Cooling Vests & Performance: Superhuman Effort in the Heat
Operating in extreme thermal conditions
Humans can only operate above a normal body core temperature of 98.6oF for limited periods of time. Due to this biological limit, extending working effort under extreme thermal conditions has an obvious physiological component. If not mitigated, uncontrolled rise in core temperature doesn’t just impair our ability to work- it can be deadly. Along with other factors, heat stroke is clinically defined as a body core temperature exceeding 104oF, although it can occur at lower temperature. Less severe (and more frequently experienced) heat exhaustion or heat cramps often mark the point where a person can no longer maintain a working effort. Recovering from heat illnesses requires a cooling off period before resuming any effort and, in the case of heat stroke, rapid cooling can make the difference between life and death.
Exceeding Our Natural Limits
In study after study, cooling vests have been proven to extend the amount of time a person can sustain working effort in hot conditions. The magnitude of increase depends on the intensity of the working effort. No one can hold an all-out sprint as long as a slow jog; similarly, cooling vests extend working periods proportionately longer during lower intensity efforts. That said, cooling vests also extend working duration even during highly intense efforts and for individuals wearing thermally restrictive protective equipment. On average, research demonstrates ice-based cooling vests like Qore Performance products consistently improve human performance (e.g., increase time to exhaustion) by nearly 20%, and occasionally much more.
Light Working Efforts
Cooling vests most significantly increased the time subjects can sustain working efforts during research protocols with relatively lighter physical demands. Studies demonstrate working effort can be sustained up to, and sometime more than, 100% longer when subjects wear a cooling vest. For example, one study required subjects to wear standard work uniform while completing a series of walk-rest cycles over 6 hours under various thermal conditions. During the 135oF test, subjects wearing cooling vests were able to work an average of 1.5 hours longer than those without a cooling vest, more than doubling their tolerance time.
A different study by the Naval Health Research Center came to a similar conclusion. Subjects wore an ice vest similar to a two-plate Qore Performance ICEPLATE® system during a relatively light working effort of walking on a treadmill for 20 minutes, followed by a 40 minute break, repeated for six hours. During the hottest experiential conditions (~135oF), male subjects lasted an average of just 88 minutes without a cooling vest, and female subjects 71 minutes. Repeated wearing cooling vests, male subjects lasted 242 minutes, and female subjects 168 minutes- an amazing increase of 175% and 136%, respectively!
The ability to work longer when wearing a cooling vest is due in large part to the reduced rate of body core temperature rises; cooling vests provide a heat sink to dump metabolic heat, assisting the body’s physiological ability to thermoregulate. This effect was demonstrated in a third study published in the Journal of Thermal Biology. Subjects performed relatively light walking efforts in a heat chamber. Measured using a small thermometer ingested prior to the study (a device that continuously transmits core temperature from the stomach), subjects wearing cooling vests had core temperature increases of approximately 1oF at the end of a 2.5-hour test. Without cooling vests, core temperature increase was closer to 2.5oF.
As we’ve explored in prior posts, humans can only survive when core temperature remains in a relatively narrow window centered around 98.6oF, so the ~1.5oF reduction in temperature achieved by wearing a cooling vest, though seemingly small, is physiologically significant. Given the significant increased work duration observed during lighter efforts under hot conditions, a Canadian Defence Research and Development technical report concluded ideal military situations for wearing cooling vests may be “light work” activities like manning a 50-calibre machine gun.
Above: When body armor is worn, ICEPLATE® is mounted internally using IMS Pro Gen 3, shown here, to provide passive cooling. IMS Versa Gen 3 may also be used for similar integration.
Heavy Working Efforts
While it is clear tolerance times are extended during light working efforts, research also consistently demonstrates the positive effects of wearing a cooling vest during heavy work. Based on theoretical calculations, the same Canadian report estimates wearing cooling vests results in a 20-30% improvement in tolerance times during physical effort the U.S. military classifies as “moderate” to “hard” work. Human subjects testing backs up this theoretical finding, as we’ll now discuss.
Cooling vest studies at the extreme edge of human thermal tolerance often focus on the effect vests have on subjects wearing firefighting, bomb disposal, and chemical suits. In all three scenarios, the required protective equipment is heavy, bulky, and thermally restrictive. Working while wearing such equipment requires greater metabolic effort, increasing thermal stress on the subject while preventing metabolic heat from readily transferring to the environment. In hot environments, such combination puts the operator at elevated risk of heat stroke. During extremely strenuous work under restrictive protective equipment, using a cooling vest can extend tolerance times by 10-20%.
One study of firefighters quantified the performance increase achieved when wearing an ice vest that also allowed the subject to drink as the liquid melted. (The study used frozen sport drink, but in practice the tested equipment is conceptually identical to a Qore Performance ICEPLATE® system with drink tube). The scientists concluded the combined effect of cooling and hydration “synergistically manifested” in lower core temperature, skin temperature, and heart rate, and better thermal sensation (i.e., comfort) following testing. As a bonus, the weight carried by test subjects decreased as fluid was consumed. For obvious reasons, the ability to drink during heavy working efforts reduces thirst sensation, important when concentration is required during dangerous tasks like firefighting.
Explosive ordinance disposal (EOD) suits are another example of bulk, heavy, and thermally restrictive protective gear. Such combination can quickly cause EOD technicians to overheat and fatigue in hot environments. One novel study evaluated if performance increased by wearing an ice-based cooling vest under EOD suits. The test protocol was brutal- walking at a moderate pace in a bomb disposal suit for up to one hour in hot, humid conditions (95oF temperature and 50% relative humidity). For safety reasons, testing was stopped when a subject’s heart rate exceeded 90% of maximum value.
None of the eight participants could complete the test protocol without an ice vest. Even with an ice vest, only a single subject was able to complete a full 60-minute test. However, all subjects performed longer when wearing the cooling vest under their EOD suit, with an average increased working time of 8 minutes (an ~27% increase). Such modest increase in work duration can have a significant impact during high-pressure tasks like bomb disposal.
Other research substantiates this finding. A study conducted at 104oF, and which allowed EOD operators to swap out melted phase change vests for fresh, frozen ones, found subject’s core temperature over 1oF lower at completion of a series of physically demanding tasks. Even without exchanging melted vests for fresh ones, core temperature was still about 0.8oF lower compared to control testing without the cooling vest. The findings are likely conservative because the type of cooling vests studied incorporated a phase change material that melted at about 77oF. Such design typically has much less “cooling power” than ice-based systems like those manufactured by Qore Performance. It is probable that using an ice-based vest would result in even lower core temperature rise.
For thermoregulation, chemical suits represent the worst possible scenario. By design, there is no air exchange between an operator encapsulated in such equipment and the (potentially lethal or toxic) outside environment. This creates conditions where the primary human thermoregulatory mechanisms – sweat evaporation and convective cooling – are quickly negated. In addition, operators wearing chemical suits often must perform physical tasks such as decontaminating equipment or responding to hazardous material spills, increasing the metabolic waste heat generated. The operator is essentially trapped in the suit with their metabolic waste heat.
Given the danger of heat stroke when wearing chemical suits, a number of studies have attempted to find methods to cool the operator, including studying the effect of cooling vests worn under chemical suites. Results indicate work time can be improved by wearing cooling vests, but given the extreme heat burden, improvements are typically marginal. One study found subjects performing heavy work under chemical suit lasted an average of about 5 minutes longer when wearing ice-based cooling vests.
A less physically demanding study, using a phase change material that melts at 65oF (i.e., less cooling power than ice), found soldiers wearing chemical suits could walk at a fast pace an average of ~28% longer (or an additional 10 minutes) compared to subjects without cooling vests. A similar study using an ice-based vest found working time increased by about 12 minutes compared to the no-vest control test. Critically, only 4 of ten subjects completed the full test protocol without the cooling vest, while all but one was able to last the full two-hour duration when wearing the vest.
Other Working Efforts
Cooling vest use pops up in some surprising places, such as Formula 1 racing. Starting this year, drivers have the option to wear a cooling vest (albeit one recirculating chilled water, practical only in fixed locations like race cars and aircraft) to combat high temperatures that have incapacitated drivers, such as Lance Stroll who “passed out” racing in hot Qatar. The F1 cooling vest system is expected to become mandatory starting in 2026.
In some occupations, employees might have limited rest periods between working effort. For example, baggage handlers at airports move between bouts of physical labor on a hot tarmac and recovery periods waiting for the next arrival or departure. One particularly extreme example is a study conducted on Australian firefighters. Assuming firefighters may be tasked to reenter a fire scene after minimal recovery, the study protocol included two twenty-minute sessions of simulated rescue searching in a 220oF chamber separated by ten minutes of rest.
In the firefighter subjects, core temperature continued to rise even during the brief ten-minute rest period, and, unsurprisingly, rose higher during the second round in the heat chamber. The increased core temperature resulted in body temperatures approaching occupational safety limits and noted significant reductions in grip strength after the second 20-minute round. Researchers concluded that passive cooling methods (i.e., resting) alone was ineffective at reducing core temperature rise and longer recovery periods, or active cooling methods, should be used during the brief recovery period.
Active cooling methods like wearing a cooling vest during rest periods have benefits beyond firefighting. For example, athletes such as soccer players have fifteen minutes to recover during half time and can’t wear cooling vests during competition. A study of athlete recovery found using a cooling vest immediately after exercise significantly reduce body heat storage during the first fifteen minutes of rest. The reduction was significant; 46% of total measured reduction in body temperature was achieved during the first fifteen minutes when wearing a cooling vest, compared to just 36% in the control group. Similar beneficial findings were observed for heart rate, skin temperature, and thermal sensation.
Conclusion
Cooling vests are proven to extend work tolerance times in hot conditions regardless of the activity performed. The magnitude of increase depends on the task, but even limited wear of active cooling systems during rest breaks results in physiological improvement. Systems like those marketed by Qore Performance allow users to achieve superhuman efforts by extended tolerance even during heavy exertional efforts!
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About the author: Dr. Erik Patton holds a PhD from Duke University where he conducted research on the challenges rising temperatures pose for military training. An Army veteran, Erik has served in a variety of extreme climates ranging from deserts in the U.S. Southwest and Middle East (+120oF) to Arctic conditions in central Alaska (-42oF).