college-aged athletic and non-athletic males and females (four groups of 10 in each category) participated. The compressive garment had no effect on the maximal power of the highest jump, but did enhance mean power output in the jump test both before and after the different fatigue tasks [96]. Joint position (hip) sense was significantly enhanced, and vertical velocity of muscle movement on landing significantly reduced with wearing the compression garment [96]. A possible psychological effect on wearing the compression garment was recognised [96]. Increasing resistance to body movement through particular clothing designs such as incorporating some form of stirrup and/or compressive material to develop and tone

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muscles was the underlying design principle of several patents taken out in the U.S.A. (e.g. [97] and [98]), for a resistive suit with stirrups, the latter with an outer loose-fitting sweatshirt; [99] covering restrictive exercise pants and hand stirrups). Whether any of the claims made for these products have been substantiated is not clear (e.g. ‘Motion of the leg requires greater muscular effort and serves to tone and develop the muscles of the leg’. . . : :‘develops the wearer’s muscles as the wearer engages in aerobic exercise’, [97]; and ‘not only stimulating cardiac response and general circulation but also developing the muscles along the length of the legs’ [99].

3.3 Layering Garment assemblies are usually composed of several items that are worn as layers one over another. Individual garments may be constructed from more than one layer of material (such as an outer shell and a lining). Additionally, some materials consist of two or more layers held together in some way: constructed as a double layer during the material fabrication operation (e.g. integrated double-layered fabrics or as separate layers joined by a separate machining operation or by one of several forms of adhesion or fusing). Thus, the effects that multiple layers of materials and garments have on the properties of garments, and hence on human performance, are complex. Several aspects need to be considered including effects on: (i) maintenance of human thermoneutrality (ii) body movement (iii) protective performance of garments, and biological effects.

3.3.1 Effects of Layering Materials and Garments on Maintenance of Human Thermoneutrality The effect of layering materials and garments on maintenance of human thermoneutrality is not yet fully understood because the effects of air spaces between the layers, and between the human body and the first layer on thermal resistance of the assembly itself are not fully understood. Still air layers increase thermal resistance, but openings in garments or bedding may result in a reduction in thermal resistance because warm microclimate air may be exchanged with cooler ambient air. Air spaces vary in width at different parts of the clothed body or the body beneath bed covers. Thus, the thermal resistance of any assembly is not simply an addition of the separate resistances of its’ constituent layers. Three studies are of particular interest: first, an examination of bedding used in covering infants, the thermal resistance of the bedding and how this changes with each of three physical arrangements simulating use, and the possible implications experiencing difficulty in maintaining thermoneutrality [100,101]; and second, two studies of the thermal resistance of multiple layers of garment materials in providing possible protection against an external heat source such as molten metal [102], or flame [103]. The size of air spaces between layers of bedding as they are arranged in use varied across the bedding and along its’ length (from 10 to 180 mm), and according to the number and selected properties of the constituent layers, i.e. 32 mm with a sheet and 107.5 mm with a sheet, two blankets and a duvet directly over the body; 62.8 and 144.2 mm for the same items but measured at a different part of the assembly [100]. The model of infant thermoregulation was being refined to include these observations on bedding at the time of writing (Wilson, personal communication). In the second case, layering as a means of increasing thermal

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protection against molten metal has been shown to be effective over a range of fabrics in the laboratory on material specimens [102], the greatest effect being from the thickness of the outer material layer, and although the material combination was claimed to be ‘still comfortable enough for 8 h use’ [102] evidence supporting this claim was not provided. The thermal resistance of a reinforced (layered) knee area of fire fighters’ garments increased over the non-reinforced version, but previous exposure history and whether the specimen was wet or dry also had a significant effect [103]. Again, human trials were not included. (See Section 5.)

3.3.2 Effects of Layering on Body Movement No investigations of layering effects on body movement, with all other variables constant, have been identified. Clearly, an effect on body movement would be expected. 3.3.3 Effects of Layering on Protective Performance of Garments, and Biological Effects on the Wearer Human performance can be impaired following absorption of chemicals to the body with effects such as headaches, nausea, diarrhoea. Biological indicators (such as the active ingredient of the chemical detectable in urine excreted by humans exposed to the chemical) have been used to determine the effectiveness of chemical protective garments and garment assemblies. Multiple layering of protective materials is considered to enhance protection against external hazards such as chemicals provided by the clothing assembly. In several studies only the materials, layered in the order in which they would be used and using conventional laboratory methods have been examined (e.g. [104,105]). An outer layer of carboxymethylated-treated cotton fabric held more of the pesticide methyl parathion irrespective of the underlayer being untreated, mercerised, or carboxymethylated-treated [106]. What effects air layers have in delaying breakthrough time or permeation rate seems unclear. In other studies, biological evidence of chemicals absorbed dermally by wearers of different types of garment assemblies has been identified. For example, differences between wearing clothing regularly worn in the lawn care industry in the U.S.A. (such as singlelayered cotton or cotton/polyester drill overalls, or trousers and short-sleeved knit polo shirts), and that designed and manufactured specifically for the purpose have been identified [107]. Certain body/garment sites are typically heavily deposited with chemical, particularly the lower portion of the body, and the front and back of the lower legs. The trousers were lined with a microporous film laminate between the knee and the lower hem front and back and in the abdominal area. The shirt had a yoke overlay of heavy cotton/polyester twill woven fabric and underarm gussets in an extensible mesh fabric. The fabric used for both trousers and shirt was 50%/50% polyester/cotton work-weight twill, selected to achieve an appearance of regular work wear. The balance of the shirt was 50%/50% polyester/cotton knit fabric. Crew-neck style 100% cotton undershirts were also worn, along with normal accessories. Significantly less (greater than 30%) 3, 5, 6-TCP was excreted when participants (n=6 adult males) wore the prototype protective gear than when they wore their company’s regular clothing each for two work days), and when the estimated area sprayed was taken into account, the difference between the garments was about 37% [107]. Results for individuals varied considerably. (Chlorpyrifoso, 0-diethyl-0-[3,5,6-trichloro-2-pyridyl] phosphorothioate was the active ingredient in the insecticide being used, and an earlier study [108] had shown chlorpyrifos was excreted in the urine as 3,5,6-TCP with no unchanged chlorpyrifos.) Layering has been used also to enhance the durability of garments worn under heavy conditions and to protect other items of clothing (e.g. those worn in the semiconductor

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industry [109]). Whether the probable increase in stiffness of the garments or parts of these adversely affected the wearer’s body movements and/or thermoneutrality is not clear. In the case of garments worn in the semi-conductor industry, the outer garment (a fullyencapsulated Saran-coated Tyvek suit) provided protection against chemicals and possible abrasion of the underlayer (a layer also protective against chemicals), and although possible heat exhaustion of the wearer of these double assemblies was acknowledged [109], no data from any observations on this effect were provided. Information on changes in skin and/or core temperature, and on ease of movement would have been useful.

3.4 Surface Area Covered The surface area of the body or part of the body which is covered by a garment is a basic aspect of design. It affects the thermal condition of the wearer through its effects on human thermoregulatory responses (See Section 5), as well as affecting the range of joint movement possible (particularly action of the foot and ankle with consequential effects on rear foot movement). 3.4.1 Coverage of the Lower Torso and Limbs The extent of garment coverage over the legs of 9 females exposed to very cool conditions (58C for 120 min; 60 min seated and 60 min light stepping exercises) had several physiological effects [110]. A significantly lower rectal temperature was evident when wearing shorts than when wearing long trousers during exercise; and the mean skin temperature was also significantly lower with shorts than with trousers [110]. Surface electromyography data from three muscles (biceps femoris, gastrocnemious, and tibialis anterior) suggested that exposing bare legs to a cool environment enhanced the motor unit activity over that with covered legs [110]. Acclimatisation to increasing heat during a 3-month period (spring to early summer) was affected by wearing a skirt or trousers, that is, different surface area coverage [111]. Tolerance to 378C and 30% rh was determined prior to and following the acclimatisation process using indicators such as rectal and skin temperature, and loss of body mass with sweating. The skirt-wearing group had a higher resting rectal temperature but lost less body mass and exhibited a lower increment in rectal temperature than the trouser group, showing improved heat tolerance with the season [111]. Why this would occur is unclear as one might expect that wearing trousers would keep the body temperatures higher than wearing a skirt. This study demonstrated the complex and often paradoxical interactions among clothing, the body, and the environment. 3.4.2 Coverage of the Foot and/or Ankle The effects of shoe design on human performance, particularly shoes for sporting activities and rehabilitation, have been examined in a number of investigations during the 30-year period 1970–2000. They can be grouped roughly in the following categories: with and without shoes; area of the foot and ankle covered; presence of additional support in the foot covering design; gross style differences; therapeutic devices. 3.4.2.1 Without and With Shoes Wearing shoes affects some aspects of walking, balance and running. For example, although there was little difference in the peak pressure and temporal parameters of foot function of a sample of males (n=21) and females (n=11) when walking bare-footed or with shoes, differences between walking bare-footed and shod were significant [112]. The main effect of shoes appeared to be in modifying the performance of the fore-foot by altering the pressure

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distribution across the metatarsal heads and thereby increasing the contact time for the toes [112]. In another study gluteal muscles (maximus and medius) were significantly more active when participants (n=15 healthy adults, 5 men, 10 women) wore ‘balance shoes’ while walking than when they walked bare-footed, the difference being attributed to stimulation of the proprioceptive mechanism in walking (since the sole of the balance shoe provided an unstable base of support) [113]. Wearing running shoes has been shown to affect angular displacement of the foot relative to the horizontal or vertical [114]. Fifteen participants ran in each of three conditions (barefooted, with shoes without windows, and with shoes with windows), were filmed from behind, and in analysing the film, the heel was found to move similarly but not identically to the heel counter [114]. The maximum change of pronation was bare-footed 13.7  3.78; shoes with windows 14.1  3.88 for the shoe and 12.1  3.78 for the heel inside the shoe; shoes without windows 14.9  4.28 shoe [114]. That is, pronation in running was reduced by wearing the running shoe. Footwear separates the plantar surface of the foot with its’ tactile sensitivity from the ground surface, and reduces awareness of foot position. Plantar tactile sensitivity and awareness of foot position are to some extent age-dependent (e.g. over 65 þ years [115] and athletic footwear worn by older males impaired their stability in walking. Whether also footwear-dependent, has been investigated observing the performance of younger men (n=17, mean age 33 years) walking on a balance beam while bare-footed and that when they wore various pairs of athletic shoes (differing in hardness and thickness of the mid-sole only) [116]. Better stability of the participants was observed with the harder mid-sole, and a thinner mid-sole [116], a result similar to that obtained from the older participants. This issue of reduced plantar sensitivity has also been linked to use of footwear designed specifically to enhance plantar comfort when walking [117], and has stimulated considerable debate and confusion (e.g. [117–121]). Not surprisingly, the popular literature of the time reflected this confusion (e.g. [122]; Tennis, 1988 #588). One effect of wearing athletic footwear which typically exhibits plantar comfort when walking, running or jumping is that the perceived impact is reportedly less than the actual impact and this reportedly results in inadequate impact-moderating behaviour (and possible consequential injury) [117]. The feasibility of a footwear safety standard in which this illusion was eliminated was investigated during the early 1990s [117] although such a standard seems not to have proceeded. Twenty participants gave numerical estimates of plantar discomfort produced by simulated locomotion, with the foot supported by either a smooth rigid surface or a rigid surface with 2 mm high rigid irregularities. Discomfort was perceived only when vertical and horizontal loads were applied simultaneously, but from loads as low as 0.4 kg/cm2 [117]. Dexterity of digits is not restricted to those of the hand, and a number of patented items have been designed to retain dexterity of the toes such as with foot gloves (e.g. [123]). Objective measurement of changed performance in dexterity of the toes has not been identified.

3.4.2.2 Area of the Foot and Ankle Covered The area of the foot and ankle covered by footwear may affect performance. For example, shoe height (whether low or a 3/4 top basketball shoe) was shown to not affect the ability of participants (n=20) to resist an eversion moment at any angle of ankle plantar flexion over the range 08, 168, 328 [124]. However, resistance to inversion was higher when the 3/4 top basketball shoe was worn at 08 and 168 ankle plantar flexion by 29.4 and 20.4%, respectively

Clothing, Textiles, and Human Performance

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[124]. Thus the height of an athletic shoe (area coverage) can increase resistance to an inversion moment in moderate ankle plantar flexion and therefore be expected to provide some protection against ankle injuries.

3.4.2.3 Presence of Additional Support Provision of support in footwear designed for sport is considered one way of reducing excessive load placed on the body and, based on a review of papers on anatomical, orthopaedic, and epidemiological issues, can be achieved by altering the shoe design [125]. Performance in a vertical jump test and an obstacle course running test, along with ankle kinematics on landing, was the basis of the comparison of two prototype shoes with identical soles and mid soles, differing only in the design of the uppers [126]. The upper designed to provide greater support, had a high top, heel counters, and rear-foot lacing; the other had a low top and no other feature for support (Fig. 3.2a). (The weight of the shoes would have differed because of the different quantities of constituent materials although the authors do not suggest this. Neither the weight of either shoe type nor the materials used in

Fig. 3.2

Design of sports shoes for enhanced performance (a) Variation in uppers for movement control (Brizuela et al., 1997) (b) Strength shoeTM for muscle conditioning (Cook et al., 1993)

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the uppers were reported.) In the shock attenuation test (n=5 males), use of the highsupport shoe resulted in higher fore-foot impact forces and higher transmission to the head, but lower shock transmission to the tibia [126]. Smaller ranges of eversion but larger ranges of inversion at the ankle on landing were observed with these high-support shoes. In the performance tests (running and jumping, n=8 males) the high-support shoe reduced the height jumped by 3% ( p