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Comparison of Body Cooling Methods on Physiological and Perceptual Measures of Mildly Hyperthermic Athletes

DeMartini, Julie K1; Ranalli, Gregory F1; Casa, Douglas J1; Lopez, Rebecca M2; Ganio, Matthew S3; Stearns, Rebecca L1; McDermott, Brendon P4; Armstrong, Lawrence E1; Maresh, Carl M1

The Journal of Strength & Conditioning Research: August 2011 - Volume 25 - Issue 8 - p 2065-2074
doi: 10.1519/JSC.0b013e3182259b1d
Original Research

DeMartini, JK, Ranalli, GF, Casa, DJ, Lopez, RM, Ganio, MS, Stearns, RL, McDermott, BP, Armstrong, LE, and Maresh, CM. Comparison of body cooling methods on physiological and perceptual measures of mildly hyperthermic athletes. J Strength Cond Res 25(8): 2065-2074, 2011—Hyperthermia is common among athletes and in a variety of environments. The purpose of this study was to evaluate the effectiveness of cooling methods on core body temperature, heart rate (HR), and perceptual readings in individuals after exercise. Sixteen subjects (age: 24 ± 6 years, height: 182 ± 7 cm, weight: 74.03 ± 9.17 kg, and body fat: 17.08 ± 6.23%) completed 10 exercise sessions in warm conditions (WBGT: 26.64 ± 4.71°C) followed by body cooling by 10 different methods. Cooling methods included cold water immersion (CWI), shade, Port-a-Cool® (FAN), Emergency Cold Containment System® (ECCS), Rehab. Hood® (HOOD), Game Ready Active Cooling Vest™ (GRV), Nike Ice Vest™ (NIV), ice buckets (IBs), and ice towels (IT). These cooling modes were compared with a control (SUN). Rectal temperature (T re), HR, thermal sensation, thirst sensation, and a 56-question Environmental Symptoms Questionnaire (ESQ) were used to assess physiological and perceptual data. Average T re after exercise across all trials was 38.73 ± 0.12°C. After 10 minutes of cooling, CWI (−0.65 ± 0.29°C), ECCS (−0.68 ± 0.24°C), and IB (−0.74 ± 0.34°C) had significantly (p < 0.006) greater decreases in T re compared with that in SUN (−0.42 ± 0.15°C). The HR after 10 minutes of cooling was significantly (p < 0.006) lower for CWI (82 ± 15 b·min−1), ECCS (87 ± 14 b·min−1), and IT (84 ± 15 b·min−1) when compared with SUN (101 ± 15 b·min−1). The thermal sensation between modalities was all significantly (p < 0.006) lower (CWI: 1.5 ± 0.5; Fan: 3.0 ± 1.0; ECCS: 4.5 ± 1.0; Hood: 4.5 ± 0.5; GRV: 4.0 ± 0.5; NIV: 4.5 ± 1.0; IB: 4.0 ± 1.0; IT: 3.0 ± 1.0) when compared with SUN (5.5 ± 0.5), except for Shade (5.0 ± 1.0). There were no significant differences (p > 0.006) in thirst sensation between modalities. The ESQ scores were significantly (p < 0.006) lower for CWI (1 ± 6), Fan (4 ± 5), and IT (3 ± 8) compared with that for SUN (13 ± 12). In conclusion, when athletes experience mild hyperthermia, CWI, ECCS, and IB resulted in a significantly greater decrease in T re. These cooling strategies are recommended to decrease T re during a brief recovery period between exercise bouts.

1Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, Connecticut; 2Department of Orthopedics and Sports Medicine, University of South Florida, Tampa, Florida; 3Department of Health Science, Kinesiology, Recreation and Dance, University of Arkansas, Fayetteville, Arkansas; and 4Department of Health and Human Performance, University of Tennessee at Chattanooga, Chattanooga, Tennessee

Address correspondence to Julie K. DeMartini,

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Exercise, and especially exercise in the heat, results in an increase in core body temperature (hyperthermia). Hyperthermia is common in the athletic population, and severe hyperthermia (>104°C) can result in dangerous and potentially life threatening situations (7,8,10,14,26). There are currently 2 prevailing theories on how hyperthermia will impact the exercising athlete. The first theory states that if an athlete reaches a critical limiting temperature (consistently ca. 40°C, 104°F) during exercise, this temperature causes fatigue and prematurely ends exercise (18,19). However, a recent study by Ely et al. (17) proposed that those results favoring a critical limiting temperature were in fact attributed to multiple physiological factors (high skin temperature, high cardiovascular strain, etc.) and did not solely rely on an absolute body temperature. The second theory states that the athlete's brain anticipates reaching this critical limiting temperature, and alters exercise intensity to avoid reaching such a temperature, thus allowing the athlete to continue exercising, albeit at a lower intensity (25,37,38).

It is necessary to investigate the physiological benefit of body cooling a hyperthermic athlete. Body cooling an athlete who has been, or who will be, exercising in the heat would have a beneficial effect on the physiological variables associated with the aforementioned theories. Although it is well documented that rapid cooling via ice water immersion (CWI) should immediately be initiated in cases of exertional heat stroke (EHS [3,6,9,10]), literature is lacking in the area of body cooling for nonemergency situations such as recovery during a brief break in exercise.

In addition to cooling for the purpose of treating EHS, other areas of interest include precooling an athlete to prevent potentially dangerous hyperthermia from occurring, and cooling athletes between bouts of exercise (such as a halftime) to improve performance for subsequent bouts of exercise. Cooling an athlete before exercise or during a break in exercise has been shown to result in performance and physiological benefits in athletic competition (31). Improved performance is attributed to an improved thermoregulatory and cardiovascular state, which may result from body cooling.

The practice of body cooling for performance enhancement is relatively new to athletics. Although CWI is considered the most efficient means of body cooling, it may not always be the best option in non-EHS situations (31,43). In these nonemergency situations, practicality must also be considered in addition to fast cooling rates. For example, during a halftime of a football game, it would not be practical for athletes to immerse themselves in a cold water bath because of uniform and equipment restraints. Moreover, examination of different cooling modalities has been addressed by several body cooling studies (15,31); however, these studies independently report varying results and typically implement only a single cooling modality. Therefore, the most effective methods are yet to be determined. Moreover, valid recommendations for athletes cannot be made because of conflicting findings. It is imperative to determine which cooling modalities are the most effective (decreasing core body temperature) and practical (comfort for the athlete, convenience, etc.) for athletes.

Therefore, the purpose of this study was to evaluate the effectiveness of 9 body cooling methods, compared with a control, on rectal temperature (Tre), heart rate (HR), and perceptual measurements of individuals after exercise in the heat. It was hypothesized that cold water immersion (CWI) would provide the greatest decrease in core body temperature, because this response is consistent in the body cooling literature.

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Experimental Approach to the Problem

To our knowledge, many of the cooling modalities that were evaluated in this protocol have not previously been studied. In addition, previous studies fail to implement an extensive randomized crossover design to simultaneously evaluate such a wide variety of cooling modalities. Furthermore, we intend to provide direction for certified athletic trainers and other medical personnel as to which cooling modalities can be considered for athletes during a brief break in exercise, as an alternative to using no cooling modality.

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Sixteen subjects, 9 male and 7 female (19-39 years old [mean ± SD] age: 24 ± 6 years; height: 182 ± 7 cm; weight: 74.03 ± 9.17 kg; body fat: 17.08 ± 6.23%) were recruited from the University campus and the local community. Screening information was obtained to ensure that the subjects met the following criteria: (a) had no known chronic health problems, (b) exercised a minimum of 30 minutes thrice a week, (c) had no previous history of heat illness in the past 3 years, (d) had no history of cardiovascular, metabolic, or respiratory disease, (e) were not febrile, (f) were not currently taking any supplements or drugs that influence thermoregulation. The subjects were instructed to refrain from intense physical activity during data collection.

The subjects attended a briefing meeting and signed an informed consent document before experimentation to ensure the understanding of the testing parameters and the risks and benefits associated with the study. All the subjects completed medical history questionnaires. The study protocol was approved by the University's Institutional Review Board.

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Experimental Protocol


On day 1, height and body fat measures (Lange Skinfold Calliper; Beta Technology Inc., Houston, TX, USA) were taken for all the subjects (3 site computation, Jackson-Pollock equation). On the morning of each experimental trial, the subjects reported in a euhydrated state to an outdoor pavilion at the testing site. The subjects were asked to provide a urine sample, and hydration status was confirmed via urine color (4). The subjects were fitted with an HR monitor (Polar Electro Inc., Lake Success, NY, USA), which was worn during exercise so that the HR could be monitored by the subject. Body weight (determined using equipment from Tanita Corp., Tokyo, Japan) and HR were recorded for each subject. Thermal sensations were reported using a 9-point (0 = “unbearably cold,” 8 = “unbearably hot”) thermal sensation scale (39) with instruction given as “how hot or cold are you right now” and thirst sensations were reported using a 9-point (1 = “not thirsty at all,” 9 = “very, very thirsty”) thirst scale (32) with instruction given as “how thirsty are you right now.” After these measurements, all the subjects completed a 56-question environmental symptoms questionnaire (ESQ) (33) before the first bout of exercise. The ESQ is a list of 56 questions that addresses the presence of signs and symptoms. Responses are noted via a Likert scale (0 = “not at all,” 5 = “extremely”) to indicate the extent to which signs and symptoms are being experienced.

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Exercise Bouts

Ten experimental trials were conducted for each subject across 4 days. The subjects exercised for 45-60 minutes for each bout in the heat (mean WBGT = 26.64 ± 4.71°C). The first 2 testing days consisted of two 1-hour trials per day, and the last 2 days consisted of three 45-minute trials per day so that data collection could be accomplished in the same amount of time each day. Exercise bouts were conducted during the same time of the day for all the trials. The exercise protocol varied between alternating games of soccer, ultimate frisbee, and bree-ball (a combination of ultimate frisbee and noncontact rugby). The subjects were permitted to drink water ad libitum from individualized water bottles throughout the exercise, choosing when to stop the activity to retrieve their water bottle from the sideline. The subjects were asked to put forth a maximum effort for the duration of each exercise bout.

The subjects were divided into 3 groups with their starting times beginning in 15-minute increments. Therefore, 6 subjects (group 1) entered the exercise bout initially (game of 3 vs. 3), 4 more subjects (group 2) entered the game 15 minutes later making a game of 5 vs. 5, and the final 6 subjects (group 3) entered the game 15 minutes after the second group did, making the game 8 vs. 8. Immediately after each exercise bout, the subjects jogged to a nearby restroom and inserted a rectal thermistor (10 cm past the anal sphincter) for the assessment of T re (Model 4600 YSI Inc., Yellow Springs, OH, USA).

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After insertion of the rectal probe, the subjects were randomly assigned to one of the cooling modalities (randomized crossover design). The cooling trials took place at 1 of the 3 locations at the testing site: under a covered pavilion (22.23 ±4.87°C [72.01 ± 2.90°F]): CWI, Shade, Emergency Cold Containment System® (ECCS), Rehab. Hood® (HOOD), Nike Ice Vest™ (NIV), ice towels (IT), ice buckets (IB); under a tent (22.51 ± 4.96°C [72.52 ± 2.22°F]): Port-a-Cool® (FAN) and Game Ready Active Cooling Vest™ (GRV); or next to the playing field with no shade (26.64 ± 4.71°C [79.95 ± 3.20°F]): Control (SUN). These sites were chosen because of convenience, as the FAN and GRV required an electrical outlet for use and therefore were placed under a tent in close proximity to an electrical outlet. No significant differences in WBGT readings were present upon the initiation of cooling between modalities (CWI: 26.71 ± 4.16°C; SUN: 26.30 ± 4.13°C; SHADE: 26.16 ± 3.97°C; FAN: 23.51 ± 2.14°C; ECCS: 26.86 ± 3.93°C; HOOD: 25.46 ± 3.89°C; GRV: 25.57 ± 4.04°C; NIV: 26.35 ± 4.41°C; IB: 27.44 ± 4.15°C; IT: 25.79 ± 3.50°C). Immediately upon arrival to the modality T re, HR, thermal sensation, and thirst sensation were recorded. After the initial set of measurements, the subjects were cooled by 1 of the 9 cooling methods (or control trial) for 10 minutes. During the 10-minute cooling phase, T re and HR were recorded every 2 minutes, whereas thermal and thirst sensations were recorded every 5 minutes. Hydration was not permitted during the cooling period.

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Cooling Modalities

Cold Water Immersion

The subjects were submerged, with only their head remaining out of the water, in a Rubbermaid® tub (150 gallons) with ice and water maintained at 14°C (58°F). A water temperature of 14°C was chosen because currently the literature exhibits no significant difference in cooling rates in varying water temperatures between 5 and 14°C (13,29,43). The tub was placed under the covered pavilion. The water was circulated every 2 minutes throughout the cooling process. The water temperature was monitored throughout the day, and adjustments were made as necessary to keep the water at 14°C (58°F).

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The subjects sat at a picnic table under the covered pavilion.

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The Port-a-Cool (Port-a-Cool® LLC, Center, TX, USA) is a large fan (dimensions: 67 in. height × 62 in. width ×32 in. depth; 170.2 cm × 157.5 cm × 81.3 cm) that provides cooling. The subjects were seated in chairs (8 ft.; 243.8 cm away from the device) under a tent in front of the Port-a-Cool for the 10-minute cooling period.

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Emergency Cold Containment System®

The ECCS (Chill Factor Performance Inc., Fort Myers, FL, USA) is a device that is doused with water to activate microbeads that are scattered throughout the lining of the unit and kept in a refrigerator or ice cooler before use. The ECCS is kept cool to 7-16°C (45-60°F) and provides arm portals for the easy monitoring of vital signs. The ECCS is approximately 5 ft. (152.4 cm) in length and encloses the head, arms, torso, and legs (amount of lower extremity enclosed varies depending on height of individual). The subjects were placed supine in the ECCS on a picnic table under the covered pavilion for the 10-minute cooling period.

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Rehab Hood®

The Rehab Hood® (Chill Factor Performance Inc.) is doused with water to activate microbeads that are scattered throughout the lining of the unit and kept in a refrigerator or ice cooler before use. The rehab hood spans from the forehead to the base of the posterior neck and covers the lateral head and the ears. The Hood was placed on the subject's heads, and they were seated at a picnic table under the covered pavilion for the 10-minute cooling period.

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Game Ready Active Cooling Vest™

The subjects sat in a plastic chair under the tent with the GRV (Game Ready™, Alameda, CA, USA) placed around their shoulders and torso. The front of the vest was zipped and then connected to a Game Ready Control Unit, which fills the vest with circulating cool water. The directions for amount of ice vs. water to be placed in the unit were followed as per manufacturers instructions and adjusted throughout the day to keep the circulating water at approximately 14°C (58°F), and the compression level was set to “low.”

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Nike Ice Vest™

The NIV (Nike, Inc., Beaverton, OR, USA) has 22 pouches that hold individual ice packs. The inner layer of the vest is made of Nike Dri-Fit™ material, which provides a layer between the skin and the ice packs. Adjustable straps allow for a relatively tight fit for each subject. The subjects sat at a picnic table under the covered pavilion with an NIV around their shoulders and torso.

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Ice Bucket

The subjects sat under the covered pavilion with their hands (up to the midforearm) and feet (up to the midcalf) in a bucket filled with ice and water. The water temperature of the bucket was measured with a thermometer and held constant at 14°C (58°F).

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Ice Towel

The subjects were positioned supine on a picnic table under the covered pavilion and had 7 cold, wet towels rotated on their head, neck, torso, and extremities. The towels were kept in a cooler filled with water and ice, and they were rotated at the 5-minute mark of cooling. The water temperature was monitored throughout the day, and adjustments were made as necessary to keep the cooler water at 14°C (58°F).

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SUN (Control)

The subjects were seated on a bench next to the playing field with no shade.

Monitoring: After the 10 minutes of cooling, the subjects were removed from the cooling modality and seated at a picnic table under a covered pavilion (for the Control trial, they remained in the sun) to be monitored for an additional 20 minutes. Although no cooling modality was administered at this time, this was done to observe the lingering effects of each cooling modality after it was removed. T re, HR, thermal sensations, and thirst sensations were recorded every 5 minutes during this time. As with the cooling phase, hydration was not permitted during monitoring. In addition, the ESQ was given at the 10-minute mark of the monitoring phase.

Recovery: After the 20 minutes of monitoring, the subjects were given a 1-hour recovery period in which they were permitted to eat and drink ad libitum before the next exercise bout. The same snacks and rehydration beverages were provided for the subjects on all the days. In addition, the same dinner was provided for all the subjects at the conclusion of each testing day. At the end of each recovery period, the subjects filled out the ESQ before beginning the next bout of exercise.

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Statistical Analyses

Statistical analyses were performed using paired sample t-tests (SPSS, Version 10.0, Chicago, IL, USA) to detect differences in T re, HR, and perceptual measurements after the 10-minute cooling phase. All 9 modalities (CWI, Shade, FAN, ECCS, HOOD, GRV, NIV, IB, and IT) were compared with the control trial (SUN). After Bonferroni corrections were implemented, the level of significance was set at 0.006. All data are presented as mean ± SD.

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The average T re after exercise across all trials was 38.73 ± 0.12°C (102 ± 0.21°F) and was not significantly different (p > 0.006) between subjects before the start of each cooling modality. After 10 minutes of cooling, the differences in T re from baseline (0 minutes of cooling) to 10 minutes of cooling for CWI (−0.65 ± 0.29°C [−1.17°F]; p = 0.005), ECCS (−0.68 ± 0.24°C [−1.22°F]; p = 0.002), and IB (−0.74 ± 0.34°C [−1.33°F]; p = 0.005) were significantly greater compared with SUN (−0.42 ± 0.15°C [−0.75°F]). Although the Shade (p = 0.475), FAN (p = 0.767), HOOD (p = 0.616), GRV (p = 0.893), NIV (p = 0.020), and IT (p = 0.042) were not significantly different (p > 0.006), they all provided greater decreases in T re compared with that in SUN (Figure 1).

Figure 1

Figure 1

In addition, we expanded the results to show a relationship of the amount of time it took each modality to reduce the body temperature 1°F (Figure 2). For example, although it took CWI and IB approximately 8 minutes to decrease the core body temperature 1°F, it took 13 minutes for the SUN to accomplish the same reduction.

Figure 2

Figure 2

The average HR before cooling was 147 ± 9 b·min−1. The average HR after exercise across all the trials was HR at 10 minutes of cooling was significantly lower (p < 0.006) for CWI (82 ± 15 b·min−1; p = 0.001), ECCS (87 ± 14 b·min−1; p = 0.001), and IT (84 ± 15 b·min−1; p = 0.001) compared with that for SUN (101 ± 15 b·min−1) (Figure 3).

Figure 3

Figure 3

After 10 minutes of cooling, thermal sensation scores between modalities were all significantly lower (p < 0.006): CWI (p = 0.001), FAN (p = 0.001), ECCS (p = 0.001), HOOD (p = 0.001), GRV (p = 0.001), NIV (p = 0.001), IB (p = 0.001), IT (p = 0.001) compared with that for SUN, except for Shade (p = 0.010) (Table 1).

Table 1

Table 1

There were no significant differences (p > 0.006) in prethirst and postthirst sensations between modalities compared with that for SUN (Table 1).

The ESQ scores were significantly lower (p < 0.006) for CWI (p = 0.003), FAN (p = 0.003), and IT (p = 0.001) compared with that for SUN. A summary of perceptual data can be seen in (Table 1).

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The purpose of this study was to evaluate the effectiveness of various cooling methods, compared with that of a control, in their ability to lower the T re of individuals after exercising in the heat. The design of this study focused on a brief body cooling phase (10 minutes) to mimic the length of a halftime period found in many sporting events. Our results successfully identified efficient and practical methods of reducing T re during this time, which limited the amount of time the body was subjected to physiological stressors associated with hyperthermia, primarily high core body temperature and elevated HR.

At present, it is well documented and well accepted that CWI provides faster cooling rates for treating hyperthermic athletes when compared with other modalities (3,6,9,10). However, although these studies have validated CWI as the most effective treatment modality when treating EHS, evidence is not as clear when examining cooling modalities for their effectiveness and practicality of cooling mildly hyperthermic individuals. For example, CWI may not be a practical option for cooling athletes during a short halftime period because of uniform restrictions, quantity of immersion tubs needed, etc. In addition, using CWI to cool mildly hyperthermic athletics may result in an initial decrease in performance because of a decrease in muscle temperature and an uncomfortable perception of cold (43). Therefore, it is imperative to determine which cooling modalities are most practical in effectively lowering the core body temperature of a hyperthermic athlete while aiding in recovery after exercise in the heat.

In this study, the average postexercise temperatures of subjects entering the cooling phase were similar for each modality (38.73 ± 0.12°C [102 ± 0.21°F]). After the 10-minute cooling phase, T re after CWI was significantly lower when compared with that of SUN. This decrease in T re from CWI supports the findings of the existing literature showing the success of rapidly decreasing body temperature in hyperthermic athletes using this method (10,29,43).

It has been well documented that CWI has not only contributed to a rapid decrease in core body temperature after exercise but also to improved cardiovascular capabilities (10,42). This is evident because the hydrostatic pressure and vasoconstriction of the capillary beds from CWI causes the displacement of fluids from the extremities toward the central cavity. This fluid shift results in an increased cardiac output and a reduction in peripheral resistance, leading to more rapid cardiovascular recovery and decreased cardiovascular strain (42). This response will likely be heightened when an individual is placed in thermoneutral water.

The temperature gradient between the CWI and the warm temperature of the skin also greatly contributes to the effectiveness of this modality (10,42). Although the cooling results of CWI in our study were comparable with those of previous research in its effectiveness to adequately lower T re, our results showed lower cooling rates (0.06 ± 0.04°C/min) compared with those of previous studies (10,13,20,29,30,43). This difference likely occurred because our subjects only reached a level of mild hyperthermia (mean 38.73 ± 0.12°C [102°F]), keeping the temperature gradient between water and the subject low. In addition, this response may also have been present if initial skin temperatures were low. Therefore, the body likely defended itself from a drastic decrease in T re more than it normally would if suffering from severe hyperthermia (>40°C [104°F]).

In the shade trial, the decrease in T re was not significantly different compared with that of SUN. Bringing an athlete or team to a shaded area is common during a halftime or between games or events. To our knowledge, few athletes use other cooling methods either during or in between athletic events. For example, during most halftimes or in between games, many athletes will seek shade by means of sitting under a tree or going inside a locker room.

Our findings demonstrated that in the shade, T re decreased from the start to the finish of the cooling phase; however, the cooling provided by other modalities provided a faster decrease in T re (Figure 2). This information should be provided to athletes who exercise or compete in the heat to encourage them to consider other cooling options during a halftime or a break in games.

Although the FAN lowered T re after 10 minutes of cooling (−0.04 ± 0.02°C), these values were not significant (p = 0.077) compared with those of SUN. Although many variations have been attempted for this method (i.e., fan with water spray, fan with ice packs, fan with wet towels, etc.), cooling rates (0.03-0.11°C/min) have been fairly consistent with a similar methodology (12,23,27,34,35). In this study, an average of 15 minutes was required for the FAN to lower the subject's T re 1°F.

After the 10-minute cooling phase, T re for the ECCS was significantly lower (−0.68 ± 0.44°C [1.22° F]; p = 0.002) when compared with that of SUN. To our knowledge, this is the first study to evaluate the cooling rate of the ECCS. Although further research must be done on this product, our results indicate that the ECCS is an acceptable means to reduce the core body temperature of a mildly hyperthermic individual.

To our knowledge, this study was the first in which the Rehab. Hood® has been examined as a means to cool a hyperthermic athlete. At the end of the cooling phase, the HOOD was the only device that had a slower cooling rate than SUN did. It can be hypothesized that the unfavorable results were because of the inability of the body to dissipate heat through the head.

Cooling vests are common in the use of precooling core body and skin temperature before exercise events. Although many studies have evaluated the effects of cooling vests for precooling purposes (5,11,16,20,22,24,28,40,41) there is little known research on the effect of cooling vests on postexercise body cooling. The GRV and NIV that we evaluated did not show significant differences compared with that of SUN. Lopez et al. (24) found the cooling rate of the vest to be 0.03°C/min, and this contributed to no significant difference compared with a control group (no vest). Our study involving the GRV and NIV showed similar cooling rates (0.04 and 0.05°C/min, respectively) with similar testing conditions. For example, rectal temperature was used in both studies, immediate transition from exercise to the initiation of cooling was implemented, and the subjects exercised to a similar core temperature before the initiation of cooling (38.8 vs. 38.73°C). Furthermore, both studies resulted in nonsignificant effects in lowering the T re after exercise in the heat.

In comparison with CWI and ECCS, IB also showed a significant decrease in T re after the 10-minute cooling period (−0.74 ± 0.62°C [1.33°F]; p = 0.005) compared with SUN. In a similar study, cooling rates were examined in firefighters who exercised in the heat and cooled using hand and hand with forearm immersion. The authors concluded that cooling the hands and forearms had greater reductions in T re compared with that of the hand-only immersion group (36). In addition, other studies examined partial immersion by means of lower extremity immersion (1,7,14,21,23,36) Separate studies using this method report decreases in T re; after exercising subjects were either precooled or cooled postexercise (14,21,26,31). With these separate studies all finding positive results by cooling either hands and forearms, or legs, we cooled both arms and legs simultaneously in this study to maximize the benefits resulting from this cooling method. In addition to their efficiency, IBs also provide a practical means to body cooling. For example, they are quick and easy to use, and athletes would not have to change uniforms because only the forearms and lower legs are immersed.

This modality has also been used in previous studies, but it has been examined more often as a means to treat EHS than to cool a mildly hyperthermic athlete after exercise in the heat. The IT did decrease the subject's T re after cooling (−0.58 ± 0.57°C [1.04°F]); however, the decrease was not significant (p = 0.042) compared with that of SUN. One possible reason for this could be that, although the towels were rotated in ice water, it was often difficult to keep the temperature of the ice water constant. This method may also be challenging to administer between exercise bouts or during a halftime because the athlete would again have to remove equipment or uniforms.

The combination of exercise and high environmental temperatures creates stress on the body. As an individual exercises, the body produces more heat than it dissipates resulting in an increase of core body temperature. To effectively dissipate heat during exercise, sweat must be produced to wet the skin and blood must be shunted from the core to the periphery (2). The redistribution of blood to the periphery lowers central blood volume (32). To maintain an adequate cardiac output during exercise, HR subsequently increases to offset the decreased stroke volume (2,42). This interaction causes cardiovascular strain and decreased performance.

Because this is a normal response to intense exercise, our subjects were likely in a state of cardiovascular strain at the end of the exercise bout, as exhibited by their elevated HRs. Therefore, along with rapidly reducing T re, we were also focused on quickly returning their HR to baseline measures. When the cooling phase began, all the subjects entered with an elevated HR compared with their baseline (precooling) measures. In addition, the average starting HR of subjects was similar (no significant differences) for each modality. After 10 minutes of cooling, HRs after CWI (−80 ± 16 b·min−1; p = 0.001), ECCS (−64 ± 17 b·min−1; p = 0.001), and IT (−67 ± 15 b·min−1; p = 0.001) were significantly lower when each respective modality was compared with SUN. Because these modalities provided significant decreases in HR compared with that for SUN, it can be hypothesized that athletes would be at a physiological benefit when entering a subsequent bout of exercise, potentially resulting in increased performance.

The significant decreases in HR resulting from CWI, ECCS, and IT (compared with SUN) may have allowed the shift in blood volume to return centrally, reducing cardiac strain. This is an important component in the efficacy of cooling modalities (42), especially if used during a short break or halftime situation. These cardiovascular responses allow the individual to return to exercise in a normal (or near normal) state, whereas if their HR remained elevated, cardiovascular capabilities would be diminished which would likely lead to a decrease in exercise performance or potential heat illness (i.e., heat exhaustion).

Although significant decreases in HR were shown with CWI, ECCS, and IT, the effects could have been influenced by the postural position of the subjects. It is well documented that the position of the body can influence HR, and more specifically plasma volume (2). In the case of our subjects, central blood volume may have been lower due to exercise (blood volume shifts to the muscles and periphery). If this were the case, venous return would have been lower resulting in a greater HR to offset this deficit. As with differences in postural positioning, central blood volume may return more quickly resulting in a more rapid return to the baseline HR. For example, the subjects being cooled via Shade, FAN, HOOD, GRV, NIV, IB, and SUN were all in a seated position (∼90°), whereas the subjects being cooled via CWI were in more of an inclined position (∼45°), and the subjects being cooled via the ECCS and IT were in a supine position. Therefore, it can be hypothesized that the supine position of the ECCS and IT may have contributed to a faster decrease in HR, whereas those methods involving subjects to be seated upright may have taken more time to return to baseline levels.

The reduction in cardiac strain that was evident through the significant decrease in HR may further be supported by our observed change in ESQ scores (preexercise to postcooling). As CWI, FAN, and IT showed these decreases in HR, they also resulted in significant decreases of ESQ scores compared with SUN. These results may further contribute to the potential for increased performance during a second bout of exercise. With lower ESQ scores signifying less physiological strain, perceived fatigue may also be less evident. The psychological benefits of less perceived fatigue may further enhance the physical capabilities of a second bout of exercise.

In addition to decreased ESQ scores with the CWI, FAN, and IT treatments, lower thermal sensation scores were present. Thermal sensation naturally increased during exercise because of both the high ambient temperatures and the increase in metabolic heat production from exercise. When compared with the control trial, CWI, FAN, ECCS, HOOD, GRV, NIV, IB, and IT resulted in significant decreases in thermal sensation.

The results of our study may provide an insight into instruction for effective methods of cooling athletes during a brief rest period or halftime scenario. The combination of decreased T re, decreased HR, and decreased thermal sensation that was obtained after only 10 minutes of cooling can greatly contribute to better physiological capabilities, which may result in an enhanced performance in many athletic events.

Given that this study was a field study, certain limitations were inherent. For instance, the starting temperatures of our subjects before cooling were slightly lower (38.73 ± 0.12°C [102 ± 0.21°F]) than those of previous studies (13,15,29,32,33,39,43). Furthermore, overall environmental temperatures were somewhat low (26.64 ± 4.71°C). During the trials wherein ambient temperatures were lower, body temperatures were also lower at the end of exercise. Moreover, intensity was not controlled during the exercise bouts. Therefore, some subjects may not have been exercising at a high-enough intensity to sufficiently increase their core body temperature. In addition, the 9 cooling modalities that were examined were all administered either under a tent or under a covered pavilion. Therefore, the cooling rate may have been partially influenced by this environment. Finally, the temperature of the CWI bath may have prohibited maximal cooling. Although some studies (13) have shown that water temperature is not significant in the rate of body cooling, other studies (15,29,32,33,39,43) contradict this theory. Future research studies should investigate the effects of these cooling modalities in a more controlled setting.

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Practical Applications

Although CWI has supported the findings of previous literature in its effectiveness to quickly lower core body temperature of hyperthermic athletes, we also found alternate methods that provided similar results and may be used in cases of nonemergency, mild hyperthermia (<40°C [104°F]) if CWI is unavailable or is not applicable. For example, CWI may be difficult to administer in between 2 exercise bouts (i.e., halftime) because of equipment or uniforms that would have to get wet or be removed such as in football or hockey. In the context of these cases, other cooling modalities that are less troublesome but equally efficient may be considered. Coaches, athletic trainers, and other team personnel can use this information as a way of potentially improving performance of their athletes during subsequent bouts of exercise. Our results suggest that CWI, ECCS, and IB provides adequate cooling for a mildly hyperthermic athlete during a brief cooling period.

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heat stress; cooling rates; thermoregulation

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