Olympian wearing an AIS ice jacket

Hot or humid environmental conditions have a negative effect on endurance performance (e.g., Galloway and Maughan, 1997). Any strategies that delay or reduce the increase in body temperature during exercise are therefore likely to enhance performance in the heat. In this article we summarize research on the effectiveness of one of these strategies, pre-event cooling. We also discuss a series of studies completed at the Australian Institute of Sport (AIS) that led to the development of a cooling jacket subsequently used by many Australian Olympians during the 1996 Summer Olympic Games in Atlanta.

Research on Pre-cooling

The concept of reducing skin or core temperature prior to endurance competition has been investigated since the early 1980s (see review by Booth et al., 1997). Lower skin temperatures enable a greater temperature gradient for dissipating heat from deeper regions of the body (Schmidt et al., 1981). Cooler skin temperatures mean that less of the total cardiac output is directed toward the skin, possibly allowing more blood to be directed to active skeletal muscle. Lower skin and core temperatures can also delay the onset of sweating and decrease sweat rate, resulting in a conservation of body water during a prolonged competitive event (Hessermer et al., 1984). The following published papers form the basis for the current pre-cooling practices used by athletes prior to competition in the heat.

Schmidt and Brück (1981) decreased core temperature by 1ºC in 12 well-trained rowers and observed that the heart rate and sweat rate response to a progressive maximal test was reduced in the pre-cooled versus the control trial. In this study all subjects rested at 28ºC for 30 min prior to the bicycle test that was performed at 18ºC. Pre-cooling did not affect maximum oxygen uptake (VO2max) or peak power output.

Hessermer et al. (1984) used a similar design but incorporated a 60-min maximal cycling time trial for their performance test. The eight well-trained rowers improved their average power output by 6.8% when the 60-min time trial was preceded by a cold air pre-cooling maneuver that decreased mean skin temperature by 4.5ºC.

Myler, Hahn & Tumilty (1989) investigated the effects of pre-cooling on the ability of rowers to perform at 30ºC and 30% humidity. They found that performance of a 6-min maximal rowing effort improved significantly: after 5 min of icing the skin, the rowers traveled 17 meters further in a 6-min all-out rowing test. The increase in power output averaged ~3%.

Lee and Haymes (1995) observed improvements in running performance following a pre-cooling procedure. Fourteen physically fit male runners were pre-cooled for 30 min using cold air. After a 10-min transition period, during which skin temperatures were allowed to warm, subjects ran until exhaustion at 82% VO2max at 24°C. Pre-cooling caused a 0.37°C drop in core temperature and an improvement in running time from 22.4 to 26.2 min, or 17%. (equivalent to about 1% in an event). The improved performance was associated with a decreased sweat rate.

Booth et al. (1997) cooled their subjects by about 0.5ºC using a 20-min cold-water bath. In a subsequent 30-min maximal running test in hot humid conditions (32ºC, 62% humidity), maximal 30-min run distance increased by about 2%.

Development of AIS Ice Jackets

Impressed by the potential benefits of pre-cooling on performance, scientists at the Australian Institute of Sport designed a cooling jacket for their athletes. The jacket was made from wet-suit material (Neoprene) and was designed to be packed with ice. In 1996 six women cyclists who were members of the Australian National road cycling squad agreed to use the prototype prior to a 25-km individual time trial held in Queensland, Australia. Not surprisingly, the cyclists felt noticeably cooler and upper chest skin temperature was reduced immediately following removal of the jacket. After the race the cyclists documented their impressions of the ice jacket by completing a questionnaire. Their suggestions were used to modify the jacket for the next prototype.

In collaboration with the Commonwealth Scientific and Industrial Research Organization and the University of Sydney, the AIS next recruited nine recreational cyclists to complete maximal graded exercise tests on a bicycle ergometer in a heat chamber at 32ºC and 60% humidity. The first trial was used to familiarize the subjects to the testing procedure. Subjects then completed either a cooling trial or a control trial in a cross-over fashion. For the cooling trial the modified cooling jacket was worn for the first 9 min of the protocol (125-175 watts). Subjects cycled for an average of 1.1 min longer during the cooling trial (332 vs 341 watts). Thermocouples attached to the mid-chest and the mid-back indicated that the skin temperature beneath the cooling jacket decreased from 32-35ºC down to 10-16ºC by the end of the 9-min period. During the cooling trial perception of effort and perception of thermal comfort was significantly improved. Despite these differences in perceptions and skin temperature, the ice jacket did not affect rectal temperature, heart rate, or blood lactate (Smith et al., 1997).

For the next study, four female and seven male rowers from the Australian Defense Force Academy completed two maximal 2000-m laboratory trials on a Concept IIb rowing ergometer in the AIS environmental chamber (33ºC, 60% humidity). Prior to the 2000-m trials, rowers consumed 350 ml of water and completed a 30-min warm-up at 75% of the power output achieved during a maximal effort familiarization trial. Prior to the start of the maximal exercise, an extra 150 ml of water was consumed. For the pre-cooling trial, a final version Neoprene cooling jacket developed by Neptune Wetsuits was worn throughout the warm-up period and the rowers were informed they were drinking water. For the placebo trial red food coloring was added to the water and rowers were told they were receiving glycerol, an agent that could aid in hydration and improve performance. Following pre-cooling, average rowing times decreased by 2.8 seconds, or 1.2%. In the cooling jacket trial there was less of an increase in core temperature and lower sweat rates during the warm-up. Following the warm-up period, rowers rated their thermal comfort significantly better in the pre-cooling trial, and this improved thermal comfort was also apparent following the 2000-m rowing test. Similarly, the perceived exertion following the rowing test was significantly lower, despite an elevated post exercise blood lactate and a lower blood pH.

The success of pre-cooling suggests that the duration and the intensity of a warm-up should be limited so that core temperature is not elevated prior to competition. One of the primary advantages of a cooling jacket may be that this form of active cooling allows an athlete to experience competition-specific exercise intensity during the warm-up without causing a substantial increase in core temperature.

AIS Jackets at the 1996 Olympics

Feedback from coaches, athletes and sport scientists was incorporated into the Olympic version of the cooling jacket for Australian athletes. It was left up to each sport to evaluate rules to ensure that the ice jacket would not be considered illegal prior to Olympic competition. The proper contacts were made and both Adidas (official Olympic clothing sponsor for Australia) and the Australian Olympic Committee agreed to support the use of the ice jacket by Australian Olympians. Once the administrative aspects of the project were in order Olympic ice jackets were sent out to track cycling, mountain cycling, road cycling, rowing, canoeing, hockey, and track and field. Each sport then refined the pre-cooling protocols for use prior to Olympic competition.

Approximately 200 green and gold ice jackets bearing the Australian coat of arms were produced for Olympic athletes traveling to Atlanta. Another 30-40 jackets were produced for Australian athletes competing in the Para-Olympic Games. In all cases athletes were not forced to use the ice jackets. Instead, athletes were made aware of laboratory data indicating the potential for beneficial effects and then the use of ice jackets was incorporated into practice sessions. Quite simply, many athletes liked the way the jackets felt when training and competing in hot conditions.

Evaluation sheets were returned by 43 Olympic athletes and 7 Olympic coaches who used the cooling jackets in Atlanta. Athletes and coaches represented road cycling, mountain cycling, rowing, field hockey, and track and field (mostly race walkers). Preliminary data indicate that 90% of the respondents used the cooling jackets during training sessions and 80% used the cooling jackets as an aid during Olympic competition. All athletes who used a cooling jacket during competition indicated that it made a positive contribution to their performance. Taking into account these comments and previous research, we believe that the jackets enhanced the output power of our athletes by at least a percent or two, depending on the event and the extent of pre-cooling. Ice jackets will be used increasingly in competitions held under hot conditions.

Australian rowing team wearing jackets at Atlanta in 1996

References

Booth, J., Marino, F. & Ward, J.J. (1997). Improved running performance in hot humid conditions following whole body pre-cooling. Medicine and Science in Sports and Exercise, 29, 943-949.

Galloway, S.D.R. & Maughan, R.J. (1997). Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man. Medicine and Science in Sports and Exercise, 29, 1240-1249.

Hessermer, V., Langusch, D., Brück, K., Bödeker, R.H. & Breidenbach, T. (1984). Effect of slightly lowered body temperatures on endurance performance in humans. Journal of Applied Physiology, 57, 1731-1737.

Lee, D.T. & Haymes, E.M. (1995 ). Exercise duration and thermoregulation responses following whole body precooling. Journal of Applied Physiology, 79, 1971-1976.

Myler, G.R., Hahn, A.G., & Tumilty, D.M. (1989). The effect of preliminary skin cooling on performance of rowers in hot conditions. Excel, 6,17-21.

Schmidt, V., & Brück, K. (1981). Effect of a pre-cooling maneuver on body temperature and exercise performance. Journal of Applied Physiology, 50, 772-778.

Smith, J. A., Yate, K., Lee, H., Thompon, M.W., Holcombe, B.V., & Martin, D.T. (1997). Pre-cooling improves cycling performance in hot/humid conditions. Medicine and Science in Sports and Exercise, 29(5), S263 (Abstract).