Increase performance exponentially by cooling down faster

Fitness is vital for sports performance, with athletes expected to maintain optimal output in all weather conditions, times of day, and environments. However, one may notice that they cannot continue to exert physical effort forever. Whether muscles stop contracting when doing pushups or cannot support any more running, it is as if one’s muscles reach a threshold that inhibits further work.

Indeed, this is the case because the body contains internal mechanisms that prevent overheating. In “Supercharge Exercise Performance & Recovery with Cooling,” Andrew Huberman, a Professor of Neuroscience at Stanford School of Medicine for over 20 years, explains that continuing to exert physical effort against the body’s reflex to stop can lead to hyperthermia and death. Overheating is so substantial that temperature-increasing performance drugs such as clenbuterol are banned from the Olympics due to its induced fatalities among athletes.

Studies show an increase in performance after proper cooling

The main thing humans do to prevent overheating is to stop. Huberman continues, stating that this is a subconscious effect caused by the connection between willpower and the temperature of muscles. This is why on a hot, humid day, one may notice experiencing fatigue and an inability to put forth more effort rather than on a colder day because the body is heating up at a faster rate in the warmer weather. In practice, thermoregulatory researchers at Stanford University Dennis Grahn and Craig Heller measured that having even a 0.6°C increase in muscle temperature resulted in a 17% change in the work volume capacity, or sets and reps total (see study below).

While this natural instinct to prevent bodily overheating cannot be bypassed, there is an optimal way to cool the body that can enhance physical performance exponentially. A multiple-part study published in the Journal of Strength and Conditioning Research demonstrated that proper cooling of the body lead to a 144% increase in resistance training capacity compared to no gain in the group that did not use the cooling method. Furthermore, Huberman describes another instance whereby using this cooling method has led a professional American football player from the 49ers team to triple performance output on the number of sets and reps of dips (a resistance exercise) in less than a week while holding the same increased performance without using that cooling method.

Despite the deficiency in studies regarding how this cooling method can be used in endurance training, it is more logical to evaluate resistance training because it is a more controlled way to increase the temperature of individual muscles or groups of muscles. Because these effects are physiological, this cooling can be applied to all muscle contractions, regardless of which type of muscular effort is done. Meaning, in endurance training like running, the muscles heat up more slowly than in resistance training (because the effort is distributed among the whole system); however, the ways the muscles heat up are the same. This means the success of this cooling method in resistance training will carry over to endurance training and other muscular work.

Temperature sensitivity in muscles

To understand how this cooling can be leveraged, it is first critical to understand the muscle physiology of how and why muscles stop contracting. The physiological reason why muscles stop contracting is not because they run out of energy, lack oxygen, or undergo a buildup of chemical waste. While these certainly impact muscle performance, the signal for a muscle to stop contracting, or fail, is when the temperature gets too high.

In the muscle, ATP is a form of energy that is utilized to generate muscle contraction. Through chemical processes, humans are able to convert the food they eat into ATP and then use it as fuel for every cell in the body. Any movement requires ATP; however, the range at which ATP can function and produce muscle contraction is very narrow. Huberman explains that a working muscle can generate heat extremely fast, and upon reaching 39 to 40°C, the enzymes responsible for generating ATP are denatured, and can no longer produce muscle contraction. In other words, the chemical processes responsible for using ATP in the muscle stop working when the temperature gets too high. This is an extremely narrow gap because resting body temperature is slightly less than 37°C; an increase of just 2 degrees means the muscle will not be able to contract anymore.

In particular, an enzyme involved in creating ATP that cannot be bypassed for muscular contraction is pyruvate kinase. Because pyruvate kinase stops functioning when reaching a higher temperature, keeping the muscle at a cooler temperature will result in producing more muscular work per unit of time. 

A special vasculature: AVAs

This leads to the question, what is the best way to cool the body? It turns out there are areas of skin on the body that allow for optimal heat transfer, that when exploited, can move more heat out of the body and cool the whole body more rapidly. These are the face, palms of the hands, and soles of the feet. What is characteristic about these regions is that they contain a very particular skin type and pattern of blood vessels. This is called glabrous skin, containing no hair and a vasculature pattern called AVAs.

A peer-reviewed paper published in the Journal Temperature describes that AVAs, or arterio-venous anastomoses, are a network of blood vessels found mainly in glabrous skin that allow more blood to pass through them per unit time. Normal skin that covers the rest of the body includes blood vessels that are less effective at passing heat out of the body. Normal blood vessels follow the pattern of arteries, larger oxygen-rich vessels that travel from the heart; to capillaries, microscopic vessels where oxygen is exchanged; to veins, oxygen-poor vessels that lead back to the heart.

Arteries → Capillaries → Veins

AVAs, however, bypass capillaries, creating a direct connection between arteries and veins. This direct connection facilitates a larger inner radius of the vessels that cannot be achieved between capillaries. This is significant because according to Poiseuille’s Law in physics, the amount of fluid traveling along a pipe will increase by the 4th power proportional to the radius. This means that by increasing the radius of blood vessels by a little bit, they can quadruple the amount of blood that flows through them. Therefore, more heat can travel out of the body through the palms of hands, soles of feet, and face because they include AVAs.

Palmer cooling methods

Palmer cooling is the exact technique used in the sports studies above by Grahn and Heller. In their case, they designed a “custom-built heat extraction device” that circulates 15-16°C water, which was then applied to the palms of the hands. Despite the really advanced technology in the lab setting, there are applicable methods that mimic such a cooling device and can be utilized by any athlete for free.

The two most practical are emerging the hands and feet into cold water or moving an ice pack or frozen water bottle between the hands. The first method would involve filling a sink or bucket with cold water, and after every set, submerging the hands and/or feet into the water for a few minutes (3 minutes in the study). Huberman describes that there is no set temperature of water at which every single individual cools off most effectively, which leaves some room for personal experimentation to discover the most optimal temperature; however, the water cannot be so cold that it promotes vasoconstriction. When it is hot outside, the blood vessels dilate to pass and dump more heat out of the body, but when it is cold, vessels constrict, reducing their size to avoid losing too much heat. If the subjects were to submerge their hands into freezing water, the ice would actually result in constriction of the blood vessels in the hands, which inhibits proper cooling.

Nevertheless, another palmer cooling method is passing a frozen object between two hands. Though ice causes vasoconstriction, because the ice pack or water bottle is being moved between the hands, it is only exposed for a few seconds at a time in each hand; therefore, it is not a complete submergence and still allows for effective cooling. It is possible to partially see the efficiency of the cooling because the palm will turn slightly red when more blood is being passed through it. Holding a frozen pack or water bottle is especially useful because it is portable and there is not always access to a sink or bucket with adjustable cold water temperature.

The future of palmer cooling lies in technologies such as sports cooling gloves and insoles, which can be worn in training to cool down, but also in-game to optimize muscular work per minute of time without overheating. This could not only be invaluable to individual and recreational performance but be utilized by professional teams and players to optimize performance. Athletes would be able to increase work output in each training session while having long-term gains in performance without using that cooling method.

Though palmer cooling is fundamental in sports, other occupations and services can leverage this cooling method. For example, firefighters, to avoid overheating may value technology to cool themselves while working in extremely hot settings. Likewise, medics can apply these principles to cool any hyperthermic patient. Converse to cooling the body, heating the body is also optimized through heating the body at these glabrous skin portals with AVAs. Patients experiencing hypothermia or simply being very cold can apply warmth to their palms, soles of feet, or face.