Cool it: use your head!

Can head cooling improve performance in the real world?

Although the research on head cooling for performance is persuasive, many of the cooling strategies are impractical for use in a competitive environment. For example, it would be difficult to run or cycle carrying a water spray bottle and waving a fan around in front of your face! In addition, some strategies involving repeated application of water or other solutions to the skin of the face or neck can result in skin irritation. However, a fascinating new study by a team of British scientists has looked at the effect of continuous head cooling on 5km running performance (the first ever study to investigate continuous head cooling)⁽²⁰⁾. 

Published in the International Journal of Exercise Science, this study looked at the use of a commercially available ice-filled ‘cooling cap’ worn on the head during treadmill running in a hot environment with an ambient temperature of 32C (90F). For the study, ten well trained triathletes from local triathlon clubs were recruited. Following an initial familiarization session, the triathletes undertook two separate trials in a random order on two separate days. Both trials involved the participants completing a 10-minute submaximal run followed by a 5km time-trial run in the heat (32C /90F). However the two trials differed as follows:

• An experimental trial, in which the participants wore a cooling cap for both the 10-minute submaximal run and the 5km time-trial. The cooling cap used in this trial was a commercially available product made by ‘ICED Cap’ of Norcross, USA (see figure 1). This consisted of a polyester fabric cap with a closable compartment, where around 300 grams of ice can be added to provide cooling to the top of the head.
• A control trial in which participants wore no cap.

In order to try not to introduce any placebo effect into the trial, the triathletes were told that the experiment was designed to investigate whether wearing a cooling cap helped (due to cooling) or hindered (due to weight) running performance. This ensured they had no expectations of a better performance in either of the two trials.

During the two trials, the triathletes’ core temperatures and heart rates were measured every minute of the submaximal run and every kilometre of the 5km time-trial run. Ratings of perceived exertion (RPE) were also measured, whilst whole body thermal comfort was recorded using a modified 10-point categorical scale where 1 = ‘extremely cold’, 5 = ‘comfortable’, and 10 = ‘extremely hot’. In addition, sweat losses were measured by the change in body mass pre to post exercise and the skin temperatures on the participants’ foreheads were also monitored. For both trials, participants were provided with water and told to drink freely, and received no physiological or verbal feedback during the time-trials. 

What they found

The key findings were as follows:

• When the cooling cap was worn, the triathletes experienced reduced forehead temperatures (figure 2) and improved thermal comfort (see figure 3).
• Most importantly, the 5km time trial times were faster when the cooling cap was worn, averaging 1,175 seconds with the cap compared to 1,189 seconds with no cooling cap (a performance gain of 1.2% - (see figure 4).
• No other variables such as core temperature differed between the cooling cap and control trials.

Figure 2: Forehead temperatures with and without cooling

^{Scale 0-10 = 10-minute sub-maximal run at 70% VO2max. Scale 1-5 = distance covered in subsequent 5km run. The forehead temperature was significantly lower at all points when the cooling cap was worn.}

Figure 3: Thermal comfort with and without cooling cap use

^{Higher numbers = more heat discomfort. Although heat discomfort rose in both trials, it was reduced at all points in the 5km time trial when the cooling cap was worn.}

Figure 4: 5km times with and without cooling

^{Columns show averaged times for the group as a whole. Dashed lines show the individual responses. Eight participants had faster times with the cooling cap and averaged out, the overall responses were significantly faster when wearing the cap.}

The authors noted that this was ‘the first study to observe that continuously cooling the head region with an ice-filled cap enhanced time-trial running performance by 1.2% in trained athletes’. They also noted that while a performance improvement of 1.2% with the cap may seem small, a 14-second reduction in 5km time at the typical running speeds was the equivalent of finishing a race 58 metres ahead compared to no cap, and that this type of performance gain is equivalent in magnitude to other strategies routinely adopted by endurance runners to improve performance, such as altitude training⁽²¹⁾, strength training⁽²²⁾, and the use of high intensity warm-up regimens⁽²³⁾.

Practical applications for runners and other athletes

Although the sample size used in this study was small, the results in favor of the cooling cap were statistically very significant. Bear in mind too that these gains were achieved with a weight penalty of around 300 grams placed on the head! How was it that performance and thermal comfort improved, even though there were no differences in core temperature? 

One possible explanation is that the performance-boosting effect of cooling the head region results from direct cooling of the cerebral blood and a subsequent reduction in brain temperature. That’s relevant because research suggests that brain temperature is a major determinant of exercise capacity⁽²⁴⁾, and therefore cooling the brain directly provides a real advantage. The lower forehead temperatures indicate that cerebral blood cooling was almost certainly taking place.

In terms of advice for athletes, these findings provide good evidence for the use of head cooling during exercise in hot conditions. The easiest way to achieve this is with the use of some kind of ice containing headwear such as the Iced Cap used in this study. Although Iced Cap is readily available in the US, readers in Europe and Australia/NZ and other parts of the world may have to look to other brands. Here in the UK for example, ice caps by Compressport are affordable and easily purchased online.

When using these devices, the obvious limitation is time. In hot weather (when they’re most useful), the relatively small amounts of ice used in these caps will melt within half an hour or so. This means that their use is more relevant to shorter races, or to the later stages of a longer race – if you have a special someone to prepare the cap and pass it to you at the appropriate time! They can of course be topped up with fresh ice but this takes time and could self defeating. 

To ensure that the cap can be loaded with really cold ice, the best strategy is to prepare the ice in the main freezer compartment (at -18C or lower) and then transfer it to a cold storage box just before you leave home. A good tip is to put much more than 300 grams of ice in the box; the greater the volume of ice, the lower the rate of warming because of the reduced surface area to volume ratio. It also gives you the option to top up your cooling cap if you are taking part in a longer event. Needless to say, when ice is placed in the cooling cap, it should be as near as possible to the start of your race!

^References

^{1. Med Sci Sports Exerc. 2006 Oct;38(10):1762-9 / 2. Med Sci Sports Exerc. 2006 Sep;38(9):1650-8 / 3. Med Sci Sports Exerc. 2007 Feb;39(2):323-9 / 4. Int J Sports Med. 2006 Oct;27(10):765-70 / 5. Int J Sports Physiol Perform. 2011 Jun;6(2):208-20 / 6. Int J Sports Med. 2008;29(10):812–816 / 7. Br J Sports Med. 2015;49(1):7–13 / 8. Int J Sports Med. 2014;35(10):840–846 / 9. Exp Physiol. 2006;91(5):925–933 / 10. J Sports Sci. 2013;31(12):1271–1279 / 11. Scand J Med Sci Sports. 2016;26(10):1209–1216 / 12. Can J Appl Physiol 2005;30(1):87–104 / 13. Eur J Sport Sci. 2011;11(6):419–429 / 14. Eur J Sport Sci. 2011;11(6):419–429 / 15. Sports Med. 2017;47(5):829–841 / 16. J Physiol. 2005;565(1):335–345 / 17. Physiol Res. 2008;57(6):863–872 / 18. J Sports Sci. 2017;35(8):798–805 / 19. J Sports Sci Med. 2017 Mar 1;16(1):77-83 / 20. Int J Exerc Sci. 2023; 16(6): 193–204 / 21. J Appl Physiol. 2001;91(3):1113–1120 / 22. Sports Med 2018;48(5):1117–1149 / 23. Int J Sports Physiol Perform. 2013;8:77–83 / 24. Exp Physiol. 2012;97(3):333–339}