perform at your best in the summer heat with Pre-Cooling

Something that undoubtedly lowers athletes' performance, regardless of the sport, is heat, which we have previously discussed. When the temperature starts creeping above 18 degrees, many of us feel extra tired. If you're competing during the summer months, Pre-Cooling, meaning lowering your body's temperature before starting, can be a remarkably simple and effective trick to increase your margin until the level where high body temperature starts affecting performance. The main question is when pre-cooling works best, how significant the effect usually is, and which methods are most practical. The conclusion is that pre-cooling generally helps more as it gets warmer and the more intense your effort, with simple solutions like cold drinks or slushes often being both effective and practical. So now let's dive in!

We reviewed two articles from 2012: a Meta-Analysis from Germany (27 studies, totaling 269 participants) and a systematic review from England (13 studies).

We emphasize the meta-analysis as it included “performance” as a criterion. Participants were endurance athletes primarily involved in running, cycling, and triathlon. The studies used a cross-over design, meaning each participant served as their own control; all studies were independently reviewed.

The participants were split into two groups: those with 55–65 ml/kg/min oxygen uptake and those above 65 ml/kg/min. All were well-trained to very well-trained, but none were official professionals or elite athletes (such participants were excluded). Now you know who was studied and whether the results apply to you.

Our reduced performance in heat is due to several factors. On one hand, local effects like altered fluid volumes and reduced blood flow. On the other hand, enzymes that regulate energy metabolism are heat-sensitive and function less efficiently at higher temperatures.

Perhaps most importantly is central fatigue: our central nervous system is affected early on in the heat. Studies indicate that the brain slows down signals to the muscles so they can't work as hard, for example at 40 degrees compared to 18 degrees. If researchers electrically stimulate the muscles, they can contract more forcefully — demonstrating that the local capacity exists, but the brain sets the limit sooner.

Pre-Cooling involves using external aids to lower the body's core temperature before starting, giving the athlete more leeway before overheating hampers performance. By starting cooler, you can store more heat (what research calls "heat storage capacity") before the body reaches dangerous levels – allowing you to maintain high intensity longer and perform better.

In two studies in the review, participants reached a higher body temperature at exhaustion after Pre-Cooling compared to the control groups. Researchers suggest this might be because athletes could generate more heat since they performed better. The allowed increase in intensity (and therefore performance) might be due to either the brain being cooled and not putting a stop, or the afferent (sensory) nerve pathways sending signals that the body is still cool, like "Hey brain, it’s cool down here, keep pushing".

A little side note: nerve signals travel from the body's local areas via the spinal cord up to the brain. There are stories of pro cyclists using ice-filled mesh socks along the spine to influence thermal signals before they ascend to the brain. Elite athletes are, as you know, inventive 😉.

The performance increase across all studies in the meta-analysis averaged +4.9%. Various types of tests were used:

• Highest effect (+8.6%) in open-ended tests (continue until exhaustion at a given speed).
• In time trials and incremental tests (e.g., maximal oxygen uptake – VO2max – to exhaustion), the increase was 4.4–6.0%.

The benefit of Pre-Cooling also depends on how much heat you generate yourself. If you walk calmly, you won't see any effect. But if you push yourself hard — and can produce a lot of energy and thus heat — there's a lot to gain. The highest effect was seen in individuals with a VO2max over 65 ml/kg/min: on average, 7.7% better. Those with 55–65 ml/kg/min performed on average 3.8% better. Interestingly, this is the opposite of many other interventions where recreational athletes often gain the most; here, it's advantageous to be really well-trained, as you can generate more heat and thus benefit more from starting cold.