A Review of Contemporary Techniques for Measuring Ergonomic Wear Comfort of Protective and Sport Clothing

2.1 Ergonomic wear comfort

Ergonomic comfort of clothing is most important for sportswear and personal PC to support the wearer during different activities. The most important requirements for ergonomic wear comfort that the textile should possess are allowing freedom of movement, reducing load/strain, and maintaining the body shape [31, 32]. These are predominantly characterized by the garment’s fit design and pattern construction and can be influenced by the elasticity or the stretchability of the material [33]. Ergonomic considerations dictate that the mechanical characteristics of clothing match the motion, degree of freedom, range of motion (ROM) and force, and the moment of human joints. The shape and fit of the garment vis-à-vis the human body, as well as the pressure and friction exerted by the garment on the body, are some of the factors that affect this aspect [34].

One of the basic functional requirements for all types of sportswear is the wear comfort, which is the global comfort during wearing; it includes thermal properties, passive touch (or fabric touch [to the skin], and not hand of textile) and ergonomic comfort. Wear comfort is important for players as it may enhance performance by providing suitable physiological conditions in all climatic extremities [35]. Concerning ergonomic wear comfort, in active sports such as running, skin extension and contraction take place due to the high degree of body movement, which alters the corresponding body measurements [36, 37]. Sportswear clothing should not restrain these movements; else, discomfort will be created due to undesired garment pressure. Body fabric is commonly used in tight-fit running shorts, which provide the desired shape and size with adequate room for body movements [38, 39, 40, 41].

2.2 Why ergonomic wear comfort?

Providing comfort in clothing for the moving body is a complex task. Interactions among body sizes and shapes, physiological variations, material properties, design choices, environmental challenges, and activities are exponential in their number. The impact of clothing on the comfort and performance of individuals at work or sport is of particular importance. Industrial and sport PC is governed by protection requirements, and sport clothing is generally selected on the basis of performance and comfort [42]. The impact of PC on performance is determined by the nature of the work or sport, the metabolic rate required, the ambient environment, and the characteristics of the PC [43]. The ergonomic requirements and ergonomic aspects according to the degree of importance for industrial PC users are as follows: (1) proper fit or sizing; (2) reduction of hotness and improving ventilation through pattern, design and material selection; (3) reduction of weight and reduction in obstruction to work; and (4) ease of mobility [44].

Ergonomics and sports science are closely tied together when taking human performance into consideration. Both workers and athletes have to optimize the level of their performance in relation to the external demands [45]. There are many industrial situations where workers are required to wear personal PC and equipment (PPE), e.g., firefighters, chemical workers, cold-store workers, army personnel and those working in the steel and forestry industries. Although this PC may provide protection from the primary hazard, e.g., heat or chemicals, it can also create ergonomic problems [46, 47, 48]. In recent years, many PPE product standards have been introduced. These have helped to improve the quality of the PC and thus have increased the safety of the workers. There are important side effects to PC, and typically with increasing protection requirements, the ergonomic problems typically increase. Often, the main problem is the added load on the body in terms of weight. Moreover, reduced mobility due to garment stiffness reduces the freedom of movement and may increase the risk of falls or getting caught in machinery. As a result, the PPE may actually reduce safety rather than improving it, especially after the PPE has been worn for a certain duration. As a consequence, the user may refrain from wearing the necessary protection.

For instance, when performing a task in a fire, the heat and perspiration generated from the body become trapped inside the PC. The heat and moisture thus generated result in heat stress and physical fatigue of the firefighter, which hinders their work. Therefore, the clothing design and material layers for firefighter suits must be chosen carefully to balance protection and comfort, with emphasis on choosing the lightest and the most breathable system that provides acceptable thermal insulation [43, 49]. Therefore, reduced thickness, lower weight and lower stiffness should positively affect comfort, thermal resistance, evaporative resistance and total heat loss; however, insulation from heat and fires must remain high and runs counter to the methods used to improve comfort while working. An open structure of the fabric may lower evaporative resistance and increase total heat loss through evaporative cooling [50, 51]. Considering the physical movement of humans, many manufacturers are convinced of the need to include vents in some of their outdoor athletic apparel to address thermal burden and/or moisture issues [52].

2.3 Attributes for sportswear and PC

i. Allowing freedom of movement/improving body movement: This enables ergonomic wear comfort to improve due to the garment’s pattern, fitness, and the stretchiness; lower weight, reduced thickness and less stiffness; and recovery of the materials. These factors play a significant role in affecting the body movement. Especially, elastic textiles can improve the ease of movement of clothing and, thus, the ergonomic wear comfort [53, 54]. In sport activities, there is a dynamic interaction between the garment and the body: this includes thermophysiological, tactile, and psychological interaction. These are all dependent on various properties of the fabric and garment, as well as on environmental conditions and the type and level of activity of the wearer [55, 56, 57]. Today’s stretchable garments for sports and outdoor wear play an important role in optimizing an athlete’s performance by providing freedom of movement, maximizing comfort, minimizing the risk of injury or muscle fatigue, and reducing friction or drag [58, 59]. A well-fitted sport garment must not interfere with, impede, or restrict the body movement relative to the end use. For instance, it is impossible to perform any exercise while the garment restricts body movements. On the contrary, the garment must enable the free exercising of the sport activity and the performance of the ROM expected of him or her.

ii. Reducing load/strain: Stress, training, fatigue, load, and environmental conditions have an influence on the evaluation of human performance and the degree of freedom. Uneven weight distribution of the garment and heavy loads can create discomfort and an irregular strain on the musculoskeletal system, in addition to reducing the ergonomics of a gesture [60, 61]. It is true that functional and protective fabrics are superior in their hand properties (feel, stiffness, drape, and bulk) [62, 63, 64]. The aim should be to provide a lighter garment with a better-tailored and comfortable fit, as this would contribute to higher garment functionality and improved ergonomics. At the same time, a lighter fabric would allow some moderate gains in reducing the heat load. For military PC, the research and development process has developed several new protective material systems and incorporated design features into a uniform concept targeted specifically at the reduction of thermal burden when the individual protective equipment is worn. Reducing thickness, minimizing weight, and lowering stiffness should positively affect comfort, thermal resistance, evaporative resistance, and total heat loss.

iii. Maintaining the body shape: Ergonomic clothing relates for the most part to wearing attire, especially to apparel developed to suit the curvature and the movement and development of the human body. This enables increase in user comfort, as the article of clothing is highly wearable. The making of clothing to which aesthetically appreciable curvature is applied inspires people to buy the product [15, 65, 66, 67].

iv. Mechanical properties: Mechanical properties of the fabric can be important determinants of comfort and ergonomics in PC [68, 69]. Mechanical properties such as tactile stiffness of the material components contribute to the flexibility and comfort of PC designed for emergency responders.

v. Breathability: Moisture management property is an important aspect of any fabric meant for active sportswear and PC, which decides the comfort level of that fabric. Every human being sweats during different kinds of activities. An important feature of any fabric is how it transports this water out of the body, so as to make the wearer feel comfortable [70, 71].

3.1 Measurement of freedom of movement

Human performance can most certainly be impaired by apparel with poor fit, restricting factors such as ROM, reach, and manual dexterity. The ergonomic principles of optimizing fit; reducing weight of the garments or garment assembly; and altering the physical stress of performing a task through innovative garment design remain central to optimizing human performance. However, the garment has to fit the wearer without restricting the full ROM. It needs to be comfortable and aim not to abrade the skin. Ergonomic considerations dictate that the mechanical characteristics of clothing match the motion, degree of freedom and ROM, as well as the force and moment of human joints.

Fit testing of clothing prototypes on human fit models is common practice in the apparel industry to refine patterns before clothing is manufactured [73, 74, 75]. Fit models sit, walk, and, in the case of active wear, test the prototype by engaging in the sport for which it is designed. In the research community, both controlled fit studies and wear tests that challenge the garments with actual working conditions are common practice in the design and testing of functional apparel. Studies using instrumented mannequins are also common.

Development of robotic testing devices that duplicate the joint motion and ROM of a human, with the movements internally inducted, could result in a reliable laboratory-based test of clothing ensemble performance for the required ROM [76]. ROM is an important performance measure for workers wearing personal PC. It is frequently used to compare competing garment designs and to assess worker mobility [77]. Motion studies evaluate the wearer’s ability to perform repetitive movements and typically measure ROM or reach capability.

A range of experimental models have been used to objectively assess mobility restriction caused by PC. Initially, a test battery of simple movements and measurements, which could be performed with minimal training and equipment, was developed [78]. More recent studies have measured encumbrance using goniometers, Leighton flexometer, a potentiometer-driven microcomputer system [79, 80], and inclinometer [81].

Among the measures of mobility restriction, ROM has two obvious advantages. First, ROM can be objectively quantified in terms of joint angles or reach distances. Reach distances often involve more complex motions, with movement occurring in multiple planes and involving multiple joints, whereas joint angle measurement is well suited for use in the laboratory. A second advantage of using ROM measurements is that they can be taken with instruments that are relatively unsophisticated and easy to use. The ease of motion can be assessed through wearer trials by performing a series of practical activities based on the wearer’s body movement [82]. Figure 2 shows the distribution of electro-goniometers on the body of the subjects.

Figure 2

Distribution of electrogoniometers on the body of the subjects (copied from Ciesielska-wróbel et al. [83]).

Figure 3

Distribution of the electrogoniometers on the body of the subjects (copied from Ciesielska-wróbel et al. [83]).

Figure 4

Subjective rating scales for subjective sensations (copied from Wu et al. [109]).

Figure 5

Making measurements: connect the sensor to PicoPress (copied from Electronica [125]).

The effects of different garments or garment assemblies on the ROM have been studied using a variety of goniometers and flexometers, none of which require calibration, installation or set-up. Dorman and Havenith [56, 57] showed the effect of PC on mobility, and Huck tested different designs of firefighter turnout gear [85]. The electrogoniometer system uses strain gages mounted within a protective spring. End blocks are attached to the subject’s skin. The strain gages in the blocks are connected to the data logger, and thus, the information about the movement is collected [83].

3.2 Influence of the ergonomic wear comfort on the thermal wear comfort

Changes to improve the ergonomic wear comfort may influence the thermal comfort, which requires measurement of the thermal properties to verify whether they are negatively influenced or not [86]. This can be achieved through human testing of the ensembles or manikin testing. For certain PPEs such as those for firefighters, the ergonomic wear comfort is also closely linked to the thermal comfort in the sense that ergonomic changes are done to improve the heat balance in the protective suit.

The thermal wear comfort of the textile material is dependent on moisture regain, porosity, density and air permeability characteristics of the fabric. These characteristics also have an effect on the ergonomic wear comfort property of the fabric. The fabric weight increases as the amount of fibers in the fabric increases per unit area, which will reduce the amount of air transport in the fabric. This is directly related to the amount of air entrapped in the fabric. In this case, the thermal property of the fabric will have higher conductivity than the entrapped air [87]. Therefore, we can conclude that the fabric structure of textile materials has an effect on moisture regain, porosity, density, and air permeability property, and this will have an effect on the thermal and the ergonomic wear comfort property of textiles.

Evaporative resistance and thermal insulation of clothing can be measured directly in humans. For example, Taylor et al. [88] developed a method to determine the effective evaporative resistance of clothing in vivo and concluded that the method, in combination with partition calorimetry, can determine the resistances of clothing with dry and wet heat loss for both resting and working subjects [89]. The evaporative resistance from the evaporative heat loss and vapor pressure at the skin surface and in the environment is estimated and used to compare the evaporative cooling capacity of PC ensembles [90].

In order to accurately determine the evaporative resistance and thermal insulation of clothing, thermal manikins have been developed since the 1940s [91, 92]. In terms of development, thermal manikins can be grouped into four types [93, 94]. The first is the standing (viz., nonwalking) and nonperspiring type [95, 96]. The second is the movable (viz., walking), but nonperspiring type, such as the copper manikin “Charlie” in Germany [97]. The third type is the nonsweating manikin, but sweating is simulated by wetted skin. This type of manikin is currently used by Holmer in Sweden, McCullough in the USA, and Havenith in Britain. The fourth type is the perspiring forms of types 1 and 2, which adds a lot of complexity, such as “Taro” in Japan [98], “Kem” in Japan [99], “Coppelius” in Finland [100], “Sam” in Switzerland, and “Walter” in Hong Kong [101].

Thermal manikin systems are perfect for a broad range of clothing and environmental testing. The degree of thermal comfort depends greatly on the local environment [102]. Human beings usually use different types of clothing and respond differently to heat transfer from different body areas. The various types and amounts of clothing that manikins use today make comparative interpretation of results from different manikins/methods very complicated. In order to facilitate comparison of results, the methods should be independent both of the manikin used and the clothing worn. The total heat transmitted through clothing is commonly considered the sum of the dry heat transfer and the evaporative heat transfer, and it is measured under nonperspiring conditions, e.g., a dry thermal manikin is frequently used to calculate the dry heat transfer when the body is perspiring or even sweating heavily [102, 103, 104]. There is also a possibility of error in the measurement of water vapor resistance. In order to ascertain how perspiration or sweating affects the clothing thermal insulation during dry heat transfer, a novel perspiring fabric thermal manikin is used to measure the clothing thermal insulation in cases of both little perspiration and more perspiration.

3.3 Fabric physical measurement through wearer trials

Modern textile products make their most valuable contribution to the well-being of humankind, but their acceptability depends upon the permitting of thermal comfort and a satisfactory “feel” in the area of fabric–skin contact. The main purpose of the wearer trial is to gather information from the respondent at the garment level [105, 106, 107]. The principle of the user performance trial is to investigate clothing while in actual use, hence providing practical information. This will involve identifying a sample of users of the clothing and observing the properties over a period of time representing realistic conditions. Questionnaire techniques and possibly some physiological measures can be used [108, 109]. Therefore, wearer trial is an important technique for clothing comfort research, although the process tends to be expensive and time consuming and the results tend to be less reproducible and consistent. This method has been used for evaluating moisture, as well as the ergonomic, thermal, tactile, and esthetic comfort. Wearer trials can also be designed to obtain some objective sensory measurements under different wearing conditions that are relevant to the behavior of the knitted underwear [110]. During the test, subjects are asked to wear the garments under study; then, each subject has to rate the garment on selected comfort sensation. Various sensory descriptors are generated from the responses of the respondents, and the testing conditions are selected to maximize the perceptions of various sensations. Attitude scales are designed to obtain various sensory responses for a particular item/garment.

According to predetermined protocols, wearer trials are conducted under controlled testing conditions, and the data is collected and analyzed. The analysis of the firsthand physiological data gathered from wearer trials can provide insight into the ergonomic design of clothing.

3.4 Measurements of physiological parameters in human wear textiles in the context of Ergonomics

Different researchers have worked on direct sensing from the human body using different methods. This includes the hydrostatic pressure-balance method [111], pneumatic pressure sensors [112, 113, 114], resistive pressure sensors [115, 116], elastic optical fiber pressure sensors [117, 118], and capacitive pressure transducers [119]. Owing to the relative stability and accuracy, the most popularly used types of pressure sensing devices are the Air-pack sensor developed by AMI Techno Co., Ltd (Tokyo, Japan) [120] and the flexiforce pressure sensor developed by Tekscan, Inc. (Boston, MA, USA). However, insertion of the sensor between fabric and skin could bend the sensor and cause discrepancies in the measurements.

The “garment pressure” is one of the important features used to evaluate the performance in terms of comfort, function, and security of compression garment. Pressure from compression garment onto human body should be in an appropriate range.

Therefore, it is still important to build a scientific and precise evaluation system for pressure comfort. Compression was examined by Yongrong Wang et al. [61] using the Air-pack type contact pressure sensor (AMI Techno Co., Ltd) for sensory tests, and a novel stretchable compressive belt was designed and developed, which was used to control the pressure applied on separate body parts by the belt’s extension and contraction [121].

Flexiforce pressure sensor is constructed of two layers of polyester substrate; conductive silver is applied on each layer, followed by a layer of pressure-sensitive ink. Sensors respond to single-point force loads over a sensing area of 9.53 mm with claimed operating range 0-1 lb. This has found applications in many fields, especially suitable for medical applications for compression therapy: the application of persistent pressure on the surface of a limb, most often a leg, is a widely accepted clinical treatment for chronic venous disorders due to their thin and flexible construction and ability to operate at low pressures [122].

I-Scan™ pressure mapping sensor is a versatile pressure mapping system developed by Tekscan, Inc., which provides accurate measurements of both force and pressure between two surfaces. The Tekscan system is easy to use and very dependable and has helped to improve ergonomic advantages. The interface pressure data collected offers vital information and insight to enhance product design, manufacturing, quality, and research [123].

Venkatraman and Taylor [29, 124] investigated the pressure profile of compression garments for cyclist participants using Tekscan pressure sensors on various points (lower limb). Trial wear is required to investigate user perceptions for the fit, comfort, ease of wear, tactile sensation, and overall satisfaction. Hence, suitable inferences drawn from these findings enable the ascertainment of the performance of compression garments and aid in further development [124].

Accuracy and reproducibility of direct measurements from human subjects are difficult to achieve because the sensors are readily affected by noise due to body movement. On the other hand, Microlab Electronica have developed a portable digital gauge called PicoPress to be used to measure the pressure exerted by a bandage or garment for medical purposes. The instrument utilizes a circular transducer made out of an ultrathin biocompatible material in which a known quantity of air is inserted. The transducer is placed between the skin and clothing/bandage.

During sport activities, compressive textiles reduce wobbling masses, muscle vibration, and swelling, and even the skin is influenced by the pressure of the compression textile, as claimed by Sioson et al. [126]. New properties require new laboratory test methods to determine the function and its effect. However, sensorial comfort is difficult to predict as it involves different factors. Besides, ergonomic comfort, sometimes also called aesthetic comfort, can be tested with different objective methods. One of the traditional methods is to measure the space between the body and the clothing and then calculate the fitting index.

3.5 Pressure comfort measurement: numerical simulation of garment pressure

Modeling and simulation of textile fabrics represents an important field of scientific research. Interdisciplinary cooperation of scientists in the fields of physics, mechanics, mathematics, and informatics is necessary for the simulation and prediction of textile properties and behavior. Modeling tools are useful for estimation of skin sensorial comfort, and further research activities are required [127].

Researchers have developed a mathematical model of geometric nonlinearity based on the theory of contact mechanics to simulate the dynamic garment pressure distribution on a 3D human body during wear [128]. The model was able to illustrate the dynamic garment pressure distributions when a rigid female body wearing a set of perfect-fitting garments is in motion. The numerical computational results show that the model can predict, without the actual production of the garments, the dynamic mechanical behavior of garments during wear, including the garment deformation, the garment pressure, the internal stresses in the garment, and the effects of the garment‘s weight and inertia force on the dynamic wearing process [128, 129]. However, as the human body is assumed to be rigid, the dynamic mechanical interactions between the body and the garment cannot be simulated realistically, especially the deformation of the human body and the pressure distribution under the skin and soft tissues.

3.6 Subjective assessment coupled with objective measurement of pressure comfort

There are many works that combine both objective and subjective systems for measuring clothing comfort as it is believed that objective systems do not ensure a full representation of thermophysiological, sensory/tactile, and movement comfort due to their lack of a human element or their focus on a single property [130]. The objective methods provide quantified results, but in some cases, such quantified results are quite far from the real perception of HC [130, 131].

Clothing comfort is very subjective. Evaluation of pressure comfort must combine the predicted pressure and the sensation index from a large volume of experiments involving wear trials. It needs much work on psychological evaluation of garment pressure, from which a series of psychophysical models are developed based on the investigation of the relationship between objective stimuli and psychological perceptions and the investigation of the relationship between the predictions and the objective measurements. It is believed that subjective assessment is a complex synthesis of many kinds of psychological and physiological response of individuals. Consequently, the subjective responses of wearers are not only decided by the physical properties of garments but also by the wearing habits and experiences of wearers. Therefore, questionnaire design is critical for the rating of subjective sensations. Factor analysis is usually applied to clarify the effect of factors, such as different garment sizes and fabrics with different extensibilities. Regression analysis of clothing pressure, fabric extensibility, and garment fitness is used to establish the relationship between subjective assessment and objective physical factors [105, 132, 133].