Maximising your performance in the heat
It is commonly known that for most athletes performance significantly declines in extreme heat, but what less common is how athletes can effectively avoid these steep declines in performance by preparing adequately for the heat.
First and foremost, we must address the key differences between heat acclimation and heat acclimatisation. The first being artificial heat exposures with the intentions of raising the core body temperature to stimulate adaptation, and the latter being a natural adaptation to heat exposure over time. In this blog we will focus on heat acclimation as most (especially us in the UK) don’t get enough natural heat exposure to allow for adaptations.
The athletes thermal environment is responsible for their thermoregulation and therefore performance in the heat. Metabolic production, sweat evaporation, radiation and convection are some factors that affect this. A conceptual heat balance equation can be used to determine the rate of heat storage: rate of heat production +/- rate of total heat loss/gain = rate of heat storage.
An excessive rate of heat storage is shown to influence cardiovascular performance by altering muscle metabolism, leading to;
Reduction in skeletal muscle blood flow
Fiber type recruitment
Increase in muscle temperature
The goal of heat acclimation is to reduce the effect of these factors when an athlete has to perform in extreme heat, however an individual’s performance is highly dependent on their ability level. For example, recreational marathon runners have shown to have a performance decrement of up to 12% at 25 Degrees Celsius, however in elite marathon runners this can be expected to be only 2-3%.
There are 3 different approaches to heat acclimation;
Short-term heat acclimation (STHA)
Medium-term heat acclimation (MTHA)
Long-term heat acclimation (LTHA)
Any of these approaches are a chronic heat-alleviating intervention which is designed to have longer lasting affects than an acute intervention. Chronic interventions are ideal to be done in preparation for a goal event that is likely to be performed in extreme heat. STHA is the preferred approach of top endurance athletes, allowing for the acclimation protocol to have minimal affect on the athletes usual training stimulus, and holds less risk of the athlete overreaching.
There are differing techniques used when applying STHA, one being controlling the intensity/work rate and environment of an athlete during exercise in order to raise their core body temperature to above 38.5°C for an extended period of time. Another being a more passive technique involving just controlling the athletes environment in order to raise their core body temperature above 38.5°C, this could be through a sauna or heat chamber. 38.5°C has shown to be the core body temperature that is both necessary to create adaptation, yet low enough to be safe.
So what does the research suggest when it comes to creating an effective STHA protocol? It has been shown that the benefits of STHA can be held onto for two weeks post acclimation, however as time progresses through this period the adaptations will diminish without any further heat exposure. It is suggested that a STHA is completed whilst the athlete is in the taper phase of training towards a goal event, usually around one to two weeks out from the event. During this period training load is lower allowing space for a carefully planned heat acclimation without overloading the athlete, which would push them towards overreaching having a negative affect on performance. The recommended volume of heat exposure during the STHA is 60 minutes per day for 5-7 days above a core temperature of 38.5°C. The full 60 minutes may not be possible for the athlete in the first few days, so they should get as close as they safely can and build up to the 60 minutes. Passive techniques have shown to be more effective than active techniques in the athletes taper phase, as they create the same adaptations from the heat exposure without creating any additional muscular strain. This could be through the use of a sauna, a hot bath or an environmental chamber if the athlete can get access to one. The specific technique is not important, rather ensuring the body is exposed to a core temperature above 38.5°C.
Proven benefits of SHTA:
Increase in blood plasma volume
Decreased core body temperature
Improved peak power in the heat
Improved whole body heat loss
Improved self-paced time trial speed in the heat
Cooling strategies
For some it will be the case that heat acclimation is just not a viable option, so what is the best course of action to mitigate the effects of the heat on race day? There are plenty of recommended cooling strategies available, however when it comes to ultra distance events these should not be applied due to the risk of masking the onset of heat illness. If this is not a risk for a given event then useful cooling strategies could be pre-cooling through an ice bath or ice vest, or during an event through the ingestion of ice slurries or menthol based products. These are temporary fixes to bring the core temperature down giving it further to rise before performance is affected.
References
Garrett, A.T., Creasy, R., Rehrer, N., Patterson, M., Cotter, J. (2012) Effectiveness of short-term heat acclimation for highly trained athletes. Euro Journal of Applied Physiology, Vol 112 (5), pp.1827-1838.
Febbraio, M. A., Snow, R. J., Stathis,C. G., Hargreaves, M., Carey, M. F. (1994) Effect of heat stress on muscle energy metabolism during exercise. Journal of Applied Physiology, Vol 77 (6), pp.2827-2831.
Reeve, T., Gordon, R., Laursen, P., Lee, J., Tyler, C., (2019) Impairment of Cycling Capacity in the Heat in Well-Trained Endurance Athletes After High-Intensity Short-Term Heat Acclimation. Journal of Sports Physiology and Performance, 14(8), pp1058.
Howe, A.S. and Boden, B.P. (2007) ‘Heat-Related Illness in Athletes’, American Journal of Sports Medicine, 35(8), pp. 1384–1395.
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