Applied Ergonomics xxx (2014) 1e7
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The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat Justin De Sousa*, Christopher Cheatham, Matthew Wittbrodt 1 Western Michigan University, 1903 W. Michigan Ave, Kalamazoo, MI 49008, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 October 2013 Accepted 6 April 2014 Available online xxx
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% VO2peak) 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. Ó 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Keywords: Clothing Heat Exercise
1. Introduction Strenuous exercise in combination with environmental heat stress significantly impacts fatigue, diminishing exercise performance (Gisolf and Wenger, 1984; Gonzalez-Alonso et al., 1999; Hargreaves, 2008; Sawka et al., 2011) and increasing the risk of heat-related injury (Gonzalez-Alonso et al., 1999; Hargreaves, 2008; Periard et al., 2011). Increased cardiovascular strain resulting from hyperthermia reduces maximal cardiac output (Cheuvront et al., 2010; Gonzalez-Alonso et al., 2008; Hargreaves, 2008), mean arterial pressure (Gonzalez-Alonso and Calbet, 2003; Hargreaves, 2008), oxygen delivery (Fink et al., 1975; Gonzalez-Alonso et al., 2008), overall oxygen uptake (Cheuvront et al., 2010; Fink et al., 1975; Gonzalez-Alonso and Calbet, 2003; Periard et al., 2011) and central neuromuscular drive (Cheung and Sleivert, 2004). Therefore, optimizing tolerance in the heat through attenuating heat stress by balancing metabolic heat gain with heat loss becomes a central focus in maintaining performance and safety (Cheuvront et al., 2010). One distinct method utilized in an attempt to mitigate heat stress and improve heat tolerance is the employment of clothing with properties that positively augment heat dissipation
* Corresponding author. Tel.: þ1 269 365 8509. E-mail addresses: [email protected] (J. De Sousa), chris.cheatham@ wmich.edu (C. Cheatham), [email protected] (M. Wittbrodt). 1 Georgia Institute of Technology, 225 North Ave NW, Atlanta, GA 30332, USA.
from the exercising body to the external environment (Wendt et al., 2007). The design and fabric are principal factors that influence a garment’s insulation and air permeability properties, which subsequently affect heat transfer (Woodcock, 1962). The use of clothing provides a layer of insulation and a barrier between the skin and the environment (Gavin, 2003). Wool and cotton garments have high sorption properties, causing the fabric to hold sweat, which may lead to decreased comfort and impaired heat dissipation as a result of decreased evaporation of sweat (Dai et al., 2008). Conversely, synthetic polyester garments have been suggested to improve sweat evaporation, due to increased fabric permeability, possibly leading to a lower core temperature (Gavin et al., 2001; Woodcock, 1962). Athletes have utilized clothing from athletic apparel companies who market the garments’ effects on limiting heat stress by keeping the athlete cool and dry, citing improved ventilation and evaporative characteristics. However, whether these synthetic polyester garments have a significant effect on the physiological and perceptual responses during exercise in the heat still remains unclear and current research has demonstrated inconclusive evidence. A study by Gavin et al. (2001) revealed no alterations in physiological or perceptual responses during exercise of eight highly trained athletes in a warm environment with clothing conditions consisting of a short sleeved cotton and synthetic polyester shirt. The researchers suggested that the exercise intensity of 70% VO2peak
http://dx.doi.org/10.1016/j.apergo.2014.04.006 0003-6870/Ó 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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for 30 min may not have been significant enough to stress the highly trained participants. As a result, the exercise intensity and duration may have failed to adequately stress the participants’ thermoregulatory systems, negating any impact of clothing. In a follow-up study utilizing similar environmental and clothing conditions, Brazaitis et al. (2010) found that higher exercise intensities revealed better sweat evaporation and reduced sweat sorption in participants wearing the polyester garments. However, no differences in the two garments for any thermo-physiological or subjective comfort responses were observed. While Gavin et al. (2001) reported that their study may have been limited by an exercise intensity and duration that was too low in relation to the training level of their participants, Brazaitis et al. (2010) did not measure the aerobic capacity of their participants. This would make it difficult to assess whether the assigned absolute workload was an intense level of physical activity for all eight participants. Therefore the absolute treadmill workload of 5 mph at 1% grade may have fell short of their desired intensity range. Even with each participant performing three 20-min bouts of exercise with five minutes of rest, the physiological stress of the exercise intensity would be different for each participant and highly dependent on their aerobic capacity. This would make it problematic to elucidate clothing’s impact on thermoregulation at a specific intensity of exercise. For this reason, quantifying the stress relative to an individual’s physiological system would better establish equivalent exercise intensities among participants (McArdle et al., 2007). Therefore, the aim of the present is to 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 moderate intensity exercise in the heat. To the best of our knowledge, no study has explored this in recreationally active participants using a prolonged, continuous exercise protocol that establishes exercise intensity as a percent of their current aerobic capacity. 2. Material and methods 2.1. Participants Ten recreationally active male participants (Age: 24.5 3.5 yrs, Height: 179.8 0.1 cm, VO2peak: 42.4 6 mL kg1 min1, Body Weight: 90.8 13.1 kg, Body Mass Index: 27.9 3.8 kg m2, Body Fat: 15.4 6.0%) participated in this study. All participants were healthy, free of disease and medication use, not obese (Body Mass Index < 30.0 kg m2), and non-smokers. The study was approved by the Human Participants Institutional Review Board at Western Michigan University. All participants read and signed the informed consent prior to participation in the study. 2.2. Research design Each participant visited the human performance research laboratory on three separate occasions. During the first visit, anthropometric measurements were obtained and each participant performed a maximal graded exercise test on a cycle ergometer. On the second and third visits, a heat stress test was performed. One heat stress test was conducted with the participant wearing a nonform fitted, 100% cotton, short sleeved t-shirt (COT) and the other heat stress test was conducted with the participant wearing a short sleeved, form fitted, commercially available, synthetic shirt (81% polyester and 19% elastane) (SYN). The SYN shirt was promoted by the manufacturer to be moisture wicking and have enhanced air permeability due to a ventilated mesh back. The COT and SYN shirts were fitted to cover the same skin surface area and each participant
wore the same athletic shoes, ankle socks and knee length shorts (top of the patella) during both heat stress tests. The order of the heat stress tests was counter-balanced and each participant finished the study in a four week time period. Prior to each visit, participants were instructed to refrain from alcohol, caffeine, and physical activity the day before and the day of the visits to the laboratory. 2.2.1. Anthropometric assessment and graded exercise test Upon arrival to the laboratory on the first day, all research procedures were explained to the participants and informed consent was obtained. Each participant then completed a health history questionnaire in order to confirm that they were healthy, free of disease and medication use, and classified as “low-risk” according to the American College of Sports Medicine (ACSM) guidelines (2010). Each participant then had their anthropometric measurements assessed. Weight and height were measured via a digital scale (Totalcomp, Fair Lawn, NJ) and stadiometer (Seca Instruments Ltd, Hamburg, Germany), respectively. Skinfold thickness was measured at seven sites (triceps, abdomen, thigh, calf, suprailiac, chest, subscapular) using skinfold calipers (Lange, Beta Technology Inc. Cambridge, MD). Each site was measured three times with the mean of the three measurements used as the skinfold thickness. The Jackson & Pollock 7-site equation was used to calculate body density from the skinfold assessment and the Brozek equation was used to calculate percent body fat from body density (Brozek et al., 1963; Jackson and Pollock, 1985). Upon completion of the anthropometric assessment, the participant completed a graded exercise test on a cycle ergometer (Corival, Lode B.V., Groningen, Netherlands) to determine VO2peak. Prior to all tests, the metabolic cart was calibrated using a 3-L syringe and gases of known concentration. Each participant was then fitted with a nose clip and a mouthpiece for the collection of expired respiratory gases using the metabolic measurement cart (TrueOne 2400, ParvoMedics, Sandy, UT) and a telemetry heart rate (HR) monitor (Polar USA, Lake Success, Long Island, NY). Lastly, each participant was instructed on using the Borg Ratings of Perceived Exertion (RPE) chart (Morgan and Borg, 1976). Once instrumentation of the participant was complete, the exercise test began. The graded exercise test started at 60 Watts for 2 min and then exercise intensity was increased 20 W every minute until volitional fatigue. VO2peak was defined as the greatest 30-sec average during the test. 2.2.2. Heat stress tests During the second and third visits to the laboratory, each participant completed a heat stress test (COT or SYN). To ensure hydration, each participant was instructed to consume w6e8 mL of water per kilogram of body weight 2 h prior to testing. Upon arrival to the laboratory, each participant was instructed to void and nude body weight was measured. Each participant was then instructed to insert a rectal temperature probe (Physitemp Instruments Inc., Clifton, NJ) 13 cm past the anal sphincter. After insertion of the rectal probe, skin thermocouples (Physitemp Instruments Inc., Clifton, NJ) were attached to the right side of the body at the chest, triceps, thigh and calf with waterproof tape (Hytape, Hytape International Inc., Patterson, NY) for determination of mean skin temperature (MTsk) (Ramanathan, 1964). It is important to note that the chest and triceps skin thermocouples were covered by the shirt in both conditions. Rectal and skin thermocouples were interfaced to a data acquisition system (Thermes USB, Physitemp Instruments Inc., Clifton, NJ), which was linked to a PC computer. For the determination of sweat volumes an automated resistance hygrometry system (QSweat, WR Medical Electronics Co.,
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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Stillwater, MN) was utilized (Bullard, 1962). Ventilated capsules (0.787 sq cm) were secured with rubber straps to the upper chest, back, thigh, and forearm and then interfaced to a PC for the continuous collection of sweat volume. A telemetry HR monitor was strapped around the participant’s chest for the measurement of HR. Lastly, the participant’s shirt was weighed (LC101, Omega Engineering Inc., Stamford, CT) and then placed on the individual before they were seated on a lounge chair in a semi-recumbent position. Once instrumentation of the participant was completed, the participant sat quietly for 20 min in a thermo-neutral environment (24 C, 60% RH) (24 CBASE), followed by 30 min of seated rest in a heated environment (33 C, 60% RH) (33 CBASE). Rectal temperature (Tre), skin temperatures and sweat rate (SR) were measured continuously. Thermal sensation (Gagge et al., 1967), sweating sensation (Gavin et al., 2001), RPE and HR were assessed during the last minute of 24 CBASE and 33 CBASE. After completion of 33 CBASE, the participant was transported to the electronically braked cycle ergometer and began the exercise portion of the trial. Exercise consisted of cycling for 45 min at 50% VO2peak in 33 C air and 60% RH (33 CEX). Expired respiratory gases were assessed during 0e15 min, 25e30 min and 40e45 min of exercise. During minutes 5e7 of exercise, if the participant was not within 5% of the desired 50% VO2peak, workload adjustments were made to elicit the desired exercise intensity. This workload was then replicated during the participant’s second trial. Rectal temperature, skin temperatures and SR were measured continuously during exercise. HR, RPE, thermal sensation, and sweat sensation were recorded every 5 min. Water intake was monitored and measured. Each participant was permitted to consume water ad libitum during the first heat stress test. To control for hydration status between the two heat stress test fluid consumption during session two mimicked the initial heat stress test. At the completion of each heat test, the participant’s garment was immediately placed in the same freezer bag, sealed and weighed. All probes and capsules were removed and the participant was instructed to towel off and weigh them self nude.
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To analyze the difference between the COT and SYN apparel shirts for shirt weight and whole-body sweat volume and rate, a paired samples t-test was used. The level of statistical significance was established a priori as P < 0.05. The SPSS statistical package (v17.0) was used for data analysis. Data is presented as means (M) standard deviations (SD). 3. Results 3.1. Physiological variables 3.1.1. Exercise intensity There was no significant difference in workload between the clothing conditions (P ¼ 0.989). Mean exercise intensity (L min1) was 1.90 0.29 (50.2 3.4 %VO2Peak) in the COT clothing condition and 1.88 0.40 (50.1 1.6 %VO2Peak) in the SYN clothing condition. 3.1.2. Rectal temperature The response in Tre over time during the COT and SYN clothing conditions is displayed in Fig. 1. As expected, there was a significant main effect for time (P < 0.001) in that there was a progressive increase from 33 CBASE to the end of 33 CEX. Overall, there was no significant difference between the clothing conditions (COT: 37.54 0.34, SYN: 37.42 0.27 C; P ¼ 0.065), although the clothing-by-time interaction was significant (P ¼ 0.001). Post-hoc testing revealed that Tre was greater during COT compared to SYN during the last 15 min of exercise. 3.1.3. Skin temperature The response in MTsk over time in the COT and SYN clothing conditions is demonstrated in Fig. 2. Similar to the results reported above for Tre, there was a significant main effect for time (P < 0.001) with MTsk progressively increasing with the duration of the trial. Overall, there was no significant difference between the clothing conditions (COT: 35.77 1.13, SYN: 35.83 0.90 C; P ¼ 0.762) and
2.3. Calculations 2.3.1. Mean skin temperature MTsk was calculated using the weighting formula: MTsk ( C) ¼ (0.28 * Tchest) þ (0.08 * Ttricep) þ (0.28 þ Tthigh) þ (0.22 * Tcalf) þ (0.14 * Tforearm) (Toner et al., 1986). 2.3.2. Sweat volumes, whole body sweat loss and shirt weight Cumulative sweat volume was calculated as the sum of sweat produced in mL cm2 during 24 CBASE, 33 CBASE and 33 CEX. Whole body sweat loss was calculated as the difference between pre and post body weight, plus the amount of fluid consumed during the trial. Shirt weight difference was calculated as the difference between shirt weight pre and post exercise. 2.4. Statistical analysis To analyze the differences between the COT and SYN apparel shirts for temperature, sweat volume and rate, HR and perceptual data, a two-way analysis of variance (ANOVA) with repeated measures was utilized. The factors in the analysis were clothing (COT vs. SYN) and time with both being repeated measures. In the case of a significant main effect for time or interaction, post-hoc tests were performed using a simple effects analysis with the Bonferroni adjustment.
Fig. 1. The response in rectal temperature during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions at all times points, p < 0.001. No significant differences between conditions, p ¼ 0.065. *, Indicates a significant difference in the clothing-by-time interaction between COT and SYN, p < 0.05.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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difference between the clothing conditions (COT: 124 5, SYN: 119 5 beats min1; P ¼ 0.127). As expected, there was a significant main effect for time (P < 0.001). The clothing by time interaction was not significant (P ¼ 0.370). 3.2. Perceptual variables 3.2.1. Thermal sensation Fig. 5 displays the response in thermal sensation over time in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions (COT: 5.8 1.0, SYN: 5.6 0.9; P ¼ 0.320). As expected, there was a significant main effect for time (P < 0.001). Post-hoc testing revealed a significant difference in 24 CBASE vs. 33 CBASE and all exercise time points and 33 CBASE vs. all exercise time points. The clothing by time interaction was not significant (P ¼ 0.990).
Fig. 2. The mean skin temperature response during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions at all times points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothingby-time interaction, p > 0.05.
the clothing-by-time interaction (P ¼ 0.165). However, it is important to indicate that the clothing-by-time interaction was significant for skin temperature at the chest (P ¼ 0.001). Post-hoc testing revealed that Tchest was greater during COT compared to SYN at 25, 40, and 45 min exercise. 3.1.4. Cumulative sweat volume Fig. 3 displays the response in cumulative sweat volume in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions with respect to cumulative sweat volume at the chest (COT: 50.02 15.11, SYN: 43.13 15.25 mL cm2; P ¼ 0.120), back (COT: 53.37 20.33, SYN: 52.1 26.68 mL cm2; P ¼ 0.843), thigh (COT: 31.77 12.07, SYN: 33.04 12.07 mL cm2; P ¼ 0.934) and forearm (COT: 35.58 17.79, SYN: 35.58 17.80 mL cm2; P ¼ 0.562). As expected, there was a significant main effect for time for cumulative sweat volume (P < 0.001) at the chest, back, thigh and forearm. Post-hoc testing revealed that all time points for chest, back, thigh and forearm were significantly different from each other. The clothing-by-time interaction was not significant for cumulative sweat volume at the chest (P ¼ 0.076), back (P ¼ 0.947), forearm (P ¼ 0.730) and thigh (P ¼ 0.992).
3.2.2. Sweat sensation Fig. 6 displays the response in sweat sensation over time in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions (COT: 3.5 1.4, SYN: 3.5 1.4; P ¼ 0.702). As expected, there was a significant main effect for time (P < 0.001). Post-hoc testing revealed a significant difference in 24 CBASE vs. 33 CBASE and all exercise time points and 33 CBASE vs. all exercise time points. The clothing by time interaction was not significant (P ¼ 0.876). 3.2.3. Perceived exertion Fig. 7 displays the response in perceived exertion over time in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions (COT: 10.1 2.9, SYN: 9.8 2.8; P ¼ 0.400). As expected, there was a significant main effect for time (P < 0.001). Post-hoc testing revealed a significant difference in 24 CBASE vs. 33 CBASE and all exercise time points and 33 CBASE vs. all exercise time points. The clothing by time interaction was not significant (P ¼ 0.655).
3.1.5. Whole body sweat loss and changes in shirt weight The response in whole body sweat loss over time in conjunction with body weight and shirt weight difference pre-24 CBASE to post-33 CEX in COT and SYN is displayed in Table 1. Overall, there was no significant difference between the clothing conditions with respect to whole body sweat loss (P ¼ 0.396) and body weight differences pre-24 CBASE to post-33 CEX (P ¼ 0.152). However, there was a significant difference in shirt weight (P ¼ 0.05) between pre-24 CBASE and post-33 CEX. 3.1.6. Heart rate The response in HR over time in the COT and SYN clothing conditions is displayed in Fig. 4. Overall, there was no significant
Fig. 3. The cumulative sweat volume during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions at the chest, back, thigh and forearm, p < 0.001. Significant differences at the chest, back, thigh and forearm during both conditions, p < 0.05. No significant difference in the clothing-by-time interaction at the chest, back, thigh and forearm, p > 0.05.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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Table 1 Body weight/shirt weight difference and total body sweat loss during heat stress tests.
Whole body sweat loss (mL) Pre and post BW difference (g) Shirt weight difference (g)
COT
SYN
1284.6 120.1 1028.0 383.1 123.6 14.0
1182.6 89.4 826 305.6 100.6 8.9a
Note: Whole body sweat loss was calculated as the difference between pre- and post-body weight, plus the amount of fluid consumed during the trial. a denotes significant differences between SYN and COT conditions.
4. Discussion This study aimed to investigate the effects that a form fitted, moisture-wicking fabric shirt, promoted to have improved evaporative and ventilation properties, has on the thermoregulatory, physiological and perceptual responses during moderate intensity exercise in the heat. An exercise protocol of 50% VO2peak for 45 min in environmental conditions of 33 C/60% RH was selected in order to impose a heat load significant enough to stress the thermoregulatory system of the recreationally active participants and to simulate conditions often imposed on an individual while aerobically training in the summer. Furthermore, the protocol was utilized to produce a sufficient heat load where the moisturewicking fabric shirt may prove beneficial in the maintenance of body temperature and performance without providing a metabolic load so severe that fatigue sets in too early, not stressing the thermoregulatory system adequately (Gavin et al., 2001). The most interesting finding in the present study is that during the last 15 min of exercise Tre was significantly lower in SYN compared to COT. This is inconsistent with previous research investigating garment effects on Tre during exercise in similar environments (Brazaitis et al., 2010; Gavin et al., 2001). Gavin et al. (2001) reported no significant difference in Tre when examining the difference between polyester and cotton garments (shortsleeved t-shirts, shorts and socks) on thermoregulation during
Fig. 4. The heart rate response during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
Fig. 5. The thermal sensation during the heat stress tests. Values are displayed as means SD. Main effect for time between 24 CBASE and 33 CBASE, 24 CBASE and all exercise time points and 33 CBASE and all exercise time points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
exercise in 30 C and 35% RH air. Gavin et al. (2001) utilized an intensity of 70% VO2peak for 30 min in highly trained aerobic athletes (VO2peak of 67.5 1.4 mL kg1 min1), which may not have produced a significant enough stress in relation to participant training status. Similarly, Brazaitis et al. (2010) found no significant
Fig. 6. The sweat sensation during the heat stress tests. Values are displayed as means SD. Main effect for time between 24 CBASE and 33 CBASE, 24 CBASE and all exercise time points and 33 CBASE and all exercise time points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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Fig. 7. The perceived exertion during the heat stress tests. Values are displayed as means SD. Main effect for time between 24 CBASE and 33 CBASE, 24 CBASE and all exercise time points and 33 CBASE and all exercise time points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
difference in Tre, while evaluating the effects that two kinds of longsleeved t-shirts (94% cotton/6% elastane; 93% polyester/7% elastane) have on the thermoregulatory response during exercise (8 km/h at 1 grade on a treadmill) in a warm and humid environment (25 C and 60% RH). In the present study, a mesh back in the SYN condition, but not in the COT condition, may have resulted in greater ventilation due to higher air permeability, contributing to the observed differences in Tre. The polyester garments in both the Brazaitis et al. (2010) and Gavin (2003) studies were not reported to have a ventilated mesh back, possibly explaining why no difference in Tre was found. Zhang et al. (2002) demonstrated that clothing with high air permeability resulted in significantly lower Tre during exercise in the heat with wind, but not without wind. Likewise, Brownlie et al. (1987) found that clothing with limited vapor permeability caused a significant increase in Tre during exercise in the heat with wind. In the present study wind was not utilized, although it can be inferred that the use of wind would further reduce Tre in the SYN condition because of its superior permeability properties. Clothing with increased air permeability will increase heat loss via convection as the wind carries away warm air surrounding the body (Zhang et al., 2002; Bouskill et al., 2002). Increases in air movement by wind or the movement of the body will facilitate heat dissipation in both conditions, but an even greater affect would result in the SYN condition due to its superior permeability. The COT fabric’s higher absorption and reduced permeability creates a thicker ‘still air barrier’ between the skin and the environment (Woodcock, 1962). This could lead to decreases in dry heat transfer and a possible rationale for an increase in Tre. There was no significant difference in cumulative sweat volume at the chest, back, forearm and thigh, suggesting that clothing of different fabric and characteristics may not affect sweat loss. This is in contrast to Ha et al. (1999), who found that fabrics with high air permeability and moisture regain had lower sweat rates during intermittent exercise (30% VO2peak) at 27 C. Similarly, Kwon et al. (1998) reported greater sweat rates in participants wearing a
long-sleeve 100% polyester shirt compared to a long sleeved 100% cotton shirt during intermittent exercise at 40% VO2peak in 30 C. The intermittent nature of the exercise combined with moisture regain properties of the fabric may be credited for the differences in sweat rate observed in the previously mentioned studies and the present one. Cotton fabrics have high sorption properties (Dai et al., 2008); therefore during periods of rest, the increased wetness of the cotton fabric may have cooled the skin and decreased overall sweat rate. Thermal conductivity has been shown to increase in clothes with high regain properties. This would result in a decrease in the temperature within the clothing microclimate and possible chilling of the participant (Satsumoto et al., 2009). Brazaitis et al. (2010) found that during post-exercise recovery MTsk tended to decline to lower than pre-exercise levels in participants wearing cotton shirts compared to polyester ones, revealing the ability of clothing with high regain properties to cool the skin in a rested state. The use of a continuous protocol in the present study would have assuaged the conductive heat loss from a cool and saturated garment on the skin, possibly increasing reliance on the evaporation of sweat for heat dissipation. Furthermore, Ha et al. (1999) postulated that a lower sweat rate may be due to the combined effects of moisture regain and air permeability, which may be acceptable, since the present study reveals that these properties have no effect on sweat rate independent of each other. The cotton shirt retained a significantly greater amount of sweat than the SYN shirt. This exhibits the high sorption property of the cotton fabric and increased ability of the SYN to promote greater evaporation of sweat. These findings agree with other studies utilizing similar protocols and environmental conditions (Gavin et al., 2001; Brazaitis et al., 2010). Gavin et al. (2001) and Brazaitis et al. (2010) both demonstrated properties of less sweat sorption in the polyester condition with no impact on temperature regulation during exercise in the heat. The increased moisture-wicking ability of the SYN condition did not subsequently alter body weight loss as no significant difference was observed, further reinforcing the notion that the reduced weight of the SYN shirt was due to its greater evaporative characteristics. An increase in exercise duration may prove beneficial to future research. In the present study, as exercise duration progressed there was a main effect between COT and SYN with respect to Tre. It is possible that the evaporative fabric plays a larger role in the maintenance of core temperature during prolonged exercise in the heat (>45 min). The relationship between increasing core temperature and decreasing exercise capacity has been demonstrated in previous research (Galloway and Maughton, 1997). If the observed trend continued past 45 min of exercise, the SYN garment may prove beneficial in reducing the possibility of heat related illness and in the maintenance of aerobic performance during prolonged exercise in the heat. The ability of the SYN to retain less moisture and evaporate sweat more efficiently may reduce the overall heat load on the body by being less of a barrier and allowing for greater heat dissipation to the environment. It should also be noted that rectal temperature has been shown to lag behind core temperature (Sparling et al., 1993). Therefore, similarities in Tre between conditions may have resulted, if exercise progressed beyond 45 min. In both conditions HR quickly increased within the first five minutes of exercise before leveling off with gradual increases until the cessation of exercise. Overall, there was no significant difference between clothing conditions, possibly due to the equivalent amount of participant fluid loss and comparable exercise intensity. Therefore, despite a difference in garment fabric and properties a uniform cardiovascular stress was observed between trials. These findings are similar to Gavin et al. (2001), who found no significant difference in HR between cotton and polyester garments during exercise in the heat. Conversely, Ha et al. (1995) found that
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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participants wearing polyester garments had a higher HR than those wearing cotton garments during intermittent exercise (30% VO2peak) at 27 C. The researchers cited reduced thermal insulation due to absorption of moisture by the cotton fabric as the cause for accelerated heat loss and lower HR. However, the increase in moisture absorption because of high regain properties in the cotton garment would allow for delayed evaporative cooling during the recovery phase. This was not observed in the Gavin et al. (2001) and present studies, which employed continuous exercise. Interestingly, and contrary to Ha et al. (1995), Brazaitis et al. (2010) did not observe any difference in HR between conditions during intermittent exercise or during 60 min of seated recovery. Exercise in the heat at a constant intensity is associated with an increase in RPE as duration progresses (Gonzalez-Alonso et al., 1999). Both the COT and SYN conditions followed similar trends of steadily increasing with exercise duration. However, no significant difference in RPE was attributed to the type of garment worn. Similarly, perception of skin wetness and thermal comfort did not differ with respect to both conditions. Even though the COT fabric absorbed more moisture and weighed more than the SYN, it did not alter the participant’s perception to thermal comfort, sweat sensation or perceived exertion. This agrees with Gavin et al. (2001) and Brazaitis et al. (2010), who found no differences in thermal comfort and sweat sensation between exercise ensembles at any time point, despite the cotton shirt absorbing significantly more sweat from pre to post exercise. It appears that the sorption properties and type of garment fabric plays no role in the perception of thermal comfort, sweat sensation and exertion during exercise in the heat. In conclusion, the form fitted, moisture-wicking fabric shirt, promoted to have improved evaporative and ventilation properties produced a significantly lower Tre during the last 15 min of exercise when compared to a cotton garment. The synthetic polyester shirt exhibited superior evaporative characteristics and lower regain qualities. Moreover, as exercise duration increases, the SYN shirt may prove beneficial in the preservation of body temperature, thus reducing the likelihood of heat related illness and maintaining exercise performance in the heat.
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Cheuvront, S.H., Kenefick, S.J., Moutain, S.J., Sawka, M.N., 2010. Mechanism of aerobic performance impairments with heat stress and dehydration. J. Appl. Physiol. l09 (6), 1989e1995. PMID: 206898090. Dai, X.Q., Imamura, R., Liu, G.L., Zhou, F.P., 2008. Effect of moisture transport on microclimate under t-shirts. Eur. J. Appl. Physiol. 104 (2), 337e340. PMID: 18071744. Fink, W.J., Costill, D.L., Van Handel, P.J., 1975. Leg muscle metabolism during exercise in the heat and cold. Eur. J. Appl. Physiol. 34 (3), 183e190. PMID: 1181181. Gagge, A.P., Stolwijk, A.J., Hardy, J.D., 1967. Comfort and thermal sensation associated with physiological responses at various ambient temperatures. Environ. Res. 1 (1), 1e20. PMID: 5614624. Galloway, S.D., Maughton, R.J., 1997. Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man. Med. Sci. Sports Exerc. 29 (9), 1240e1249. PMID: 9309637. Gavin, T., 2003. Clothing and thermoregulation during exercise. Sports. Med. 33 (13), 941e947. PMID: 14606923. Gavin, T., Babington, P., Harms, C., Ardelt, M., Tanner, D., Stager, J., 2001. Clothing fabric does not affect thermoregulation during exercise in moderate heat. Med. Sci. Sports. Exerc. 33 (12), 2124e2130. PMID: 11740309. Gisolf, C.V., Wenger, C.B., 1984. Temperature regulation during exercise: Old concepts, new ideas. Exerc. Sport. Sci. Rev. 12, 339e372. PMID: 6376137. Gonzalez-Alonso, J., Calbet, J.A.L., 2003. Reductions in systemic and skeletal muscle blood flow and oxygen delivery limit maximal oxygen capacity in humans. CIRC 107 (6), 824e830. PMID: 12591751. Gonzalez-Alonso, J., Teller, C., Andersen, S., Jensen, F., Hyldig, T., Nielsen, B., 1999. Influence of body temperature on the development of fatigue during prolonged exercise in the heat. J. Appl. Physiol. 86 (3), 1032e1039. PMID: 10066720. Gonzalez-Alonso, J., Crandall, C.G., Johnson, J.M., 2008. The cardiovascular challenge of exercising in the heat. J. Physiol. 586 (1), 45e53. PMID: 17855754. Ha, M., Yamashita, Y., Tokura, H., 1995. Effects of moisture absorption by clothing on thermal responses during intermittent exercise at 24 C. Eur. J. Appl. Physiol. 71 (2e3), 266e271. PMID: 7588699. Ha, M., Tokura, H., Yanai, Y., Moriyama, T., Tsuchiya, N., 1999. Combined effects of fabric air permeability and moisture absorption on clothing microclimate and subjective sensation during intermittent exercise at 27 C. Ergon 42 (7), 964e 979. PMID: 10424185. Hargreaves, M., 2008. Physiological limits to exercise performance in the heat. J. Sci. Med. Sport 11 (1), 66e71. PMID: 17720623. Jackson, A.S., Pollock, M.L., 1985. Practical assessment of body composition. Physician. Sport. Med. 13, 76e90. Kwon, A., Kato, M., Kawamura, H., Yanai, Y., Tokura, H., 1998. Physiological significance of hydrophilic and hydrophobic textile materials during intermittent exercise in humans under the influence of warm ambient temperature with and without wind. Eur. J. Appl. Physiol. 78 (6), 487e493. PMID: 9840402. McArdle, W., Katch, F., Katch, V., 2007. Exercise Physiology: Energy, Nutrition and Human Performance. Lippincott Williams & Wilkins. Morgan, W., Borg, G.A., 1976. Perception of effort in the prescription of physical activity. In: Nelson, T. (Ed.), Mental Health and Emotional Aspects of Sports. Chicago, IL, pp. 126e129. Periard, J.D., Cramer, M.N., Chapman, P.G., Caillaud, C., Thompson, M.W., 2011. Cardiovascular strain impairs prolonged self-paced exercise in the heat. Exp. Physiol. 96 (2), 134e144. PMID: 20851861. Ramanathan, N.L., 1964. A new weighting system for mean surface temperature of the human body. J. Appl. Physiol. 19 (3), 531e533. PMID: 14173555. Satsumoto, Y., Murayama, C., Takeuchi, M., 2009. Effect of moisture sorption of underwear material on clothing microclimate in a hot environment. Heat. Trans. Asian Res. 38 (1), 1e14. http://dx.doi.org/10.1002/htj.20220. Sawka, M.N., Wenger, C.B., Pandolf, K.B., 2011. Thermoregulatory responses to acute exercise-heat stress and heat acclimation. Compr. Physiol., 157e185. http:// dx.doi.org/10.1002/cphy.cp040109. Sparling, P.B., Snow, T.K., Millard-Stafford, M.L., 1993. Monitoring core temperature during exercise: ingestible sensor vs. rectal thermistor. Aviat. Space Environ. Med. 64 (8), 760e763. PMID: 8368992. Toner, M.M., Sawka, M.N., Foley, M.E., Pandolf, K.B., 1986. Effects of body mass morphology on thermal responses in water. J. Appl. Physiol. 60 (2), 521e525. PMID: 3949658. Wendt, D., van Loon, J.C., van Marken Lichtenbelt, Wouter D., 2007. Thermoregulation during exercise in the heat. Sports. Med. 37 (8), 669e682. Woodcock, A.H., 1962. Moisture transfer in textile systems. Text. Res. J. 32 (8), 628e 633. PMID: 17645370. Zhang, P., Gong, R.H., Yanai, Y., Tokura, H., 2002. Effects of clothing material on thermoregulation responses. Text. Res. J. 72 (1), 83e89.
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Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo
The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat Justin De Sousa*, Christopher Cheatham, Matthew Wittbrodt 1 Western Michigan University, 1903 W. Michigan Ave, Kalamazoo, MI 49008, USA
a r t i c l e i n f o
a b s t r a c t
Article history: Received 27 October 2013 Accepted 6 April 2014 Available online xxx
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% VO2peak) 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. Ó 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Keywords: Clothing Heat Exercise
1. Introduction Strenuous exercise in combination with environmental heat stress significantly impacts fatigue, diminishing exercise performance (Gisolf and Wenger, 1984; Gonzalez-Alonso et al., 1999; Hargreaves, 2008; Sawka et al., 2011) and increasing the risk of heat-related injury (Gonzalez-Alonso et al., 1999; Hargreaves, 2008; Periard et al., 2011). Increased cardiovascular strain resulting from hyperthermia reduces maximal cardiac output (Cheuvront et al., 2010; Gonzalez-Alonso et al., 2008; Hargreaves, 2008), mean arterial pressure (Gonzalez-Alonso and Calbet, 2003; Hargreaves, 2008), oxygen delivery (Fink et al., 1975; Gonzalez-Alonso et al., 2008), overall oxygen uptake (Cheuvront et al., 2010; Fink et al., 1975; Gonzalez-Alonso and Calbet, 2003; Periard et al., 2011) and central neuromuscular drive (Cheung and Sleivert, 2004). Therefore, optimizing tolerance in the heat through attenuating heat stress by balancing metabolic heat gain with heat loss becomes a central focus in maintaining performance and safety (Cheuvront et al., 2010). One distinct method utilized in an attempt to mitigate heat stress and improve heat tolerance is the employment of clothing with properties that positively augment heat dissipation
* Corresponding author. Tel.: þ1 269 365 8509. E-mail addresses: [email protected] (J. De Sousa), chris.cheatham@ wmich.edu (C. Cheatham), [email protected] (M. Wittbrodt). 1 Georgia Institute of Technology, 225 North Ave NW, Atlanta, GA 30332, USA.
from the exercising body to the external environment (Wendt et al., 2007). The design and fabric are principal factors that influence a garment’s insulation and air permeability properties, which subsequently affect heat transfer (Woodcock, 1962). The use of clothing provides a layer of insulation and a barrier between the skin and the environment (Gavin, 2003). Wool and cotton garments have high sorption properties, causing the fabric to hold sweat, which may lead to decreased comfort and impaired heat dissipation as a result of decreased evaporation of sweat (Dai et al., 2008). Conversely, synthetic polyester garments have been suggested to improve sweat evaporation, due to increased fabric permeability, possibly leading to a lower core temperature (Gavin et al., 2001; Woodcock, 1962). Athletes have utilized clothing from athletic apparel companies who market the garments’ effects on limiting heat stress by keeping the athlete cool and dry, citing improved ventilation and evaporative characteristics. However, whether these synthetic polyester garments have a significant effect on the physiological and perceptual responses during exercise in the heat still remains unclear and current research has demonstrated inconclusive evidence. A study by Gavin et al. (2001) revealed no alterations in physiological or perceptual responses during exercise of eight highly trained athletes in a warm environment with clothing conditions consisting of a short sleeved cotton and synthetic polyester shirt. The researchers suggested that the exercise intensity of 70% VO2peak
http://dx.doi.org/10.1016/j.apergo.2014.04.006 0003-6870/Ó 2014 Elsevier Ltd and The Ergonomics Society. All rights reserved.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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for 30 min may not have been significant enough to stress the highly trained participants. As a result, the exercise intensity and duration may have failed to adequately stress the participants’ thermoregulatory systems, negating any impact of clothing. In a follow-up study utilizing similar environmental and clothing conditions, Brazaitis et al. (2010) found that higher exercise intensities revealed better sweat evaporation and reduced sweat sorption in participants wearing the polyester garments. However, no differences in the two garments for any thermo-physiological or subjective comfort responses were observed. While Gavin et al. (2001) reported that their study may have been limited by an exercise intensity and duration that was too low in relation to the training level of their participants, Brazaitis et al. (2010) did not measure the aerobic capacity of their participants. This would make it difficult to assess whether the assigned absolute workload was an intense level of physical activity for all eight participants. Therefore the absolute treadmill workload of 5 mph at 1% grade may have fell short of their desired intensity range. Even with each participant performing three 20-min bouts of exercise with five minutes of rest, the physiological stress of the exercise intensity would be different for each participant and highly dependent on their aerobic capacity. This would make it problematic to elucidate clothing’s impact on thermoregulation at a specific intensity of exercise. For this reason, quantifying the stress relative to an individual’s physiological system would better establish equivalent exercise intensities among participants (McArdle et al., 2007). Therefore, the aim of the present is to 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 moderate intensity exercise in the heat. To the best of our knowledge, no study has explored this in recreationally active participants using a prolonged, continuous exercise protocol that establishes exercise intensity as a percent of their current aerobic capacity. 2. Material and methods 2.1. Participants Ten recreationally active male participants (Age: 24.5 3.5 yrs, Height: 179.8 0.1 cm, VO2peak: 42.4 6 mL kg1 min1, Body Weight: 90.8 13.1 kg, Body Mass Index: 27.9 3.8 kg m2, Body Fat: 15.4 6.0%) participated in this study. All participants were healthy, free of disease and medication use, not obese (Body Mass Index < 30.0 kg m2), and non-smokers. The study was approved by the Human Participants Institutional Review Board at Western Michigan University. All participants read and signed the informed consent prior to participation in the study. 2.2. Research design Each participant visited the human performance research laboratory on three separate occasions. During the first visit, anthropometric measurements were obtained and each participant performed a maximal graded exercise test on a cycle ergometer. On the second and third visits, a heat stress test was performed. One heat stress test was conducted with the participant wearing a nonform fitted, 100% cotton, short sleeved t-shirt (COT) and the other heat stress test was conducted with the participant wearing a short sleeved, form fitted, commercially available, synthetic shirt (81% polyester and 19% elastane) (SYN). The SYN shirt was promoted by the manufacturer to be moisture wicking and have enhanced air permeability due to a ventilated mesh back. The COT and SYN shirts were fitted to cover the same skin surface area and each participant
wore the same athletic shoes, ankle socks and knee length shorts (top of the patella) during both heat stress tests. The order of the heat stress tests was counter-balanced and each participant finished the study in a four week time period. Prior to each visit, participants were instructed to refrain from alcohol, caffeine, and physical activity the day before and the day of the visits to the laboratory. 2.2.1. Anthropometric assessment and graded exercise test Upon arrival to the laboratory on the first day, all research procedures were explained to the participants and informed consent was obtained. Each participant then completed a health history questionnaire in order to confirm that they were healthy, free of disease and medication use, and classified as “low-risk” according to the American College of Sports Medicine (ACSM) guidelines (2010). Each participant then had their anthropometric measurements assessed. Weight and height were measured via a digital scale (Totalcomp, Fair Lawn, NJ) and stadiometer (Seca Instruments Ltd, Hamburg, Germany), respectively. Skinfold thickness was measured at seven sites (triceps, abdomen, thigh, calf, suprailiac, chest, subscapular) using skinfold calipers (Lange, Beta Technology Inc. Cambridge, MD). Each site was measured three times with the mean of the three measurements used as the skinfold thickness. The Jackson & Pollock 7-site equation was used to calculate body density from the skinfold assessment and the Brozek equation was used to calculate percent body fat from body density (Brozek et al., 1963; Jackson and Pollock, 1985). Upon completion of the anthropometric assessment, the participant completed a graded exercise test on a cycle ergometer (Corival, Lode B.V., Groningen, Netherlands) to determine VO2peak. Prior to all tests, the metabolic cart was calibrated using a 3-L syringe and gases of known concentration. Each participant was then fitted with a nose clip and a mouthpiece for the collection of expired respiratory gases using the metabolic measurement cart (TrueOne 2400, ParvoMedics, Sandy, UT) and a telemetry heart rate (HR) monitor (Polar USA, Lake Success, Long Island, NY). Lastly, each participant was instructed on using the Borg Ratings of Perceived Exertion (RPE) chart (Morgan and Borg, 1976). Once instrumentation of the participant was complete, the exercise test began. The graded exercise test started at 60 Watts for 2 min and then exercise intensity was increased 20 W every minute until volitional fatigue. VO2peak was defined as the greatest 30-sec average during the test. 2.2.2. Heat stress tests During the second and third visits to the laboratory, each participant completed a heat stress test (COT or SYN). To ensure hydration, each participant was instructed to consume w6e8 mL of water per kilogram of body weight 2 h prior to testing. Upon arrival to the laboratory, each participant was instructed to void and nude body weight was measured. Each participant was then instructed to insert a rectal temperature probe (Physitemp Instruments Inc., Clifton, NJ) 13 cm past the anal sphincter. After insertion of the rectal probe, skin thermocouples (Physitemp Instruments Inc., Clifton, NJ) were attached to the right side of the body at the chest, triceps, thigh and calf with waterproof tape (Hytape, Hytape International Inc., Patterson, NY) for determination of mean skin temperature (MTsk) (Ramanathan, 1964). It is important to note that the chest and triceps skin thermocouples were covered by the shirt in both conditions. Rectal and skin thermocouples were interfaced to a data acquisition system (Thermes USB, Physitemp Instruments Inc., Clifton, NJ), which was linked to a PC computer. For the determination of sweat volumes an automated resistance hygrometry system (QSweat, WR Medical Electronics Co.,
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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Stillwater, MN) was utilized (Bullard, 1962). Ventilated capsules (0.787 sq cm) were secured with rubber straps to the upper chest, back, thigh, and forearm and then interfaced to a PC for the continuous collection of sweat volume. A telemetry HR monitor was strapped around the participant’s chest for the measurement of HR. Lastly, the participant’s shirt was weighed (LC101, Omega Engineering Inc., Stamford, CT) and then placed on the individual before they were seated on a lounge chair in a semi-recumbent position. Once instrumentation of the participant was completed, the participant sat quietly for 20 min in a thermo-neutral environment (24 C, 60% RH) (24 CBASE), followed by 30 min of seated rest in a heated environment (33 C, 60% RH) (33 CBASE). Rectal temperature (Tre), skin temperatures and sweat rate (SR) were measured continuously. Thermal sensation (Gagge et al., 1967), sweating sensation (Gavin et al., 2001), RPE and HR were assessed during the last minute of 24 CBASE and 33 CBASE. After completion of 33 CBASE, the participant was transported to the electronically braked cycle ergometer and began the exercise portion of the trial. Exercise consisted of cycling for 45 min at 50% VO2peak in 33 C air and 60% RH (33 CEX). Expired respiratory gases were assessed during 0e15 min, 25e30 min and 40e45 min of exercise. During minutes 5e7 of exercise, if the participant was not within 5% of the desired 50% VO2peak, workload adjustments were made to elicit the desired exercise intensity. This workload was then replicated during the participant’s second trial. Rectal temperature, skin temperatures and SR were measured continuously during exercise. HR, RPE, thermal sensation, and sweat sensation were recorded every 5 min. Water intake was monitored and measured. Each participant was permitted to consume water ad libitum during the first heat stress test. To control for hydration status between the two heat stress test fluid consumption during session two mimicked the initial heat stress test. At the completion of each heat test, the participant’s garment was immediately placed in the same freezer bag, sealed and weighed. All probes and capsules were removed and the participant was instructed to towel off and weigh them self nude.
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To analyze the difference between the COT and SYN apparel shirts for shirt weight and whole-body sweat volume and rate, a paired samples t-test was used. The level of statistical significance was established a priori as P < 0.05. The SPSS statistical package (v17.0) was used for data analysis. Data is presented as means (M) standard deviations (SD). 3. Results 3.1. Physiological variables 3.1.1. Exercise intensity There was no significant difference in workload between the clothing conditions (P ¼ 0.989). Mean exercise intensity (L min1) was 1.90 0.29 (50.2 3.4 %VO2Peak) in the COT clothing condition and 1.88 0.40 (50.1 1.6 %VO2Peak) in the SYN clothing condition. 3.1.2. Rectal temperature The response in Tre over time during the COT and SYN clothing conditions is displayed in Fig. 1. As expected, there was a significant main effect for time (P < 0.001) in that there was a progressive increase from 33 CBASE to the end of 33 CEX. Overall, there was no significant difference between the clothing conditions (COT: 37.54 0.34, SYN: 37.42 0.27 C; P ¼ 0.065), although the clothing-by-time interaction was significant (P ¼ 0.001). Post-hoc testing revealed that Tre was greater during COT compared to SYN during the last 15 min of exercise. 3.1.3. Skin temperature The response in MTsk over time in the COT and SYN clothing conditions is demonstrated in Fig. 2. Similar to the results reported above for Tre, there was a significant main effect for time (P < 0.001) with MTsk progressively increasing with the duration of the trial. Overall, there was no significant difference between the clothing conditions (COT: 35.77 1.13, SYN: 35.83 0.90 C; P ¼ 0.762) and
2.3. Calculations 2.3.1. Mean skin temperature MTsk was calculated using the weighting formula: MTsk ( C) ¼ (0.28 * Tchest) þ (0.08 * Ttricep) þ (0.28 þ Tthigh) þ (0.22 * Tcalf) þ (0.14 * Tforearm) (Toner et al., 1986). 2.3.2. Sweat volumes, whole body sweat loss and shirt weight Cumulative sweat volume was calculated as the sum of sweat produced in mL cm2 during 24 CBASE, 33 CBASE and 33 CEX. Whole body sweat loss was calculated as the difference between pre and post body weight, plus the amount of fluid consumed during the trial. Shirt weight difference was calculated as the difference between shirt weight pre and post exercise. 2.4. Statistical analysis To analyze the differences between the COT and SYN apparel shirts for temperature, sweat volume and rate, HR and perceptual data, a two-way analysis of variance (ANOVA) with repeated measures was utilized. The factors in the analysis were clothing (COT vs. SYN) and time with both being repeated measures. In the case of a significant main effect for time or interaction, post-hoc tests were performed using a simple effects analysis with the Bonferroni adjustment.
Fig. 1. The response in rectal temperature during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions at all times points, p < 0.001. No significant differences between conditions, p ¼ 0.065. *, Indicates a significant difference in the clothing-by-time interaction between COT and SYN, p < 0.05.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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difference between the clothing conditions (COT: 124 5, SYN: 119 5 beats min1; P ¼ 0.127). As expected, there was a significant main effect for time (P < 0.001). The clothing by time interaction was not significant (P ¼ 0.370). 3.2. Perceptual variables 3.2.1. Thermal sensation Fig. 5 displays the response in thermal sensation over time in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions (COT: 5.8 1.0, SYN: 5.6 0.9; P ¼ 0.320). As expected, there was a significant main effect for time (P < 0.001). Post-hoc testing revealed a significant difference in 24 CBASE vs. 33 CBASE and all exercise time points and 33 CBASE vs. all exercise time points. The clothing by time interaction was not significant (P ¼ 0.990).
Fig. 2. The mean skin temperature response during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions at all times points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothingby-time interaction, p > 0.05.
the clothing-by-time interaction (P ¼ 0.165). However, it is important to indicate that the clothing-by-time interaction was significant for skin temperature at the chest (P ¼ 0.001). Post-hoc testing revealed that Tchest was greater during COT compared to SYN at 25, 40, and 45 min exercise. 3.1.4. Cumulative sweat volume Fig. 3 displays the response in cumulative sweat volume in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions with respect to cumulative sweat volume at the chest (COT: 50.02 15.11, SYN: 43.13 15.25 mL cm2; P ¼ 0.120), back (COT: 53.37 20.33, SYN: 52.1 26.68 mL cm2; P ¼ 0.843), thigh (COT: 31.77 12.07, SYN: 33.04 12.07 mL cm2; P ¼ 0.934) and forearm (COT: 35.58 17.79, SYN: 35.58 17.80 mL cm2; P ¼ 0.562). As expected, there was a significant main effect for time for cumulative sweat volume (P < 0.001) at the chest, back, thigh and forearm. Post-hoc testing revealed that all time points for chest, back, thigh and forearm were significantly different from each other. The clothing-by-time interaction was not significant for cumulative sweat volume at the chest (P ¼ 0.076), back (P ¼ 0.947), forearm (P ¼ 0.730) and thigh (P ¼ 0.992).
3.2.2. Sweat sensation Fig. 6 displays the response in sweat sensation over time in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions (COT: 3.5 1.4, SYN: 3.5 1.4; P ¼ 0.702). As expected, there was a significant main effect for time (P < 0.001). Post-hoc testing revealed a significant difference in 24 CBASE vs. 33 CBASE and all exercise time points and 33 CBASE vs. all exercise time points. The clothing by time interaction was not significant (P ¼ 0.876). 3.2.3. Perceived exertion Fig. 7 displays the response in perceived exertion over time in the COT and SYN clothing conditions. Overall, there was no significant difference between the clothing conditions (COT: 10.1 2.9, SYN: 9.8 2.8; P ¼ 0.400). As expected, there was a significant main effect for time (P < 0.001). Post-hoc testing revealed a significant difference in 24 CBASE vs. 33 CBASE and all exercise time points and 33 CBASE vs. all exercise time points. The clothing by time interaction was not significant (P ¼ 0.655).
3.1.5. Whole body sweat loss and changes in shirt weight The response in whole body sweat loss over time in conjunction with body weight and shirt weight difference pre-24 CBASE to post-33 CEX in COT and SYN is displayed in Table 1. Overall, there was no significant difference between the clothing conditions with respect to whole body sweat loss (P ¼ 0.396) and body weight differences pre-24 CBASE to post-33 CEX (P ¼ 0.152). However, there was a significant difference in shirt weight (P ¼ 0.05) between pre-24 CBASE and post-33 CEX. 3.1.6. Heart rate The response in HR over time in the COT and SYN clothing conditions is displayed in Fig. 4. Overall, there was no significant
Fig. 3. The cumulative sweat volume during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions at the chest, back, thigh and forearm, p < 0.001. Significant differences at the chest, back, thigh and forearm during both conditions, p < 0.05. No significant difference in the clothing-by-time interaction at the chest, back, thigh and forearm, p > 0.05.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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Table 1 Body weight/shirt weight difference and total body sweat loss during heat stress tests.
Whole body sweat loss (mL) Pre and post BW difference (g) Shirt weight difference (g)
COT
SYN
1284.6 120.1 1028.0 383.1 123.6 14.0
1182.6 89.4 826 305.6 100.6 8.9a
Note: Whole body sweat loss was calculated as the difference between pre- and post-body weight, plus the amount of fluid consumed during the trial. a denotes significant differences between SYN and COT conditions.
4. Discussion This study aimed to investigate the effects that a form fitted, moisture-wicking fabric shirt, promoted to have improved evaporative and ventilation properties, has on the thermoregulatory, physiological and perceptual responses during moderate intensity exercise in the heat. An exercise protocol of 50% VO2peak for 45 min in environmental conditions of 33 C/60% RH was selected in order to impose a heat load significant enough to stress the thermoregulatory system of the recreationally active participants and to simulate conditions often imposed on an individual while aerobically training in the summer. Furthermore, the protocol was utilized to produce a sufficient heat load where the moisturewicking fabric shirt may prove beneficial in the maintenance of body temperature and performance without providing a metabolic load so severe that fatigue sets in too early, not stressing the thermoregulatory system adequately (Gavin et al., 2001). The most interesting finding in the present study is that during the last 15 min of exercise Tre was significantly lower in SYN compared to COT. This is inconsistent with previous research investigating garment effects on Tre during exercise in similar environments (Brazaitis et al., 2010; Gavin et al., 2001). Gavin et al. (2001) reported no significant difference in Tre when examining the difference between polyester and cotton garments (shortsleeved t-shirts, shorts and socks) on thermoregulation during
Fig. 4. The heart rate response during the heat stress tests. Values are displayed as means SD. Main effect for time in both conditions, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
Fig. 5. The thermal sensation during the heat stress tests. Values are displayed as means SD. Main effect for time between 24 CBASE and 33 CBASE, 24 CBASE and all exercise time points and 33 CBASE and all exercise time points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
exercise in 30 C and 35% RH air. Gavin et al. (2001) utilized an intensity of 70% VO2peak for 30 min in highly trained aerobic athletes (VO2peak of 67.5 1.4 mL kg1 min1), which may not have produced a significant enough stress in relation to participant training status. Similarly, Brazaitis et al. (2010) found no significant
Fig. 6. The sweat sensation during the heat stress tests. Values are displayed as means SD. Main effect for time between 24 CBASE and 33 CBASE, 24 CBASE and all exercise time points and 33 CBASE and all exercise time points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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Fig. 7. The perceived exertion during the heat stress tests. Values are displayed as means SD. Main effect for time between 24 CBASE and 33 CBASE, 24 CBASE and all exercise time points and 33 CBASE and all exercise time points, p < 0.001. No significant differences between conditions, p > 0.05 and in the clothing-by-time interaction, p > 0.05.
difference in Tre, while evaluating the effects that two kinds of longsleeved t-shirts (94% cotton/6% elastane; 93% polyester/7% elastane) have on the thermoregulatory response during exercise (8 km/h at 1 grade on a treadmill) in a warm and humid environment (25 C and 60% RH). In the present study, a mesh back in the SYN condition, but not in the COT condition, may have resulted in greater ventilation due to higher air permeability, contributing to the observed differences in Tre. The polyester garments in both the Brazaitis et al. (2010) and Gavin (2003) studies were not reported to have a ventilated mesh back, possibly explaining why no difference in Tre was found. Zhang et al. (2002) demonstrated that clothing with high air permeability resulted in significantly lower Tre during exercise in the heat with wind, but not without wind. Likewise, Brownlie et al. (1987) found that clothing with limited vapor permeability caused a significant increase in Tre during exercise in the heat with wind. In the present study wind was not utilized, although it can be inferred that the use of wind would further reduce Tre in the SYN condition because of its superior permeability properties. Clothing with increased air permeability will increase heat loss via convection as the wind carries away warm air surrounding the body (Zhang et al., 2002; Bouskill et al., 2002). Increases in air movement by wind or the movement of the body will facilitate heat dissipation in both conditions, but an even greater affect would result in the SYN condition due to its superior permeability. The COT fabric’s higher absorption and reduced permeability creates a thicker ‘still air barrier’ between the skin and the environment (Woodcock, 1962). This could lead to decreases in dry heat transfer and a possible rationale for an increase in Tre. There was no significant difference in cumulative sweat volume at the chest, back, forearm and thigh, suggesting that clothing of different fabric and characteristics may not affect sweat loss. This is in contrast to Ha et al. (1999), who found that fabrics with high air permeability and moisture regain had lower sweat rates during intermittent exercise (30% VO2peak) at 27 C. Similarly, Kwon et al. (1998) reported greater sweat rates in participants wearing a
long-sleeve 100% polyester shirt compared to a long sleeved 100% cotton shirt during intermittent exercise at 40% VO2peak in 30 C. The intermittent nature of the exercise combined with moisture regain properties of the fabric may be credited for the differences in sweat rate observed in the previously mentioned studies and the present one. Cotton fabrics have high sorption properties (Dai et al., 2008); therefore during periods of rest, the increased wetness of the cotton fabric may have cooled the skin and decreased overall sweat rate. Thermal conductivity has been shown to increase in clothes with high regain properties. This would result in a decrease in the temperature within the clothing microclimate and possible chilling of the participant (Satsumoto et al., 2009). Brazaitis et al. (2010) found that during post-exercise recovery MTsk tended to decline to lower than pre-exercise levels in participants wearing cotton shirts compared to polyester ones, revealing the ability of clothing with high regain properties to cool the skin in a rested state. The use of a continuous protocol in the present study would have assuaged the conductive heat loss from a cool and saturated garment on the skin, possibly increasing reliance on the evaporation of sweat for heat dissipation. Furthermore, Ha et al. (1999) postulated that a lower sweat rate may be due to the combined effects of moisture regain and air permeability, which may be acceptable, since the present study reveals that these properties have no effect on sweat rate independent of each other. The cotton shirt retained a significantly greater amount of sweat than the SYN shirt. This exhibits the high sorption property of the cotton fabric and increased ability of the SYN to promote greater evaporation of sweat. These findings agree with other studies utilizing similar protocols and environmental conditions (Gavin et al., 2001; Brazaitis et al., 2010). Gavin et al. (2001) and Brazaitis et al. (2010) both demonstrated properties of less sweat sorption in the polyester condition with no impact on temperature regulation during exercise in the heat. The increased moisture-wicking ability of the SYN condition did not subsequently alter body weight loss as no significant difference was observed, further reinforcing the notion that the reduced weight of the SYN shirt was due to its greater evaporative characteristics. An increase in exercise duration may prove beneficial to future research. In the present study, as exercise duration progressed there was a main effect between COT and SYN with respect to Tre. It is possible that the evaporative fabric plays a larger role in the maintenance of core temperature during prolonged exercise in the heat (>45 min). The relationship between increasing core temperature and decreasing exercise capacity has been demonstrated in previous research (Galloway and Maughton, 1997). If the observed trend continued past 45 min of exercise, the SYN garment may prove beneficial in reducing the possibility of heat related illness and in the maintenance of aerobic performance during prolonged exercise in the heat. The ability of the SYN to retain less moisture and evaporate sweat more efficiently may reduce the overall heat load on the body by being less of a barrier and allowing for greater heat dissipation to the environment. It should also be noted that rectal temperature has been shown to lag behind core temperature (Sparling et al., 1993). Therefore, similarities in Tre between conditions may have resulted, if exercise progressed beyond 45 min. In both conditions HR quickly increased within the first five minutes of exercise before leveling off with gradual increases until the cessation of exercise. Overall, there was no significant difference between clothing conditions, possibly due to the equivalent amount of participant fluid loss and comparable exercise intensity. Therefore, despite a difference in garment fabric and properties a uniform cardiovascular stress was observed between trials. These findings are similar to Gavin et al. (2001), who found no significant difference in HR between cotton and polyester garments during exercise in the heat. Conversely, Ha et al. (1995) found that
Please cite this article in press as: De Sousa, J., et al., The effects of a moisture-wicking fabric shirt on the physiological and perceptual responses during acute exercise in the heat, Applied Ergonomics (2014), http://dx.doi.org/10.1016/j.apergo.2014.04.006
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participants wearing polyester garments had a higher HR than those wearing cotton garments during intermittent exercise (30% VO2peak) at 27 C. The researchers cited reduced thermal insulation due to absorption of moisture by the cotton fabric as the cause for accelerated heat loss and lower HR. However, the increase in moisture absorption because of high regain properties in the cotton garment would allow for delayed evaporative cooling during the recovery phase. This was not observed in the Gavin et al. (2001) and present studies, which employed continuous exercise. Interestingly, and contrary to Ha et al. (1995), Brazaitis et al. (2010) did not observe any difference in HR between conditions during intermittent exercise or during 60 min of seated recovery. Exercise in the heat at a constant intensity is associated with an increase in RPE as duration progresses (Gonzalez-Alonso et al., 1999). Both the COT and SYN conditions followed similar trends of steadily increasing with exercise duration. However, no significant difference in RPE was attributed to the type of garment worn. Similarly, perception of skin wetness and thermal comfort did not differ with respect to both conditions. Even though the COT fabric absorbed more moisture and weighed more than the SYN, it did not alter the participant’s perception to thermal comfort, sweat sensation or perceived exertion. This agrees with Gavin et al. (2001) and Brazaitis et al. (2010), who found no differences in thermal comfort and sweat sensation between exercise ensembles at any time point, despite the cotton shirt absorbing significantly more sweat from pre to post exercise. It appears that the sorption properties and type of garment fabric plays no role in the perception of thermal comfort, sweat sensation and exertion during exercise in the heat. In conclusion, the form fitted, moisture-wicking fabric shirt, promoted to have improved evaporative and ventilation properties produced a significantly lower Tre during the last 15 min of exercise when compared to a cotton garment. The synthetic polyester shirt exhibited superior evaporative characteristics and lower regain qualities. Moreover, as exercise duration increases, the SYN shirt may prove beneficial in the preservation of body temperature, thus reducing the likelihood of heat related illness and maintaining exercise performance in the heat.
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