The original article was published for the RunTriMag on June 8th, 2024. Access here: https://runtrimag.com/the-effects-of-heat/
The Effects of Heat on Performance
As summer approaches and temperatures rise, race season begins. Consequently, training in high temperatures often becomes challenging, making miles feel harder and causing heart rates to elevate even at slower paces, making it challenging to push harder. Is our performance declining? Are we getting slower? Don’t worry; you are not losing your fitness! Training in high temperatures is simply harder for the body and metabolically more demanding. In this article, I will explain what happens when we train and compete in the heat, its benefits, the associated risks, and how we can acclimatize to make this experience more manageable. These are the effects of heat.
Physiology of Heat Acclimatization
In my previous blog, published on my website, I explained in detail the physiological changes that occur during heat adaptation. Complete heat acclimatization lasts 10-14 days. During this period, the body undergoes a series of changes to handle heat stress, such as an initial increase in heart rate that decreases over 3-4 days, improving stroke volume and cardiac output. Sweat production rises, aiding in thermoregulation (the body’s ability to maintain core temperature), and plasma volume expands due to increased water retention. This stimulates increased haemoglobin mass, improving oxygen transport to muscles, which is thought to boost VO2max and lactate threshold. Heat stress also enhances anaerobic capacity and triggers heat-shock proteins, which are key for protecting cells from stress. Studies show that heat acclimatisation can improve overall performance, though some research has limitations.
Performance Effects
Optimal temperatures for running are typically between 5-10°C, being higher in females. When temperatures start increasing above this optimum, there is a significant drop in performance. In a study published by Helou and colleagues in PLOS ONE (2012), the performance of marathon finishers competing in six renowned marathons with different recorded temperatures showed a speed loss of 3.91% and 2.84% in males and females respectively when the temperature was over 10°C above this optimum temperature, and 17.73% and 12.43% in males and females respectively when the temperature was over 20°C of this peak temperature! Moreover, this decline is more pronounced with age and in less fit athletes. This is due to heat raising core body temperature and straining the cardiovascular system. The body prioritises heat dissipation over oxygen delivery to muscles, slowing pace and increasing perceived effort. High humidity further exacerbates this by hindering sweat evaporation, which impairs cooling.
Health Risks
Due to the increase in sweat, there is a higher risk of dehydration. Interestingly, women generally have lower sweat rates than men due to a larger number of glands that make less sweat per gland. In the heat, we can lose more than one litter of sweat per hour, and this needs to be replaced. We need to remember that sweat is not just water; sodium should be included to avoid hyponatremia, and glucose is needed to meet higher energy demands and avoid hypoglycaemia.
When we exercise, our body temperature naturally increases to around 38°C. However, this can be further exacerbated if atmospheric temperature is high. When body temperature exceeds 39°C, it can cause serious health issues such as heat exhaustion, and in more severe cases, heat stroke, which requires immediate medical attention. Other risks associated with heat include the appearance of blisters, which, if left untreated, can develop into serious open wounds that need to be treated.
Acclimatization Protocols
What can you do to help with heat adaptation and make the experience slightly easier? First of all, adjust your pace to make it feel easier. Don’t worry; you are not getting slower! Hydration is key, and you can increase electrolyte intake to counterbalance the loss in sweat. If you have a competition in a warmer place, I recommend doing a heat acclimatisation protocol during tapering by incorporating 20-30 minutes sauna sessions. Since this is quite energy-consuming, it is not recommended to include it during peak performance to avoid interfering with training. Allow at least 10-14 days for this, and compete soon after, as the benefits from heat adaptation are very acute and don’t last long.
Takeaway Message
Even though training in the heat seems harder and makes us go slower, it stimulates changes in our physiology that boost performance. However, with its benefits, there are also some associated risks that can be easily prevented. Take it easy, enjoy, and listen to your body. Do some heat acclimatisation before competing to break records.
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