Fashion and function: challenges faced by textiles incorporated with phase change materials

Designers focus on fashion and appearance, whereas safety and protection engineers and physiologists emphasize functions in terms of developing functional and protective clothing. Phase change materials (PCMs) have been used in textiles and clothing to achieve cooling or warming function. The objective of this paper was to compare effectiveness of PCM cooling or warming determined by critical factors. Cooling or warming effectiveness and duration were directly dependent on physical activity level (body heat production), PCM mass and temperature gradient between the skin temperature and PCM phase change temperature. Given these factors, textiles and clothing incorporated with PCMs may be lightweight, well-designed, smart and fashionable, but are insufficiently functional when the amount of the PCM and latent heat are small relative to the body heat production and duration of activities. It is therefore challenging by incorporating PCMs into textiles and clothing to achieve desirable light weight, fashion, thermal comfort and effective alleviation of body heat strain unless the critical factors are taken into account

Effects of natural solar radiation on manikin heat exchange

The main objective was to compare short wave radiation from Thorn lamp to solar radiation. In sun all manikin front zones get more or less evenly radiated but in the lab the radiated power reaches some zones more than others. Tests were carried out on the thermal manikin Tore under clear sky in a building corner facing the sun. The manikin was turned so that in the end of each trial the sun faced manikin front. Basic tests without radiation were carried out in homogenous conditions in the climatic chamber. 4 sets of clothing were tested: black Nomex (BN), orange Nomex (ON), white cotton (WC) and reflective Nomex (RN). Helly-Hansen underwear (super stretch, polypropylene) was used under all coveralls. Thermocouples were fixed at chest on underwear inner and outer surfaces and outer layer inner and outer surfaces for textile surface temperature measurements. From basic tests there were estimated the heat losses for particular outdoor conditions. The insulation values were corrected for air velocity according to EN 342 (2004). The difference between the calculated heat losses and actual measured heat losses outdoors gave heat gain from sun for those particular conditions. There was a clear difference between BN and the other suits and RN and the other suits, however, ON and WC were quite similar. The highest textile temperatures were recorded for BN and lowest for RN. A difference between ON and WC was present, too. The curves followed the same pattern as observed from the manikin tests with solar lamps in the climatic chambers: underwear had often the highest temperatures

Thermal stress on firefighters in extreme heat exposure

Five students of a rescue training school cycled at 50 W for 20 minutes at 20 °C before walking up to 30 minutes in a climatic chamber at 55 °C and 30 % relative humidity. Four different types of clothing ensembles were used differing in terms of thickness and thermal insulation value were tested on separate days. All subjects completed 28-30 minutes in light clothing, but quitted after 20-27 minutes in three firefighter ensembles due to a rectal temperature of 39.0 °C or subjective fatigue. No difference in the evolution of mean skin or rectal temperature was seen for the three turnout ensembles. Sweat production amounted to about 1000 g in the turnout gears of which less than 20 % evaporated. It was concluded that the small differences between the turnout gears in terms of design, thickness and insulation value had no effect on the resulting physiological strain for the given experimental conditions

Effects of cooling on muscle function and duration of stance phase during gait

Introduction: Cold exposure alters muscular function. Muscle cooling influences the neuromuscular activation during maximal isometric voluntary contractions (MVC) and the amplitude of surface electromyography (sEMG) [1],[2]. It also slows down the mechanical process during contraction [3]. The purpose of this study was to investigate the effects of local cooling in cold water at 10 °C for 20 min in a climate chamber on lower leg muscle activity and gait pattern. Methods: Sixteen healthy adults (eight females), aged Mean (SD) 27.0(2.9) years; body mass 66.3(9.8) kg; and height 169.5(7.8) cm participated in this experimental study. The median frequency (MF) and mean power frequency (MPF) of sEMG from tibialis anterior (TA) and gastrocnemius medialis (GM) muscles during MVC in ankle planter (PF) and dorsi-flexion (DF) against a hand-held dynamometer as well as contact times on a force plate during gait before and after cooling were measured and analysed. Results: The MF and MPF were significantly lower (P<0.01*) in both TA and GM muscle during MVC and in TA during gait trials after cooling. However, the frequency analysis for GM muscle showed no significant difference (P=0.46 and 0.06, respectively) either in MF or MPF during walking on level surface (table 1). Table 1: The means and SD (Hz) for the MF and MPF of the TA and GM during gait and MVC trials before and after cooling (N=16). sEMG Tibialis Anterior (TA) Gastrocnemius Medialis GM Pre Cooling Post Cooling Pre Cooling Post Cooling Gait MF 83.0±10.2* 69.9±9.6* 81.6±12.6 79.3±11.1 Gait MPF 99.7±11.5* 82.3±11.7* 99.8±13.2 93.2±12.4 MVC MF 87.0±9.7* 50.0±6.1* 111.7±16.7* 90.8±14.8* MVC MPF 100.7±10.6* 59.8±7.7* 129.1±15.3* 101.0±16.1* Fig 1: Duration of stance phase in gait trials. Additionally, the post cooling stance phase over the force plate was significantly (P= 0.013) longer than pre-cooling. Discussion: The significant time difference might be caused by the cold induced MF and MPF decrease in sEMG. Our previous investigation reported that cooling increased the sEMG amplitude and produced fatigue like responses in the leg muscles [2]. Moreover, other studies showed that muscle fatigue resulted in electromechanical delay during cold exposure [1], [4]. Conclusion: Moderate degree and duration of cooling may affect muscle motor unit firing rates, thus shifting the sEMG spectrum to lower frequencies, therefore decreasing the leg muscle force production. The result suggests that muscle cooling can cause cold induced frequency decrease in sEMG similar to fatigue response and lead to reduced muscle performance. References: 1. Cè, E., Rampichini, S., Agnello, L., Limonta, E., Veicsteinas, A., & Esposito, F. (2013). Effects of temperature and fatigue on the electromechanical delay components. Muscle & Nerve, 47(4), 566-576. doi:10.1002/mus.23627. 2. Halder A, Gao C, Miller M. (2014). Effects of cooling on ankle muscle maximum performances, gait ground reaction forces and electromyography. Journal of Sports Medicine.doi:10.1155/2014/520124. 3. Drinkwater, E. (2008). Effects of peripheral cooling on characteristics of local muscle. Medicine and Sport Science, 5374-88. doi:10.1159/000151551. 4. Rampichini, S., Cè, E., Limonta, E., & Esposito, F. (2014). Effects of fatigue on the electromechanical delay components in gastrocnemius medialis muscle. European Journal of Applied Physiology, 114(3), 639-651. doi:10.1007/s00421-013-2790-9

Thermoregulatory manikins are desirable for evaluations of intelligent clothing and smart textiles

Thermal manikins have been used to measure thermal properties of clothing. The use of thermal manikins has made a step forward in terms of quantifying thermal properties of clothing in a 3-D manner compared with the use of hotplates for material testing. The effects of clothing properties measured on the thermal manikins under steady state (constant manikin surface temperature and constant environmental condition) have usually to be validated by human subject tests. The thermal insulation and evaporative resistance values measured in the constant conditions are also used in modeling to calculate heat balance, predict human thermal physiological responses, and thermal comfort. However, in many real life situations, clothing properties (e.g. moisture transfer), in particular the clothing properties with smart materials, e.g. phase change materials (PCMs), environmental conditions, sweating rate, skin temperatures are neither constant nor uniform. These make mathematical modeling complicated to take into account various transient, non-uniform conditions, and changeable properties of smart clothing which is becoming increasingly popular (Tang and Stylios 2006). Moreover, skin and core temperatures rather than heat loss or storage are commonly used to evaluate thermal comfort, define hypothermia and hyperthermia and evaluate heat strain. Therefore, the direct prediction of thermophysiological responses (skin and core temperatures) based on manikin measurements are valid (Psikuta and Rossi 2009), and could be considered another step forward towards direct evaluation of human-clothing-thermal environment interactions. In the case of measuring a personal cooling system, current standard specifies the measurement of the average heat removal rate from a sweating heated manikin (ASTM F2371-10). This heat removal rate is not constant for the PCMs. The objective of this study was to investigate the gap between the measured heat removal rate of smart clothing with PCMs obtained on a thermal manikin in a stable state, and clothing effects on local human skin and on core temperature, to compare the difference of the results obtained from both methods, and to highlight the need for developing intelligent thermoregulatory manikins

Effects of Cooling on Ankle Muscle Strength, Electromyography, and Gait Ground Reaction Forces

The effects of cooling on neuromuscular function and performance during gait are not fully examined. The purpose of this study was to investigate the effects of local cooling for 20 min in cold water at 10 C in a climate chamber also at 10 C on maximal isometric force and electromyographic (EMG) activity of the lower leg muscles. Gait ground reaction forces (GRFs) were also assessed. Sixteen healthy university students participated in the within subject design experimental study. Isometric forces of the tibialis anterior (TA) and the gastrocnemius medialis (GM) were measured using a handheld dynamometer and the EMG was recorded using surface electrodes. Ground reaction forces during gait and the required coefficient of friction (RCOF) were recorded using a force plate. There was a significantly reduced isometric maximum force in the TA muscle