Posted on: Oct 27th, 2019 by adminva | Categories: Physiotherapy

Important Considerations with Exercise in Hot Conditions

After Reece’s massive run in the 102km Tarawera Ultra Trail Race on Saturday and the triathlon racing season getting into full swing it’s the perfect time to share some wisdom about exercising in hot conditions.
There is no doubt that the recent weather conditions are making life uncomfortable. The record temperatures are more extreme and more prolonged then any of us have experienced before. The goal of this blog is to discuss the important things to consider when participating in sport, work or any strenuous physical activity in the heat.
Much of the research into exercise in hot conditions comes from the big marathons. Famous incidents such as in the 1984 women’s Olympic marathon in LA with Gabriela Andersen,

Gabriela Andersen 1984 Olympic marathon finish

and more recently the collapsing of Callum Hawkins of Scotland at the Gold Coast Commonwealth Games

Callum Hawkins collapse at 2018 Gold Coast Commonwealth Games

grabbing media headlines and spark debates about the safety of racing in the heat and how we can prepare.

How the body adapts to hot conditions:

The body will always prioritise survival over athletic performance. Therefore blood is moved from the working muscles to the skin to produce sweat. Sweat when evaporated off the skin helps cool the body. The increase in sweat rate also changes the volume of fluid in blood. The blood becomes much thicker as there is less fluid (plasma), but still the same amount of cells and enzymes. These changes mean that less blood is being sent back to the heart and therefore the left ventricle will pump less blood back into circulation. Because the heart is no longer pumping as much blood during each stroke, it must beat faster to compensate.
When the blood plasma levels drop too low the body will stop sweating to retain a certain level of fluid in the blood, which prevents the blood from thickening to a severe level causing a stroke or heart attack. Now with the lack of sweating the core body temperature will begin to rise rapidly. When the core body temperature rises up to ~41°C the brain will stop sending signals to the body causing a loss in coordination. The body will then collapse to prevent the muscles from working and stop the core temperature hitting a critical temperature resulting in death. Both Gabriela and Callum fell victim to this process.
Not only does the above process prevent catastrophes from occurring, it can limit endurance performance. It is important for endurance athletes to adapt their daily training efforts to the environment. Hot conditions reduce an athlete’s time to exhaustion at a constant workload. Every individual’s adaption period to heat is different, as muscle mass, exercise intensity, and genetic sweat rates all contribute.
Our best advice; make your training plan specific to your body and the environment.

The Dangers:

Heat related illness occurs when either the body is unable to lower the core body temperature as normal, or heat production is excessive due to the combination of physical activity demands and environmental conditions.
Performance in the heat is affected by the interaction of exercise duration, intensity, hydration status and the environmental conditions, particularly temperature and humidity as they influence the body ‘s ability to loose heat.

Dehydration contributes to a decrease in performance differently depending on the air temperature. The loss of 4% body weight from dehydration declines performance at different temperatures as follows:

• 40°C = 23% ⬇️
• 30°C = 12% ⬇️
• 20°C = 5% ⬇️
• 10°C = 3% ⬇️
Now you know what’s happening in the body. But how will you feel? You’ll feel unwell! Sometimes seriously, with reduced brain function leading to reduced coordination, judgement and ability to continue. In the worst cases death is possible as outlined earlier.
The most dangerous situation we get presented with at marathons and at ultra distance events is hyponatremia. This is where you sweat, losing fluids and electrolytes, particularly sodium and potassium, then drink large volumes of water, reducing the concentration of the remaining electrolytes, affecting your heart function. Then we have a problem!

How To Prevent Heat Injury and Optimise Performance

The advice on this has changed more than anything else. Initially we were told to drink when thirsty, then it was decided that by that time you would already be dehydrated. So the advice changed to drink often regardless of thirst, which we now know isn’t the safest practice so now we advise drinking a little when you’re thirsty. The minimal weight loss from drinking to thirst and not to a plan has been shown not to lead to a significant reduction in performance. By drinking to thirst we are reducing the risk of hyponatreamia, which is actually more dangerous than severe dehydration. Our advice, trial your hydration before your event as every individual needs their own specific hydration method. This can be as specific as trialing a particular flavour of drink and different flavours can effect the stomach differently and race day is not the time to experiment.
Be hydrated before you start by Increasing your fluid intake over the days before an event. This will help to avoid consuming large volumes on the day and during the event that can leave you feeling bloated.

Water Immersion
Water Immersion is a useful cooling method both pre-event and post event. Pre-event immersion for 25-30mins in temperate water of 25°C-28°C has been shown to reduce core body temperature. Don’t be fooled into colder is better. Research has identified water immersion for 5mins in a temperature <14°C, resulted in too much vasoconstriction of blood vessels (shivering), which is the body’s mechanism to retain heat. Stick to the cold water immersion post event.
Crushed Ice Ingestion
Consuming crushed ice slurry drinks can decrease core body temperature and improve time to exhaustion during submaximal exercise intensity. This is very useful technique to employ both before and during submaximal levels of exercise.

Dress Appropriately
The fancy dress is fun and makes for a great spectacle but they are not typically constructed of appropriate materials and those runners are likely to have a bad day! For the rest of us though, there are plenty of options and really amazing materials to help manage heat.
Slow Down to Cool Down
The harder you work the more heat you generate so if you’re getting too hot, slow down, cool, then get into it again. In field sports you have the opportunity to hydrate regularly, drop back, rest during breaks in play or sub off and ideally the bench will be aware of fatigue, altered skills and coordination and rest players as required.
During the 2016 World Cycling Championships in Doha, many cyclist swallowed thermometer pills before the different events to measure peak core temperatures. The results showed higher core body temperatures during the 45min time trial compared to the 6-hour road race. Therefore the main factor in how hot you get is how intensely you’re exercising.

Avoid Alcohol
Sorry, but be sensible and save it for the celebrations. Ensure you’re hydrated with an easy field test; make sure you’re peeing clear leading up to race day.

The Benefits of Heat Training for Performance

Not all aspects of exercising in the heat are bad. Heat training and acclimatisation can actually produce many physiological adaptations which can improve performance in both hot and cold conditions.

Heat training adaptations improve the body’s ability to open up the vascular pathways and allow increased blood flow to the skin. Increased blood flow to the skin produces a higher sweat rate and the ability to cool the core body temperature. As individuals adapt to the heat this process becomes more efficient and the ability to control core body temperature is improved.

•Increases in sweat rate
•Blood flow to the skin increases and
•Plasma volume expansion

If you have any specific questions related training in the heat, managing recovery or heat injury or if you are involved with teams or events and would like to discuss minimising the risk of heat related injury get in touch.

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