At present, views conflict as to the best mode of rapidly cooling hyperthermic athletes. Given that immersion is a widely accepted mode of body cooling, endorsed by organizations such as the American College of Sports Medicine, the International Amateur Athletic Federation, and the United States Military, we conducted this study to determine whether ice-water immersion or cold-water immersion is superior in cooling hyperthermic runners. The cooling rates found in this study are consistent with immersion cooling rates found by other investigators. In soldiers suffering from heat stroke with Tre
of 41°C or higher, ice-water immersion had a cooling rate of 0.15°C·min−1
with a mean time of 19.2 minutes of immersion.5
In an earlier study, male and female distance runners with a preimmersion Tre
of 41.7 ± 0.2°C were cooled at rates of 0.20 ± 0.02°C·min−1
in ice water (1 to 3°C) for 5.6 ± 0.6 minutes.15
We found that cooling rates with torso immersion in cold water were similar to those in a recent study.23
The cooling rates we found for ice-water immersion and cold-water immersion are greater than reported cooling rates for other modes of cooling: passive cooling (0.054°C·min−1
), 6 cold packs placed on large arteries of the neck, axillae, and groin (0.049°C·min−1
), body covered with 24 to 48 cold packs (0.074°C·min−1
), evaporative cooling in which water was splashed onto the body and evaporated by a compressed air spray (0.081°C·min−1
), evaporative cooling plus 6 cold packs (0.086°C·min−1
), and whole-body immersion at 25°C (0.075°C·min−1
Whole-body immersion at 12°C (between our 2 temperatures) had a significantly greater cooling rate (0.262°C·min−1
< .01) than the other modes of cooling.8
In the only previous study comparing ice-water immersion and cold-water immersion cooling rates, researchers found no difference between ice-water immersion (1 to 3°C) and cold-water immersion (15°C to 16°C) in dogs.17
With similar Tre at the start of all immersions, we found that ice-water immersion (0.16 ± 0.01°C·min−1) and cold-water immersion (0.16 ± 0.01°C·min−1) at 12 minutes induced cooling rates that were both significantly greater (P < .05) than mock immersion (0.10 ± 0.01°C·min−1), although ice-water immersion and cold-water immersion cooling rates were not significantly different from each other (P > .05) (see Table ). The significant difference between ice-water immersion and cold-water immersion cooling rates as compared with mock immersion was not observed until after 8 minutes of immersion. This implies that hyperthermic athletes being cooled by immersion in water at 5° or 14°C may need to be immersed for longer than 8 minutes. In addition, in the ice-water and cold-water immersion groups, rectal temperatures continued to decrease significantly faster postimmersion. Thus, water-immersion times similar to our protocol may provide additional cooling when the athlete must be transported for additional medical treatment.
We measured rectal temperatures in this study for the practical ease and validity of measuring core temperature. However, it is likely that core temperature was changing more rapidly in the 2 water-immersion therapies than we could measure with the rectal temperature, given that rectal temperatures usually lag behind true core temperatures by about 10 minutes.24
This would explain why we did not find a statistical difference in cooling rates between the immersion therapies and the mock immersion after 8 minutes.
There are several possible explanations for why ice-water immersion and cold-water immersion did not lead to different cooling rates. The 2 temperatures (5° and 14°C) may have been too similar to cause a physiologic difference in cooling rates. Another explanation is an alteration in the magnitude of peripheral vasoconstriction between the 2 modes of cooling. The vasoconstriction was not enough to interfere with body cooling; although the peripheral vasoconstriction may have been different between the water-immersion groups, it was not enough to alter the cooling rates.13
Consistent with the data regarding cooling rates, the immersion therapies led to lower Tre than mock immersion at the completion of immersion and throughout the postimmersion period (Figure ). Also, ice-water immersion induced lower Tre than cold-water immersion at 6 and 10 minutes postimmersion. Ice-water immersion stimulated a greater cooling rate after removal from the immersion bath, but this was negated by 15 minutes postimmersion. It is critical to note that these rectal temperatures do not translate into different cooling rates between ice-water immersion and cold-water immersion, due partly to the slightly higher (although not significantly different) preimmersion rectal temperatures in the cold-water immersion treatment group.
The superior cooling rates for ice-water immersion and cold-water immersion may have significant practical implications for the athletic trainer. Body cooling is known to be advantageous in lowering rectal temperature, as we have shown immersion (at either 5° or 14°C) to be superior to no immersion. At the onset of immersion (less than 8 minutes), no significant differences among ice-water immersion, cold-water immersion, and mock immersion were found, yet there was a trend toward greater cooling rates with ice-water and cold-water immersion as compared with mock immersion. The known lag in rectal temperatures behind the actual core temperatures could have prevented significant differences from being found. Therefore, we recommend ice-water or cold-water immersion even when time is limited before the arrival of emergency medical service personnel.
Potential side effects of ice-water immersion and cold-water immersion, such as hypothermic overshoot, peripheral vasoconstriction hindering a cooling response, and cardiogenic shock, did not occur during our study. The absence of these side effects is consistent with previous findings using immersion to cool hundreds of hyperthermic individuals.5
In our study, cooling did continue after removal from the ice-water or cold-water immersion. Although this continued cooling restored rectal temperature more quickly, normal baseline measures were not overshot.
We acknowledge some limitations to this study. Even though we found no significant differences between the WBGT in the crossover design and the averages were similar for all 3 treatments, this was a field study and the same weather conditions were not present for each individual trial. In addition, the hyperthermia of our subjects was of a limited nature compared with that normally found in exertional heatstroke patients. In future endeavors, we intend to compare the effects of ice-water and cold-water immersion on cooling rates of exertional heat stroke patients from a large-scale event, so as to not have to extrapolate our findings. We also aim to compare cooling rates via different modes in a controlled laboratory environment. Additionally, examining what effect movement of the water has during immersion therapy may be important because it may increase cooling rates.
Based on this study, we suggest using either ice-water or cold-water immersion when treating hyperthermic athletes. When an immersion tub is not available, alternative measures of cooling (cold-wet towels, ice packs, evaporative cooling) should be used until medical assistance arrives.