All physical activity conducted by human beings will also contribute to the increase of core body temperature which demands a lot of energy. Indeed, when the heat stock of the body is positive, i.e. when the heat production is greater than the heat loss, then the autonomic response of the body will be to re-allocate the energy of the body from the physical effort to the cooling down mechanism to stabilize the core body temperature and coordinate the inflow and outflows of energy.
Influence of cooling on performance in sports
In performance or individual sports, athletes often end up battling for the couple of seconds or milliseconds to overtake the opponent and win the race. In hot environments, that means that keeping the optimal core body temperature is often challenging. However, the impact it has on performance depends mainly on the type of sports.
For shorter and more explosive efforts such as in sprints, warm environmental temperature (>25°C) does not impair performance as much as for longer endurance sports, since it helps the muscle to stay warm and enhances muscle contractile properties. On the contrary, an analysis of Guy et al. of top performances in endurance events pointed out that athletes performed in average 2% better in temperature conditions (<25°C) than in warm ones (>25°C) and the longer the distance, the greater the impairment.
The impairment of performance due to hyperthermia (heat) is generally acknowledged in performance sports and despite the little amount of data on the use of cooling strategies in elite sports, a study from Périard et al. disclosed that 52% athletes surveyed before the 2015 IAAF World Championships planned to use at least one of those mechanisms.
Different types of cooling strategies
Cooling strategies could be separated into two categories, internal and external. Both approaches differ their consequences, since the former activates central thermosensors and the latter, the peripheral ones. But they are complementary and are often used in collaboration for optimal outputs.
Internal cooling refers mostly to the indigestion of cold/ ice beverages and is often used prior exercise/ performance. Ice, because of its solid form, will have up to 2x the effects of cold-water ingestion. Both will act as a heat sink, i.e. will absorb all additional heat created through warming up. Additionally, it will suppress the activation of sweat glands independently of changes in skin or core body temperature, leading to lower sweat rates and lower evaporation heat loss from the skin. The following video, recorded during the Tour of California, shows how coaches and riders use drinking as common internal cooling mechanism.
However, this cooling strategy has a downturn: it may just delay the onset of sweating and/or the vasodilation and may in turn increase the rate of heat storage during the early stages of exercise. Moreover, the effects are disproportionally high on thermal perception than on actual body temperature.
External cooling in turn, has many more options. They mainly serve to decrease tissue temperature, yet its efficiency and strategic use vary:
- Cold water immersion is often used post- exercise for treating hyperthermia and is well known to help in the recovery process. However, it is strongly discouraged before exercise: the consequential reduction in muscle temperature reduces maximal power, force and velocity.
- Cooling vests or ice socks placed in the neck aims at cooling the body through direct and conductive and evaporative methods. Cooling vests typically covers approximately 25% of the body surface but cools only 5-10% of the body. Often used as a pre-cooling routine, such ice vest reduces skin and core body temperature, slow down the heart rate, influence the perception of task difficulty and improve thermal comfort. For a nice explanation of how a cooling vest looks like, check the video below.
Timing of cooling strategies
Cooling strategies could be used at different times, either before, during or after the race, depending on the purpose:
- Pre-cooling strategies mostly aim at creating a heat sink to increase the heating capacity of the athlete during the race. The challenge is to achieve this while keeping the muscle warm enough to quickly reach their maximal performance rate. Another risk related to the pre-cooling strategy is the “after drop”, i.e. when the cooling is too severe, then vasoconstriction of the peripheral blood vessels occurs which in turn delays the transfer of the cooling of the skin to the core. The pre-cooling effects do not always last to the race if the cooling is insufficient or if the starting pace is too high.
- Cooling may also occur during performance, which is referred to as per-cooling strategies. It has generally been acknowledged that cooling may improve performance and capacity in the heat. However, because of the practical complications it uses has been often restricted. The internal cooling has not been much investigated in comparison but showed very promising results, with up to 13% of improved cycling capacity after the ingestion of cold (4°C) water. Yet, other studies have also pointed out the risks related to the indigestion of ice-slurries, especially for young athletes.
- Post-cooling strategies also are central in dealing with overheating and its potentially harmful consequences. It may help for recovery and hence participate to improving future performance.
In the following video, some coaches at the Vuelta de España (where usually temperatures get really high) explains how they combine cooling strategies, either internal or external, to keep their riders' core body temperature as low as possible (spoiler: it is a combination of drinking, electrolytes and ice socks during the race, with some rest and cooling at the end).
The best approach for cooling always will depend on many factors, such as the athlete's acclimatization, humidity levels, outside temperature, and the kind of competition. That is why cooling needs a personalized plan to get the best results. Indeed, creating that plan requires on-time core body temperature monitoring. Curious about this topic? Contact us for more information.