Heatstroke and Injury Prevention

What is Heatstroke?

Heatstroke, or exertional heat illness, is a group of conditions that result from doing strenuous exercise or excessive activity in the presence of heat, humidity, or other factors that make it difficult for the body to maintain a constant balanced temperature. Heatstroke can be a medical emergency, but often the lesser transient type of heat illnesses are the ones we are all familiar with (Giersch, Belval & Lopez, 2020).

What Causes Heatstroke?

Our bodies are very good at achieving and maintaining a state of balance in all of the systems required for survival, a state of being called ‘homeostasis’. Imbalance occurs when we can’t regulate our body temperature due to exposure to excessive external heat or a lack of ability to cool down, e.g. dehydrated from excessive sweating.

Medically speaking, heatstroke is occurring when the core body temperature is higher than 40℃. However, the patient doesn’t need to have a temperature at or above 40℃ for life-threatening situations. So while a high temperature is dangerous, a lack of a high temperature shouldn’t be a sign that nothing serious is going on (Giersch, Belval & Lopez, 2020).

Dehydration

Dehydration is a condition where there is a lack of fluids in the body or a lack of specific dissolved salts or electrolytes in that fluid, leading to poor body and mind function. Dehydration can occur in various ways, including illness, forgetting to drink enough water, and excessive sweating. Our bodies cool by sweating, but if we’re dehydrated, we can run out of water to sweat out, and our core body temperature rises (Vic State Govt, 2015).

Heatstroke and dehydration can occur together, although this is not always the case. Both are common in our active and sporty Australian society; both in our organised sports for both children and adults, recreational sports like surfing and hiking, and outdoor lifestyle, like beach days and backyard cricket.

Lack of Airflow, Crowded Conditions

If you’ve ever been to a summer music festival, hiking in waterproof clothing, inside a busy nightclub or stuck inside a full elevator, you’ve experienced this one. Escaping the radiating body heat from yourself or others when you’re insulated can be tricky, even impossible. When you’re close together for long periods, your body can’t escape this radiating heat, and your internal temperature stays high (Giersch, Belval & Lopez, 2020).

Sun Exposure

Everyone loves a nap after a morning spent at the beach, but this exhaustion is a form of heat illness often accompanied by dehydration. Not to mention the thirst, fatigue and pain if you wake up from that nap with a sunburn.

Australia routinely runs sun exposure and sunburn awareness campaigns, and workplaces often supply mitigation – hats, sunscreen, water, and shade resting areas. About a quarter of the Australian workforce, who work in the sun, particularly people who work in the middle of the day, are at increased risk for sun and heat exposure (SafeWork Australia, 2020).

Bushfires

Even if you’ve never had the bad luck to experience a full-blown bushfire, you’ve probably stood a little too close to the campfire. A slightly lesser version, but you might have had an oven, stove and slow cooker going in a sunny kitchen – the heat feels inescapable. Radiant heat can quickly cause dehydration, heat illness and exhaustion. Bushfires typically occur when the air is scorching and dry, compounding the dehydration and heat illness risk factors (Vic State Govt, 2015).

Heatstroke Symptoms

Usually, heatstroke and dehydration can be diagnosed clinically, with a check for these signs and symptoms. Scans or blood tests typically aren’t needed.

The simplest way to tell if you’re experiencing dehydration is to have a look at the colour of your urine. You might have seen charts like this pop up on the back of toilet doors in the last few years, especially in public toilets.

(Healthdirect, 2019)

Why is this Important for Physiotherapy and Sports Performance?

As physiotherapists, it is our job to keep our athletes safe when looking after them from the sidelines. Player wellbeing includes understanding the complex interactions between ‘medical’ health factors and ‘physical’ health factors, as well as emotional, psychological and societal factors. Heat illness is becoming increasingly important to understand as average temperatures rise (Kakamu et al., 2017).

There is a lack of research around whether extremes of temperature lead directly to injury during sport. The lack of research is possible because it is unethical to subject people to hard work at various temperatures to see who gets the most injured. After all, we already have researched how detrimental it can be to our brains and bodies. There is evidence mostly in occupational, military and industrial settings, as well as lab research that guides us in decision making for keeping our patients (both athletes and workers) safe in sweltering conditions. Several factors loosely point towards increased heat exposure leading to an increase in injuries.

Cognitive Functions

A study completed by researchers in Iran (Mazloumi et al., 2014) found that working in heated conditions led to a slow down in reaction time and a more inferior selective attention ability (the ability to focus on one thing without getting distracted).

The Journal of American College of Nutrition (Lieberman, 2007) published an article called ‘Hydration and Cognition: A Review’. The article discussed a variety of different studies grouped by the way they induced dehydration. The research they found was most robust in the ‘heat or exercise’ method of dehydration, showing a consistent downward trend of cognitive abilities with dehydration measured at 1%, 2%, 3% and 4% of body weight when subjects tested for hand-eye coordination, symbol substitution and a concentration test.

Again, don’t forget your day at the beach – that nap that you need..? Well, it’s shown that the cognitive deficits (like poor coordination, reduced information processing, decreased memory and attention span) may show up after 1-2 hours after exposure, from as little as a 1.8℃ increase in core body temperature (Walter et al., 2016). You need a nap because your brain is slowing down to recover!

Productivity

In a large multi-country study, 30% of workers worldwide experienced a reduction in productivity while working in hot conditions (Flouris et al., 2018). Also, the same study found that proper medical assessment and risk prevention measures for mitigating heat stress in employees significantly reduced lost-injury time and returned workers to their jobs safely in mining, military, and firefighting industries, as well HAZMAT workers.

Muscle Cramping

Muscle cramps are painful sustained muscle contractions or spasms. We know that these cramps are due to changes in the nervous system, but there is some weak evidence to suggest that heat and dehydration can contribute to an increased incidence of cramping (Miller, 2018).

Muscle Function and Strength

In a 2019 study (Racinais et al.), researchers took volunteers and asked them to perform sustained maximal muscle contractions. They found that when volunteers were heated up first, they subjectively reported their strength felt the same, but in fact, their muscle contraction wasn’t as durable over time. The peak torque and peak voluntary activation of fibres both dipped after only 20% of the contraction length. However, it found that heat acclimatisation can partially compensate for these effects. This finding is in line with other research suggesting that training in the heat can maximise competitive performance in hot weather.

Balance

Proprioception is also known as joint position sense and is used to balance and orient us in the world around us.

A joint Qatari-French study from 2018 (Mtibaa et al.) showed that inducing a state of hyperthermia (increased internal body temperature) produced worse results on several balance tests. This finding is suggesting decreased ankle proprioception. Participants asked to balance on one foot in various tasks found that the participants were balancing after they were passively heated up needed more contact with the ground to compensate for lack of joint sensation. Plus, quicker active electrical signalling to the muscles from the brain after the heat suppressed the regular stretch H-reflex from the spinal cord.

The same group of researchers took another look the following year (Mtibaa, 2019) to look at ankle proprioception in a treadmill test. Participants were asked to run at their own pace, either with or without environmental heating, ran in the heat ran slower, and with more movement error at the ankle. But this was well compensated for further up the body. This change in movement was consistent with other previous studies showing this change with runners experiencing exercise-induced fatigue.

Intestinal Permeability

It’s a funny term, but intestinal permeability refers to the ease with which certain substances and bacteria pass through the intestinal wall into the bloodstream. Usually, these gaps between cells are tiny, so the cells themselves act as a gatekeeper and filter. They decide which good things can come into the bloodstream, travel to the rest of the body, and keep the bad stuff like intestinal bacteria, indigestible food, and bile in the intestine to be passed out as waste.

Hyperthermia leads to a state of high intestinal permeability; that is, the gaps between cells get more prominent, allowing some substances to ‘slip through the net’ and pass into the bloodstream. If these things are nasty, the immune system creates a systemic inflammatory response to target and neutralise the potential danger. Systemic inflammation, significantly when prolonged, has contributed to disease risk and reduced sporting performance (Pires et al., 2017).

What are the Heatstroke Treatment Options?

Treatment for heat illness and dehydration is relatively simple – cooling and rehydration. It’s essential to treat slowly to allow the body time to readjust, or it’s possible to make things worse. If you’re not sure, a call to 1800 022 222 or 000 is appropriate for guidance.

Your pitch-side physiotherapist is trained in advanced first-aid, including heat-related illnesses, in addition to their injury treatment training and experience. In the case of suspected acute heat-related illness, you can ask the physiotherapist or other health professional present at the game to assess you and guide you on the next steps for treatment and advice, if appropriate. Suppose you’re looking to improve your balance, muscle function, efficiency of movement and strength to counteract the effects of heat while playing your sport. In that case, you can book in to see one of our physios who will thoroughly assess you and recommend a treatment plan.

If you have any further questions, please ask your physiotherapist.