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.
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:© 2010 National Strength and Conditioning Association
hyperthermia; athletic performance; precooling