The effect of two kinds of T-shirts on physiological and psychological thermal responses during exercise and recovery

The aim of this study was to investigate the physiological and psychological responses during and after high-intensity exercise in a warm and humid environment in subjects wearing shirts of different fabrics. Eight healthy men exercised on two separate occasions, in random order, wearing two types of long-sleeve T-shirt: one made of polyester (PES) and the other of cotton fabric (CT). They performed three 20 min exercise bouts, with 5 min rest between each, and then rested in a chair for 60 min to recover. The ambient temperature was 25 °C and relative humidity was 60%. The exercise comprised of treadmill running at 8 km/h at 1° grade. Rectal temperature, skin temperatures at eight sites, heart rate, T-shirt mass and ratings of thermal, clothing wettedness, and shivering/sweating sensation were measured before the experiment, during the 5 min rest period after each exercise bout, and during recovery. Nude body mass was measured before the experiment and during recovery. The physiological stress index showed that the exercise produced a state of very high heat stress. Compared with exercise wearing the CT shirt, exercise wearing the PES fabric produced a greater sweating efficiency and less clothing regain (i.e., less sweat retention), but thermophysiological and subjective sensations during the intermittent high-intensity exercise were similar for both fabrics. However, skin temperature returned to the pre-exercise level faster, and the thermal and rating of shivering/sweating sensation were lower after exercise in the warm and humid environment in subjects wearing PES than when wearing the more traditional CT fabric.     

The effect of two kinds of T-shirts on physiological and psychological thermal responses during exercise and recovery

The aim of this study was to investigate the physiological and psychological responses during and after high-intensity exercise in a warm and humid environment in subjects wearing shirts of different fabrics. Eight healthy men exercised on two separate occasions, in random order, wearing two types of long-sleeve T-shirt: one made of polyester (PES) and the other of cotton fabric (CT). They performed three 20 min exercise bouts, with 5 min rest between each, and then rested in a chair for 60 min to recover. The ambient temperature was 25 °C and relative humidity was 60%. The exercise comprised of treadmill running at 8 km/h at 1° grade. Rectal temperature, skin temperatures at eight sites, heart rate, T-shirt mass and ratings of thermal, clothing wettedness, and shivering/sweating sensation were measured before the experiment, during the 5 min rest period after each exercise bout, and during recovery. Nude body mass was measured before the experiment and during recovery. The physiological stress index showed that the exercise produced a state of very high heat stress. Compared with exercise wearing the CT shirt, exercise wearing the PES fabric produced a greater sweating efficiency and less clothing regain (i.e., less sweat retention), but thermophysiological and subjective sensations during the intermittent high-intensity exercise were similar for both fabrics. However, skin temperature returned to the pre-exercise level faster, and the thermal and rating of shivering/sweating sensation were lower after exercise in the warm and humid environment in subjects wearing PES than when wearing the more traditional CT fabric.     

Effects of caffeine and menthol on cognition and mood during simulated firefighting in the heat

This study examined the separate effects of caffeine and menthol on cognition and mood during simulated firefighting in the heat. Participants (N = 10) performed three trials in a counterbalanced order, either with 400 mg caffeine, menthol lozenges, or placebo. The simulated firefighting consisted of 2 bouts of 20-min treadmill exercise and one bout of 20-min stepping exercise in the heat with two brief 15-min rest periods between each exercise phase. Exercise induced significant dehydration (>3%) and elevated rectal temperature (>38.9 °C), for all three conditions. Neither caffeine nor menthol reduced perceived exertion compared to placebo (p > 0.05). Mood ratings (i.e., alertness, hedonic tone, tension) significantly deteriorated over time (p < 0.05), but there was no difference among the three conditions. Simple reaction time, short-term memory, and retrieval memory did not alter with treatments or repeated evaluations. Reaction accuracy from a math test remained unchanged throughout the experimental period; reaction time from the math test was significantly faster after exposure to the heat (p < 0.05). It is concluded that, exhaustive exercise in the heat severely impacted mood, but minimally impacted cognition. These treatments failed to show ergogenic benefits in a simulated firefighting paradigm in a hot environment.     

Evaporative resistance and sustainable work under heat stress conditions for two cloth anticontamination ensembles

When a work scenario in protective clothing is a nominal two hours of work followed by a short break, the level of heat stress must be limited to conditions of thermal equilibrium. By comparing changes in maximum sustainable work rate in a fixed environment, differences due to different protective clothing ensembles can be determined. To illustrate this principle, two protective clothing ensembles were examined. The Basic Ensemble was a cotton blend coverall over gym shorts with hard hat, gloves and full face mask respirator. The Enhanced Ensemble added a light weight, surgical scrub suit under the coveralls, plus a hood worn under the hard hat. Five young, acclimated males were the test subjects. Environmental conditions were fixed at T_db=32°C and T_pwb=26°C. After a physiological steady state was established at a low rate of work, treadmill speed was increased by 0.04 m/s every 5 min. The trial continued until thermal equilibrium was clearly lost. A critical treadmill speed was noted at the point thermal equilibrium was lost for each ensemble and subject. The drop in treadmill speed from the basic to enhanced ensemble was 11%. Based on measured values of average skin temperature and metabolic rate at the critical work rate and estimated values of clothing insulation, the average evaporative resistances for the basic and enhanced ensembles were 0.018 and 0.026 kPa m²/W, respectively.

Relevance to industry

Protective clothing decisions are based on the need to reduce the risk of skin contact with chemical or physical hazards. Sometimes over-protection of the skin results in a hazard secondary to the skin, such as heat stress. With or without over-protection, protective clothing decisions may affect the level of heat stress and result in lower rates of sustainable work. This paper illustrates the affects of a relatively small change in protective clothing requirements on the ability to work in the heat.     

Selected physiological and psychobiological responses to physical activity in different configurations of firefighting gear

The aim was to examine selected physiological and psychobiological responses to different configurations of protective firefighting gear. Career firefighters (n = 10) walked on a treadmill (3·5?km · h^?1, 10% grade) for 15?min in three different clothing configurations. On separate days subjects wore: (a) ‘station blues’, (b) a hip boot configuration of firefighting gear, and (c) the current ‘NFPA 1500 standard’ gear. Physiological, psychophysical, and psychological measurements were recorded pre-exercise (5?min), during exercise (15?min), and during post-exercise recovery (10min). Repeated measures ANOVA revealed significant main effects for condition, time, and interaction (p < 0·001) for heart rate (HR), rectal temperature, mean skin temperature, oxygen consumption, breathing distress, thermal sensations, and affect. Furthermore, post hoc analyses revealed that all variables were significantly higher in the NFPA 1500 standard versus the hip boot or the station blues clothing configurations. These data suggest that the current NFPA 1500 standard configuration results in greater physiological and psychobiological stress at a given workload.     

Heat stress while wearing long pants or shorts under firefighting protective clothing

It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8 km x h(-1), 5% grade), moderate (M, 4.5 km x h(-1), 2.5% grade), light (L, 4.5 km x h(-1)) or very light (VL, 2.5 km x h(-1)) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35 degrees C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (Tre) or heart rate response during heavy or moderate exercise where exposure times were less than 1 h (40.8 +/- 5.8 and 53.5 +/- 9.2 min for H and M, respectively while wearing P, and 43.5 +/- 5.3 and 54.2 +/- 8.4 min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise Tre was reduced by as much as 0.4 degrees C after 80 min of exercise while wearing S. Exposure times were significantly increased from 65.8 +/- 9.6 and 83.5 +/- 11.6 min during L and VL, respectively while wearing P to 73.3 +/- 8.4 and 97.0 +/- 12.5 min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10 - 15% during light exercise. However, during heavier exercise where exposure times were less than 1 h replacing P with S was of little benefit.     

Ergonomics International

It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8?km·h^?1, 5% grade), moderate (M, 4.5?km·h^?1, 2.5% grade), light (L, 4.5?km·h^?1) or very light (VL, 2.5?km·h^?1) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35°C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (T_re) or heart rate response during heavy or moderate exercise where exposure times were less than 1?h (40.8?±?5.8 and 53.5?±?9.2?min for H and M, respectively while wearing P, and 43.5?±?5.3 and 54.2?±?8.4?min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise T_re was reduced by as much as 0.4°C after 80?min of exercise while wearing S. Exposure times were significantly increased from 65.8?±?9.6 and 83.5?±?11.6?min during?L and VL, respectively while wearing P to 73.3?±?8.4 and 97.0?±?12.5?min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10?–?15% during light exercise. However, during heavier exercise where exposure times were less than 1?h replacing P with S was of little benefit.     

Core temperature and heart rate response to repeated bouts of firefighting activities

During live-fire firefighting operations and training evolutions, firefighters often consume multiple cylinders of air and continue to wear their personal protective equipment even after fire suppression activities have ceased. However, most studies have only reported core temperature changes during short-term firefighting activities and have shown a very modest increase in core temperature. Therefore, the purpose of this study is to evaluate core temperature and heart rate (HR) during repeated bouts of firefighting activity over ～3 h. The results of this study show that core temperatures increase by an average of 1.9°C – to a larger magnitude than previously reported – and continue to increase during subsequent work cycles (38.4 vs. 38.7) even after long breaks of more than 30 min. The rate of core temperature increase during work continues to increase later in the training exercise (from 0.036 to 0.048°C/min), increasing the risk for exertional heat stress particularly if long-duration firefighting activity is required at these later times.

Practitioner Summary: To date, core temperature and HR changes during firefighting have been reported for short-term studies, which may significantly underestimate the physiological burden of typical firefighting activities. Firefighter core temperatures are shown to increase to a larger magnitude than previously observed and the rate of rise in core temperature increases during subsequent firefighting activities.     

Evaluation of two cooling systems under a firefighter coverall

Firemen often suffer from heat strain. This study investigated two chest cooling systems for use under a firefighting suit. In nine male subjects, a vest with water soaked cooling pads and a vest with water perfused tubes were compared to a control condition. Subjects performed 30 min walking and 10 min recovery in hot conditions, while physiological and perceptual parameters were measured. No differences were observed in heart rate and rectal temperature, but scapular skin temperature and fluid loss were lower using the perfused vest. Thermal sensation was cooler for the perfused vest than for the other conditions, while the cool pad vest felt initially cooler than control. However, comfort and RPE scores were similar. We conclude that the cooling effect of both tested systems, mainly providing a (temporally) cooler thermal sensation, was limited and did not meet the expectations.     

Comparison of three internationally certified firefighter protective ensembles: Physiological responses,mobility, and comfort

BackgroundFire protective ensembles (FPEs) are essential to safely perform firefighting job tasks; however, they are often burdensome to the workers. The aim of this study was to compare three internationally certified fire protective ensembles from the European Union (EU), South Korea (SK), and United States (US) on physiological responses, mobility, and comfort.MethodsTen male professional firefighters performed a battery of exercises in the laboratory following the ASTM F3031-17 standard to evaluate mobility, occupation-specific performance, and physiological responses (body weight, heart rate (HR), core temperature (T_c), breathing rate (BR), and rating of perceived exertion (RPE)) to 20 min of treadmill walking (3.2 mph, 5% incline). All participants carried out the evaluation wearing each FPE in a random order. Mixed effects models examined time (pre-vs. post-) by ensemble (EU, SK, US) interactions for all physiological variables and compared comfort, performance, and subjective variables across ensembles.ResultsNo interaction effects were observed for body weight, HR, T_c, BR, or RPE (p = 0.890, p = 0.994, p = 0.897, p = 0.435, and p = 0.221; respectively). SK had greater trunk flexion than EU (78.4° vs. 74.6°, p = 0.026) and US had lower standing reach than EU (105.5 cm vs. 115.4 cm, p = 0.004). Agility circuit time was lower in US (9.3 s) compared to EU (9.8 s) or SK (9.9 s) (p = 0.051 and p = 0.019, respectively).ConclusionsThe findings suggest that physiological burden remained largely unchanged across the international FPEs. However, mobility, performance, and comfort may be significantly influenced across types. International stakeholders and end users should consider design implications when choosing fire protective ensembles.     

Reproducibility of body temperature response to standardized test conditions when assessing clothing

Abstract

The traditional use of core temperature to assess the thermal effects of clothing has recently been questioned. The purpose of this study was to assess the reproducibility of body temperature in five subjects (mean age, 226 ± 1-5 yrs) wearing either athletic clothing or a chemical protective overgarment while exercising at 20°C and at 40°C. The exercise was preceded by a 1 h adaptation period in a controlled environmental chamber. Results indicated that mean group change in rectal temperature (δT_r ) appeared to be reproducible for both garment ensembles at 20°C but not at 40°C. For mean change in oesophageal temperature ( δT_oes ) at 20°C, reproducibility was obtained for the overgarment but not for the athletic garment; at 40°C, mean δT_oes appeared to be reproducible with both garments. However, when individual responses were examined, there was little reproducibility for either δT_r or δT_oes . In addition, these measurements failed to show differences in the types of clothing worn. It was concluded that the use of core temperature to assess heat stress imposed by wearing clothing during exercise may lead to erroneous conclusions.     

Physiological strains in hot-humid conditions while wearing disposable protective clothing commonly used by the asbestos removal industry

Abstract

The purpose of this study is to investigate workers' responses to work in hot-humid conditions while wearing protective clothing commonly used by the asbestos removal industry, and to evaluate the effects of resting between work bouts in a cool environment on the physiological strain. Seven male students wearing impermeable protective clothing and air masks were exposed to the following conditions for 100 min on separate days: (1) hot conditions (35°C/85%RH), (2) cool conditions (20°C/85%RH), and (3) hot/cool conditions (working in hot conditions and resting in cool conditions). After 12 min rest, the subjects worked on an ergometer (70 Watts) for 18 min. This experimental schedule was repeated three times under each environmental condition. Rectal temperature (T_π), heart rate (HR), sweat rate (SR) and discomfort sensation were recorded. Two of the subjects were not able to complete the experiment in hot conditions. The increases in T_π and HR with time were not found in cool conditions. Although T_π increased in hot/cool conditions, it was almost half of that in hot conditions. Since HR did not return to the pre-work level during recovery in hot conditions, HR during work was accompanied by increases in HR at pre-work. HR during work in hot/cool conditions was higher than that in cool conditions, HR at pre-work, however, was almost the same as that in cool conditions because of rapid recovery. The means of SR in hot and hot/cool conditions were five and four times greater than that in cool conditions, respectively. Discomfort sensation was improved by resting in cool conditions either at rest in cool conditions or during work in hot conditions. The rate of body heat storage that was calculated at the end of each work and recovery period showed that it was positive even in recovery under the hot conditions. It also presented a significant negative phase in recovery under the hot/cool conditions. Thermal stress was linked to work in protective clothing in hot-humid environments. However, the physiological strains were dramatically ameliorated by resting between work periods in a cool environment. The idea of a ‘cool room’ inside the workplace, so to reduce thermal stress, is proposed.     

The effect of pre-warming on performance during simulated firefighting exercise

This study examined the effect of active pre-warming on speed and quality of performance during simulated firefighting exercise. Twelve male firefighters performed two trials in counterbalanced order. They were either pre-warmed by 20-min cycling at 1.5 Watt kg⁻¹ body mass (WARM) or remained thermoneutral (CON) prior to a simulated firefighting activity. After the pre-warming, gastrointestinal temperature (P < 0.001), skin temperature (P = 0.002), and heart rate (P < 0.001) were higher in WARM than in CON. During the firefighting activity, rating of perceived exertion, thermal sensation and discomfort were higher for WARM than for CON. Finish time of the firefighting activity was similar, but the last task of the activity was completed slower in WARM than in CON (P = 0.04). In WARM, self-reported performance quality was lower than in CON (P = 0.04). It is concluded that pre-warming reduces the speed during the last part of simulated firefighting activity and reduces self-reported quality of performance.     

Application of thermoregulatory modeling to predict core and skin temperatures in firefighters

The purpose of the study was to compare body temperature responses from subjects who exercised while wearing firefighter clothing to predictive data from a real-time thermoregulatory model that had been initially developed and validated for use in the military. Data from two firefighter studies, firefighter study 1 (FFS1: 7 males and 3 females, continuous treadmill exercise at 50% VO_2max, 25 °C, 50% RH) and firefighter study 2 (FFS2: 6 males, intermittent treadmill exercise at 75% VO_2max, 35 °C, 50% RH), were utilized for the thermoregulatory modeling and comparison. The results showed that prediction error (RMSD) of the model for core and skin temperatures was 0.33 and 0.65 °C in FFS1 and 0.39 and 0.86 °C in FFS2, respectively. While the real-time thermoregulatory model tested in the present study showed the potential for providing a means for reasonably accurate prediction of body temperature responses in firefighters, further development on the model's metabolism algorithms to include adjustments for protective clothing, options to facilitate external work, inclusions of cooling effects are suggested.Relevance to industryFirefighters exposed to thermal extremes experience physiological strain, but direct monitoring of physiological variables is not always practical. Thermoregulatory models can simulate the thermal responses reasonably accurately by applying known thermo-physiological mechanisms together with heat loss mechanisms related to clothing and environment in an effort to improve firefighter safety.     

Impact of wet underwear on thermoregulatory responses and thermal comfort in the cold

The purpose of this study was to investigate the significance of wet underwear and to compare any influence of fibre-type material and textile construction of underwear on thermoregulatory responses and thermal comfort of humans during rest in the cold. Long-legged/long-sleeved underwear manufactured from 100% polypropylene in a 1 -by-1 rib knit structure was tested dry and wet as part of a two-layer clothing system. In addition cotton (1-by-l rib knit), wool (1-by-l rib knit), polypropylene (fishnet), and a double-layer material manufactured from 47% wool and 53% polypropylene (interlock knit) was tested wet in the clothing system. In the wet condition 175 g of water was distributed in the underwear prior to the experiment. The test was done on eight men (T_a = 10°C, RH = 85%, V_a < 01 m/s), and comprised a 60min resting period. Skin temperature, rectal temperature, and weight loss were recorded during the test. Total changes in body and clothing weight were measured separately. Furthermore, subjective ratings on thermal comfort and sensation were collected. The tests demonstrated the significant cooling effect of wet underwear on thermoregulatory responses and thermal comfort. Further, the tests showed that textile construction of underwear in a two-layer clothing ensemble has an effect on the evaporation rate from clothing during rest in the cold resulting in a significant difference in mean skin temperature. The thickness of the underwear has more of an influence on the thermoregulatory responses and thermal comfort, than the types of fibres tested.     

Heat stress in chemical protective clothing: porosity and vapour resistance

Heat strain in chemical protective clothing is an important factor in industrial and military practice. Various improvements to the clothing to alleviate strain while maintaining protection have been attempted. More recently, selectively permeable membranes have been introduced to improve protection, but questions are raised regarding their effect on heat strain. In this paper the use of selectively permeable membranes with low vapour resistance was compared to textile-based outer layers with similar ensemble vapour resistance. For textile-based outer layers, the effect of increasing air permeability was investigated. When comparing ensembles with a textile vs. a membrane outer layer that have similar heat and vapour resistances measured for the sum of fabric samples, a higher heat strain is observed in the membrane ensemble, as in actual wear, and the air permeability of the textile version improves ventilation and allows better cooling by sweat evaporation. For garments with identical thickness and static dry heat resistance, but differing levels of air permeability, a strong correlation of microclimate ventilation due to wind and movement with air permeability was observed. This was reflected in lower values of core and skin temperatures and heart rate for garments with higher air permeability. For heart rate and core temperature the two lowest and the two highest air permeabilities formed two distinct groups, but they did not differ within these groups. Based on protection requirements, it is concluded that air permeability increases can reduce heat strain levels allowing optimisation of chemical protective clothing. STATEMENT OF RELEVANCE: In this study on chemical, biological, radiological and nuclear (CBRN) protective clothing, heat strain is shown to be significantly higher with selectively permeable membranes compared to air permeable ensembles. Optimisation of CBRN personal protective equipment needs to balance sufficient protection with reduced heat strain. Using selectively permeable membranes may optimise protection but requires thorough consideration of the wearer's heat strain.     

Cardiovascular and thermal consequences of protective clothing: a comparison of clothed and unclothed states

We have undertaken a laboratory-based examination of the cardiovascular and thermal impact of wearing thermal (heat) protective clothing during fatiguing exercise in the heat. Seven males completed semi-recumbent, intermittent cycling (39.6 degrees C, 45% relative humidity) wearing either protective clothing or shorts (control). Mean core and skin temperatures, cardiac frequency (f(c)), stroke volume (Q), cardiac output (Q), arterial pressure, forearm blood flow (Q(f)), plasma volume change, and sweat rates were measured. In the clothed trials, subjects experienced significantly shorter times to fatigue (52.5 vs. 58.9 min), at lower peak work rates (204.3 vs. 277.4 W), and with higher core (37.9 degrees vs. 37.5 degrees C) and mean skin temperatures (37.3 degrees vs. 36.9 degrees C). There was a significant interaction between time and clothing on f(c), such that, over time, the clothing effect became more powerful. Clothing had a significant main affect on Q, but not Q, indicating the higher Q was chronotropically driven. Despite a greater sweat loss when clothed (923.0 vs. 547.1 g.m(-2) x h(-1); P<0.05), Q(f) and plasma volume change remained equivalent. Protective clothing reduced exercise tolerance, but did not affect overall cardiovascular function, at the point of volitional fatigue. It was concluded that, during moderately heavy, semi-recumbent exercise under hot, dry conditions, the strain on the unclothed body was already high, such that the additional stress imparted by the clothing ensemble represented a negligible, further impact upon cardiovascular stability.     

The impact of various rehydration volumes for firefighters wearing protective clothing in warm environments

This study examined different fluid replacement quantities during intermittent work while wearing firefighting protective clothing and self-contained breathing apparatus in the heat (35 degrees C, 50% relative humidity). Twelve firefighters walked at 4.5 km per h with 0% elevation on an intermittent work (50 min) and rest (30 min) schedule until they reached a rectal temperature of 39.5 degrees C during work periods and 40.0 degrees C during rest, heart rates of 95% of maximum and/or exhaustion. During the heat-stress trials subjects received one of four fluid replacement quantities, high (H), moderate (M), low (L), and no hydration (NH), where H, M and L represented 78%, 63% and 37% of fluid loss, respectively. The total tolerance time (work + rest) was significantly greater during H (111.8 +/- 3.5), M (112.9 +/- 5.2) and L (104.2 +/- 5.8) compared to NH (95.3 +/- 3.8). In addition, work time (min), which excluded rest periods, was significantly greater in H (82.6 +/- 3.5), and M (82.9 +/- 5.2) compared to NH (65.3 +/- 3.8). It is concluded that incorporating even partial fluid replacement strategies while wearing firefighting protective clothing and self-contained breathing apparatus in the heat improves tolerance time.     

The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat

This study investigated the effects that a form fitted, moisture-wicking fabric shirt, promoted to have improved evaporative and ventilation properties, has on the physiological and perceptual responses during exercise in the heat. Ten healthy male participants completed two heat stress tests consisting of 45 min of exercise (50% VO_2peak) in a hot environment (33 °C, 60% RH). One heat stress test was conducted with the participant wearing a 100% cotton short sleeved t-shirt and the other heat stress test was conducted with the participant wearing a short sleeved synthetic shirt (81% polyester and 19% elastane). Rectal temperature was significantly lower (P < 0.05) in the synthetic condition during the last 15 min of exercise. Furthermore, the synthetic polyester shirt retained less sweat (P < 0.05). As exercise duration increases, the ventilation and evaporation properties of the synthetic garment may prove beneficial in the preservation of body temperature during exercise in the heat.     

The impact of various rehydration volumes for firefighters wearing protective clothing in warm environments

This study examined different fluid replacement quantities during intermittent work while wearing firefighting protective clothing and self-contained breathing apparatus in the heat (35°C, 50% relative humidity). Twelve firefighters walked at 4.5 km per h with 0% elevation on an intermittent work (50 min) and rest (30 min) schedule until they reached a rectal temperature of 39.5°C during work periods and 40.0°C during rest, heart rates of 95% of maximum and/or exhaustion. During the heat-stress trials subjects received one of four fluid replacement quantities, high (H), moderate (M), low (L), and no hydration (NH), where H, M and L represented 78%, 63% and 37% of fluid loss, respectively. The total tolerance time (work + rest) was significantly greater during H (111.8 ± 3.5), M (112.9 ± 5.2) and L (104.2 ± 5.8) compared to NH (95.3 ± 3.8). In addition, work time (min), which excluded rest periods, was significantly greater in H (82.6 ± 3.5), and M (82.9 ± 5.2) compared to NH (65.3 ± 3.8). It is concluded that incorporating even partial fluid replacement strategies while wearing firefighting protective clothing and self-contained breathing apparatus in the heat improves tolerance time.