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Effect of Body Cooling on Subsequent Aerobic and Anaerobic Exercise Performance: A Systematic Review

Ranalli, Gregory F1; DeMartini, Julianne K1; Casa, Douglas J1; McDermott, Brendon P2; Armstrong, Lawrence E1; Maresh, Carl M1

Journal of Strength and Conditioning Research: December 2010 - Volume 24 - Issue 12 - p 3488-3496
doi: 10.1519/JSC.0b013e3181fb3e15
Brief Review

Ranalli, GF, DeMartini, JK, Casa, DJ, McDermott, BP, Armstrong, LE, and Maresh, CM. Effect of body cooling on subsequent aerobic and anaerobic exercise performance: a systematic review. J Strength Cond Res 24(12): 3488-3496, 2010-Body cooling has become common in athletics, with numerous studies looking at different cooling modalities and different types of exercise. A search of the literature revealed 14 studies that measured performance following cooling intervention and had acceptable protocols for exercise and performance measures. These studies were objectively analyzed with the Physiotherapy Evidence Database (PEDro) scale, and 13 of the studies were included in this review. These studies revealed that body cooling by various modalities had consistent and greater impact on aerobic exercise performance (mean increase in performance = 4.25%) compared to anaerobic (mean increase in performance = 0.66%). Different cooling modalities, and cooling during different points during an exercise protocol, had extremely varied results. In conclusion, body cooling seems to have a positive effect on aerobic performance, although the impact on anaerobic performance may vary and often does not provide the same positive effect.

1Korey Stringer Institute, Department of Kinesiology, University of Connecticut, Storrs, Connecticut; and 2Department of Health and Human Performance, University of Tennessee at Chattanooga, Chattanooga, Tennessee

Address correspondence to Gregory Ranalli, gregory.ranalli@gmail.com.

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Introduction

Recent research studies have explored different ways to cool a hyperthermic athlete to enhance performance. The combination of exercise and high environmental temperatures creates stress on the human body, and this stress is countered by physiological responses from the body (3). It is thought that precooling an athlete, or cooling an athlete during rest periods, can improve subsequent performance during an athletic game or competition.

To show 1 example of how cooling may impact an athlete, imagine the halftime of a soccer match (ca. 10-minute duration). It is not unlikely for athletes to experience a body temperature of 103°F (39.4°C) after one-half of soccer in a hot environment. If 1 team uses a cooling modality that provides an adequate cooling rate (i.e., 0.10°C·min−1) (2), but a second team uses a substandard cooling modality that only provides a cooling rate of 0.03°C·min−1 (6), players on the first team will have a physiological advantage at the beginning of the second half of play because they were better cooled during the rest period.

To take a more in-depth look at how this soccer athlete could gain a physiological advantage, consider the above scenario. An athlete comes off the soccer field for halftime with a body temperature of 103°F (39.4°C). Using the aforementioned information on a cooling modality that provides an adequate cooling rate and drop in heart rate, the athlete would return to the field with an internal temperature of 101.1°F (38.4°C) at the end of the 10-minute halftime. However, if he were cooled using a substandard cooling modality, he would return to the field with a body temperature of 102.4°F (39.1°C) (2,6).

With these facts in mind, it is important to determine how body cooling could physiologically benefit a hyperthermic athlete. Currently, 2 theories prevail. The first theory states that the athlete reaches a critical limiting temperature during exercise and becomes fatigued (10,11). The research behind this theory shows that even when athletes begin an exercise bout at varying core body temperatures, they ultimately fatigue and cease exercise upon reaching a similar internal temperature of approximately 40°C (11). In a study examining this theory, test subjects were men of average size (77.9 ± 6.4 kg, 187 ± 6 cm) who were exercising in a controlled environmental chamber without any uniforms or equipment of any kind (11). It is possible that a larger individual, such as a football player practicing in full pads outdoors in the heat of the summer, may reach a lower critical limit and fatigue, being forced to terminate exercise even before hitting the 40°C point. An athlete such as the football player described here may be an example of the kind of athlete that could benefit the most from body cooling during exercise.

The critical limiting temperature has been refuted recently by a study examining a group of runners and their performance in varying temperatures. This research found no differences in the final 600 m of a run regardless of the subjects' temperature being ≥40°C (9). The results of the study concluded that runners were able to maintain their running velocity throughout the trials despite a rectal temperature (T RE) that was greater than the proposed threshold of 40°C. The authors of this study went on to state that the results of studies supporting the 40°C threshold were not only based on core temperature alone but they also included an elevated skin temperature (TSK) and substantial cardiovascular strain (9).

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 (16,24,25). Often, this theory is thought to involve longer, endurance type exercise where the athlete adjusts pacing strategies to complete the exercise and avoid reaching a critically high body temperature (23-25).

The ability of runners to pace themselves during a race such as a marathon is one of the key points made by research arguing for central anticipatory control (17). It is argued that if a runner was limited by chemical factors from exercising muscles or the brain, which produces the fatigue and termination of exercise, marathon runners would begin at a fast pace and run as long as the body could handle it. This is not true however, as marathon runners pace themselves and are even able to speed up and accelerate toward the end of the race, which shows the body's ability to anticipate and react accordingly (17). This ability of runners to pace themselves to be able to finish a marathon, and even accelerate toward the finish line supports the central anticipatory theory (17,23-25).

There has also been recent evidence shown that does not support this anticipatory theory, arguing the “feedforward” mechanism that is said to exist during exercise in the heat. This evidence has been reviewed and summarized in detail stating that the only evidence of an anticipatory control of exercise is resulted from an early elevation of T SK (15). It is acknowledged, however, that an anticipatory reduction in the intensity of exercise may exist because of the early changes in brain or muscle temperature, with the authors simply stating that there is just no evidence to support this theory (15).

The idea of initiating body cooling with an athlete who has been or who will be exercising in the heat would have an effect on both theories. It is thought that precooling an athlete before exercising in the heat will allow that athlete to begin at a lower core body temperature, which would allow a longer duration of exercise because reaching a limiting temperature would be delayed by beginning exercise at a lower temperature. Obviously, body cooling between exercise bouts (such as a half time) would have the same effect, ideally lowering an athlete's core body temperature to allow him or her to return to their athletic environment at a lower core body temperature and thus giving them the ability to exercise in the heat for a longer duration.

The practice of body cooling for performance benefits is relatively new to athletics. Although data are available on this topic, varying results have been reported, and the most effective methods are yet to be determined. Valid recommendations for athletes cannot yet be made. Therefore, the purpose of this systematic review is to analyze the effect of various body cooling modalities on athletic performance and provide insights regarding which methods effectively enhance performance. This review will serve as a summary of the available literature and provide the reader with a clear guide to the possible impacts on athletic performance as shown in the available literature.

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Methods

We searched the following databases in February of 2010: MEDLINE, SportDiscus, CINAHL, Scopus, and Web of Science. For the search we used the following search terms in varying combinations: exercise, athletics, athletes, sports, running, cycling, football, weight lifting, sprinting, tennis, soccer, aerobic, anaerobic, swimming, race, track and field, athletic performance, speed, endurance, time-trial, distance, precooling, body cooling, ice vest, water immersion, ice packs, cooling, ice water, and cold water immersion (CWI). The search results were combined with other articles obtained through an examination of various reference lists. We then prescreened abstracts from articles obtained through our searches to eliminate studies that did not meet our inclusionary and exclusionary criteria.

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Inclusionary Criteria

Specific inclusion criteria identified before data analysis included (a) original research, (b) human subjects, (c) randomized control design, (d) aerobic or anaerobic exercise, (e) performance was measured, (f) controlled hydration (g) cooling was administered before, during, or between exercise bouts.

We did not include review articles, textbooks, or case studies in the overall data analysis. Studies that used cooling for treatment of heatstroke or as a means to induce hypothermia were also excluded. Studies involving passive hyperthermia were excluded so that results from exercising conditions would reflect traditional athletic competition settings. In addition, those individuals who were passively heated may respond differently to body cooling than those who had exercised induced hyperthermia. Studies were also excluded if hydration was not controlled, as previous studies have shown that hydration may impact cooling and thermoregulation for individuals exercising in the heat (21). Animal studies were not included and studies involving wheelchair subjects or subjects suffering from multiple sclerosis were also excluded due to the fact that spinal cord-injured athletes are different thermoregulators than able-bodied athletes in hot environments (19).

Abstracts of the 228 identified papers were included in this review only if they met all inclusion criteria previously identified. A total of 59 abstracts met these criteria (Figure 1). Upon full text review of these articles, it was determined that only 14 studies met all criteria. A quality assessment review of these 14 studies followed.

Figure 1

Figure 1

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Quality Assessment

Two reviewers independently analyzed and scored the methodological quality of the 14 remaining studies that did not meet our inclusionary and exclusionary criteria. Quality was based on the Physiotherapy Evidence Database (PEDro) Scale (Table 1) (18). This scale consists of a checklist to determine 2 aspects of a study's quality: (a) the internal validity of the trial and (b) whether information is sufficient to interpret the results. Articles were not included if they scored lower than 6 of possible 10 on the scale. A score of 6/10 was chosen because complete blinding of participants and therapists is impossible when assessing body-cooling modalities. For example, subjects cannot be blinded as to whether or not they are or are not wearing a cooling vest, or whether they are or are not immersed in a water bath. Likewise, assessors also cannot be blinded as to whether or not the subjects are or are not subjected to a cooling modality. Therefore, the maximum score attainable was 7/10.

Table 1

Table 1

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Results

One study was eliminated because of a PEDro score of 5 (12). As a result, 13 original studies were included for this review, as shown in Tables 2 and 3. Nine of the 13 studies used cycling in a warm environment (4,5,7,13,14,20,22,27,28), 2 involved outdoor distance runs (1,29), 1 used treadmill running indoors (26), and 1 used outdoor intermittent sprints (8).

Table 2

Table 2

Table 3

Table 3

Exercise performance was measured differently throughout the studies included in this review. Nine of the included studies looked at aerobic performance (Table 2) and the effect of cooling on total exercise time, time to exhaustion, power output, or total work (1,8,13,14,20,26-29), whereas 6 involved anaerobic exercise (Table 3), which evaluated the effects of cooling on total work, power output, distance covered, or sprint time (4,5,7,8,22,26). Two of the studies used both aerobic and anaerobic exercise protocols (8,26).

Although this review involves 13 studies, some of the studies used multiple cooling modalities. Throughout the varying methods, cooling resulted in an increase in exercise performance in 16 of the 27 different cooling sessions (1,4,8,14,20,26-29). Ten sessions resulted in no significant differences in exercise performance (4,5,7,8,13,20,22,26,29), and 1 session reported that cooling significantly decreased exercise performance (22). These results can be seen in Tables 2 and 3 and in Figures 2 and 3.

Figure 2

Figure 2

Figure 3

Figure 3

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Discussion

Six of the 13 studies in this review used CWI (or ice water immersion [IWI]) as a cooling method (4,8,20,27-29). Two of the studies compared water of varying temperatures (27,29), whereas most of the studies compared CWI to another cooling modality, or used CWI in combination with another modality (4,8,20). In one study, Vaile et al. (27) compared different temperatures of water across 4 trials (10°C intermittent, 15°C intermittent, 20°C intermittent, 20°C continuous), and comparing intermittent immersion (1 minute in bath, 2 minutes out; cycle repeated 5 times for a total of 15 minutes) to continuous immersion (immersed in bath for 15 minutes). These modalities were compared to an active recovery period, both of which were conducted between 2 bouts of exercise. The results showed that active recovery resulted in a 4.1% decrease in total work performed from exercise task 1 to task 2, whereas the CWI allowed for maintenance of work performed. Although the study showed a significantly greater amount of work done in the second exercise task for CWI compared to active recovery, no differences were found between different temperatures or intermittent vs. continuous exercise (27).

Another study conducted by Vaile et al (28) compared CWI with an active recovery period between bouts of cycling in the heat. Although this study also examined rectal temperature, heart rate, blood lactate, and limb blood flow, this review focused on the performance results, which included the difference in total work performed over 2 sessions separated by the cooling or active recovery period (28). Vaile et al. found that active recovery caused a significant decrease in the performance element of their study from the first exercise bout to the second, whereas CWI had a slightly positive increase, although it was not a statistically significant increase (28).

Ice water immersion was compared with CWI in a study conducted by Yeargin et al (29). In this protocol, the subjects ran for 90 minutes in the heat before they were cooled for 12 minutes in either CWI (13.98°C) or IWI (5.23°C). After cooling the subjects ran again, this time in a set distance performance trial. The CWI resulted in significantly faster performance times compared to control; however, IWI provided no benefit. This could have been because the IWI subjects stated that they felt “stiff and cold” after the cooling; it was estimated by the authors that this lead to slower performance times (29).

Two studies examined CWI and an ice vest or cooling jacket, and also included trials consisting of a combination of the 2 (8,20). Quod et al. (20) used 2 trials, where subjects were precooled using a cooling jacket for 40 minutes, and another which used CWI for 30 minutes followed by a cooling jacket for another 40 minutes. No significant differences were found with the cooling jacket; however, the combination trial resulted in significantly faster time trial performances while cycling in the heat (20). A similar protocol was used by Duffield and Marino (8). Subjects in this protocol were precooled with an ice vest for 15 minutes, which included a warm-up and stretching period, and they also wore the ice vest during a 10-minute “halftime” between exercise sessions. In the second trial, subjects were precooled using CWI for 15 minutes, followed by an ice vest during the warm-up and stretching period, and they also wore the ice vest during the halftime break. Unlike the previously mentioned study, this study found no significant differences between trials (8).

Castle et al. (4) found no significant benefits using CWI compared to an ice vest and to ice packs covering the lower legs. In this study, subjects were precooled for 20 minutes before cycling in the heat for 20, 2-minute sprint protocols. Cold water immersion did not provide a significant difference in exercise performance, whereas the other modalities provided significant benefits (4).

An ice vest, a cooling vest, and a cooling garment have also been evaluated for their impact on exercise performance (1,4,5,7,8,13,20,22). Four studies involved trials with cooling vests only (1,5,7,13), whereas 4 other studies included vests with a combination of cooling methods in different trials (4,8,20,22). In those that studied the effects of only a cooling vest or jacket, 2 involved aerobic exercise protocols, whereas the other 2 involved anaerobic exercise protocols. Interestingly, it was found that both aerobic protocols provided significant performance benefits (1,13), whereas both anaerobic protocols did not find significant results (5,7). Arngrimsson et al. showed that precooling before a 5-km race provided significant decreases of gastrointestinal temperature (T GI) before the race, and lower T GI at the end of the race and faster race times (1). Likewise, Hornery et al. found increases in performance measurements; however, physiological measurements were not different between groups (13).

Two studies, which compared the effects of a cooling vest or jacket vs. a control group, showed no significant results in exercise performance (5,7). One study examined the effects of an ice jacket on intermittent cycling sprints and found that while thermal and thirst sensation were lower in the cooling group, no significant differences were found in rectal temperature (T RE), skin temperature (T SK), rate of perceived exertion (RPE), or performance measurements (7). Likewise, Cheung and Robinson also found no significant differences in performance measurements or physiological marks after cooling prior to a repeated sprint performance protocol. However, significant differences in T RE and T SK were noted immediately after precooling, with these differences no longer apparent once exercise began (5).

As previously mentioned, four studies included in this review compared a cooling jacket or vest to other cooling methods (4,8,20,22). Of these 4 studies, 1 of the protocols involved aerobic performance (20), whereas the other 3 involved anaerobic performance (4,8,22). In the study using an aerobic protocol, Quod et al. (20) compared the effects of a cooling jacket, CWI, and a combination of the 2. No significant effects on performance occurred because of wearing the cooling vest, but the study did show a significant increase when combined with the second method (cooling jacket + water immersion) (20). Conversely, in the 3 studies that looked at the effects of a cooling jacket on anaerobic performance (4,8,22), only 1 reported that cooling provided significant increases of exercise performance (4).

Alternate methods, such as the rapid thermal exchange (RTX), ice packs, and a neck-cooling device have been studied. The RTX is a hand-cooling device, which uses the combined application of negative pressure and a heat sink to increase heat exchange between the circulating blood and the external environment (14). As a result, the cooled blood is delivered directly to the body core via venous return. Because this principle applied to the involved study, it was found that the use of the hand cooling unit lowered tympanic temperature (T TYM), lactate concentration, and oxygen uptake during a submaximal steady rate test (1-hour cycling at 60% O2max), and also reduced the time it took to complete a 30-km cycling time-trial test.

In addition to the RTX, ice packs, ice cuffs and a neck-cooling device also have been used to determine the effects of precooling on exercise performance. Castle et al. (4) found that precooling leg muscles before intermittent cycling sprint protocols improved sprint exercise performance. As previously mentioned, these effects were compared to 2 other methods of precooling (ice vest and CWI) and a control (i.e., no cooling). Moreover, results showed that the rate of heat strain increase was slower in those who were precooled via the ice packs and CWI: A blunted rise of muscle temperature also was observed. These results led to the conclusion that leg precooling offered the greatest ergogenic effect on peak power output, when compared to the other methods (4).

Conversely, Sleivert et al. (22) reported impaired exercise performance when precooling the leg muscles. In this protocol, water-perfused cuffs were used, as opposed to ice bags in the Castle et al. study (4). The impairment of anaerobic exercise performance in this study was attributed to the decrease in muscle temperature in the leg-cooling group, when compared to a control group and also to groups in which alternated cooling methods.

Lastly, one study evaluated the effects of a neck-cooling device on total distance run on a treadmill (26). This neck-cooling device significantly increased the total distance covered during the run. Conversely, when the neck device was worn but not cooled, no change in performance occurred.

The majority of current literature evaluating the effects of body cooling on exercise performance involves aerobic exercise (1,8,13,14,20,26-29). As seen throughout this review, the studies that used aerobic exercise generally showed improvements in exercise performance, with 7 of 9 having significant results (1,14,20,26-29). The percentage difference between body cooling and control in aerobic exercise performance studies is depicted in Figure 2.

The effect of body cooling on aerobic performance also has been evaluated during rest periods. The reader should note that cooling both before and during exercise leads to a longer amount of time that subjects were cooled, vs. the methods that were most frequently used during anaerobic studies, which are outlined below.

Most of the studies involving anaerobic exercise have focused on cooling before exercise bouts (4,5,7,8,22), as shown in Table 3. Although these results are not similar to aerobic studies (i.e., with 5 of the 6 studies exhibiting no significant increase in anaerobic performance because of body cooling), more than half of the trials in Figure 3 show that body cooling had a small, nonsignificant impact. It should also be noted that 1 study (22) found a significant decrease in anaerobic performance. This involved cooling the subjects' thighs before exercise, with a decrease in the temperature of the active muscles.

As stated above, although some anaerobic studies show an increase in performance, only 1 of 6 studies included in this review reported a significant increase in performance (4). This study involved various modes of precooling before intermittent sprint exercises, and it was concluded that there was a decrease in the rate of heat strain experienced by the subjects, a decrease in muscle temperature, and an increase in peak power output. These results occurred only when an ice vest was worn and when ice packs covered the legs (4).

The varied findings of these anaerobic exercise studies may be attributed to several factors, such as the length of time that the cooling was performed, when cooling was initiated (precooling or between intermittent bouts), the mode of cooling (effectiveness based on cooling rate), and the means by which exercise performance was measured. For example, the mode of cooling and the length of cooling likely would have directly affected the decrease of internal temperature and skin temperature.

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Practical Applications

Based on the studies included in this review, no single cooling modality definitively offers superior improvements of performance. With that being said, it is necessary to keep in mind the fact that different exercise modes, intensities, and durations may benefit from different cooling modalities and different lengths of cooling.

This review shows that aerobic exercise can be enhanced with the use of cooling modalities (Figure 2). The CWI, cooling vests, cooling collars, and the RTX have all provided subjects with some exercise benefits. Combining multiple modalities may provide even more of a benefit to performance, when used before and in between exercise bouts. Many of these modalities (e.g., CWI, water immersion, cooling vests, cooling garments) could be used during breaks in events, such as track and field, or during a halftime of events such as soccer, which are contested outdoors in hot environments.

Cooling does not appear to provide the same degree of performance benefits when applied before or during anaerobic exercise (Figure 3). It is also possible that altering the cooling modalities or the length that the subject is cooled may provide some different, positive results in future research. Such methodical changes would allow a more accurate interpretation of the results from using different cooling modalities with different forms of exercise.

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Keywords:

hyperthermia; athletic performance; precooling

© 2010 National Strength and Conditioning Association