Heat injury during exercise:
How to tell the difference between Heat Stroke, Heat Exhaustion and Hyponatraemia and what to do about them
With Summer weather on its way there also comes with it the risk of suffering heat injury during strenuous exercise; be that during a hike in the hills or during an organised event like the Oxfam 100km Charity Walk.
There are three types of heat injury (Heat stroke, heat exhaustion and hyponatraemia) that one must be aware of and it is essential to know the difference between the three because the emergency action and medical treatments are different and if you, or the medics get it wrong, things can go from bad to much worse!
This is most common during short, sharp exertion in warm or hot conditions, such as may be experienced during a five kilometer fun run, or when struggling up a very steep slope under a heavy back pack. If dehydration is present, it is mild. Heat stroke is most commonly suffered at the beginning of Summer in the less conditioned participants and in those who have had little recent acclimatisation to warm conditions. High humidity may be an additional factor because humidity reduces the effectiveness of evaporative cooling from sweating.
Symptoms of heat stroke:
- Extremely high core temperature of up to 41°C.
- Hot, red, dry skin (Little or no sweating).
- Someone with heat stroke has stopped sweating, due to a failure in his or her heat control system.
- Rapid pulse.
- Rapid, shallow breathing.
- Headache (may be extreme).
- Speeding up to “suicidal” pace, if in a race.
- Confusion, aggression, strange behaviour such as trying to keep running even while lying on their backs.
- Possible loss of consciousness, or falling in and out of consciousness. If unconscious, failure to recover consciousness when laid down and with legs propped up.
Consequences of heat stroke
High core temperatures damage the internal organs, especially the brain. Any fluid loss can also produce dangerously low blood pressure. Most people who are killed by heat stroke die when their heart stops pumping effectively (circulatory failure). Even people who survive are likely to have permanent brain damage if their core temperature has been over 40.6°C for more than an hour or two. High temperatures damage delicate cell materials and structures, such as proteins (think of cooking egg white). High core temperatures speed enzyme activity in the cells, causing an internal equivalent to a nuclear melt down – more and more heat is produced even after exercise has ceased. Effective emergency action to reduce core temperatures is critically important.
Emergency action for heat stroke
- Stop the victim from
exercising. A person suffering heat stroke may aggressively resist
assistance, even if lying semi-conscious on the ground and may
continue to try to run/walk or even crawl through the gorse
undergrowth (I have had to deal with this during an incident at a
mountain bike race).
- Place in the “Recovery
- Call emergency services
– Heat stroke is life-threatening – They need expert medical
care without delay.
- Get the victim out of the sun;
but keep in a breeze if possible.
- Cool by pouring water over the
torso and limbs and fan vigorously for convective cooling. If
available, immerse their torso in an ice bath.
- Only give small amounts of
liquid at a time and only if conscious in case of vomiting.
- Once initially stabilised,
they must be transported the quickest way possible to hospital –
Like by helicopter.
The symptoms of heat stroke differs from those of heat exhaustion. Heat exhaustion is
experienced towards the end of long, moderately intense exercise,
when the combination of exhaustion, dehydration and heat may bring
|Lorraine: Very dehydrated; but prepared!|
Symptoms of heat exhaustion:
- Moderately high core
temperature (the temperature of the body's internal organs, best
measured with a rectal thermometer) of up to 39°C.
- Cool, pale, clammy skin.
- A person suffering from heat
exhaustion will usually be sweating profusely in an attempt to get
rid of excess heat.
- Muscle cramps.
- Fatigue and weakness
- Drastic drop off of pace, if
in a race.
- Dizziness or light headed.
- Possible fainting, but can be
revived by laying down and propping up the legs.
Consequences of heat Exhaustion
The consequences of heat exhaustion are usually much less severe than heat stroke or hyponatraemia and it generally does not constitute a medical emergency.
The reason heat exhaustion is not a dire medical emergency is the loss of fluid and depletion of energy (hypoglycaemia) prevents the body's metabolism from from going into “hyper-drive” or “melt-down”. The victim merely shuts down to the point where they can no longer proceed.
There is a potential for kidney damage. The most frequently suffered consequence is very sore leg muscles for several days – more so than what would be expected from delayed onset muscle soreness, post exercise.
The most immediate consequence of heat exhaustion is the person will grind to an exhausted halt as the event proceeds and may even faint. Fainting can be very disconcerting to those about them because it may appear they are suffering a heart attack, stroke or epilepsy.
Slipping into a chilled state (hypothermia) within minutes of ceasing exercise is a real risk and often the case. This is because the exhausted person is unable to generate enough body heat that is sufficient to maintain core temperature.
Recovery is usually very quick, once the person has rehydrated and well on the way to topping up their depleted energy stores.
For an example of how distressing heat exhaustion can appear to be, please refer to this Youtube video of Gabriela Andersen-Scheiss staggering into the Olympic Stadium, Los Angeles, 1984. She was suffering from heat exhaustion and was determined to finish no matter what. While she looked awful and stirred up a huge controversy about whether or not she should have been pulled from the race, she was out dancing with several of the other runners later that evening, including my sister, Lorraine (Lorraine, came 5th in that race):
Here is another Youtube example of heat exhaustion combined with hypoglycaemia:
Emergency action for heat exhaustion
- Stop the person exercising and
have them lie down, in the shade, with legs propped up so that blood
flows to the brain.
- Cool the person by fanning
(usually not necessary to chill with water).
- Rehydrate with a mix of sugary
drinks (fruit juice, sweetened tea) and electrolytes (a simple and
effective electrolyte solution is water with a ¼ teaspoon of pink
salt per liter.
- Keep warm: It may be necessary
to cool the person initially, but be aware that a person suffering
heat exhaustion may quickly slip into a chilled sate, so have
blankets, sleeping bag, jackets, a hat and other warm clothing at
- Avoid hot spas and baths until
fully hydrated and re-energised otherwise the person is liable to
pass out due to already low blood pressure plummeting even further.
- Do not stand around later on at the prize-giving, for example. If one must attend, then be seated or even sit or lie on the floor and take care when standing up quickly because the blood pressure may be very low and fainting is a possibility.
Hyponatraemia is now the leading killer during organised events such as marathons, ultra-marathons, adventure racing and Iron Man triathlons. In my opinion, hyponatraemia is the consequence of excessive influence of numerous water and sports drinks companies in popular sports media and with event sponsorship. These companies have deep pockets and they want participants to drink more product – not less with the result that the need for “hydration” during exercise has been promoted to the point of hysteria.
The voices of reason have been “drowned” in the promotional deluge.
Once virtually an unknown condition, it is now commonplace. Researchers found, for instance, that 13% of the athletes who finished the 2002 Boston Marathon were in a clinically hyponatraemic condition. Tim Noakes' 2012 book "Waterlogged" addresses this phenomenon.
Hyponatraemia occurs as a result of a proportional excess of water relative to the plasma sodium (salt level in the blood). I call it “Soggy Body Syndrome” in which the body becomes full of water. Unfortunately, this swelling also occurs in the brain. With no room to expand in the skull, the brain is progressively compressed ultimately resulting in brain death. Needless to say, all suspected cases of hyponatraemia must be treated as a medical emergency.
Symptoms of Hyponatraemia
warning signs are often subtle and may be similar to heat exhaustion
or heat stroke and include
- Nausea – vomiting.
- Muscle cramps.
- Slurred speech.
- Severe headache.
Hyponatraemia is rare among the front runners in events like the marathon. This due to them being unable to drink more than a few cup-fulls while running at pace and their finishing in short time. Those most at risk are the “back markers” and walkers who have plenty of time to drink large amounts of water and are exercising at a rate that allows them to hold it down, due to less sloshing about in the tummy!
Excessive fluid consumption before and during and longer finishing times are the primary risk factors for developing this condition.
Vomiting may be the only clinical sign differentiating hyponatraemia from other conditions that induce exercise-associated collapse. Weight gain (If pre-event weighing has been done) during the event is another clue of hyponatraemia possibly being present.
The natural response of a distressed athlete and those administering care, is drink even more water because they think the problem is to do with dehydration. Unfortunately, water alone will increase the problem of hyponatraemia. At the most extreme an athlete may experience seizures, coma, or death.
Hyponatraemia (and other heat-related conditions)
The best way for an athlete to avoid such problems is to train in similar environmental conditions to what is anticipated on the day and to drink only what is required to replace what fluid is lost – Not more.
My most glorious sporting achievement was getting second place in a 20 mile race around
Rarotonga in 1988: The good old days of “Big Hair”, beards and no official water stations!
|Very, very humid, no water stops and still 15 miles to go!|
The race featured World mile record holder, John Walker, and reigning New Zealand Marathon Champion, Graham Struthers (That's me in the “Putaruru” singlet). I came second, not so much due to ability and more to do with having spent several weeks cunningly heat acclimatising during a long, cold New Zealand winter in preparation for the tropical heat and humidity of the Cook Islands.
How to avoid Hyponatraemia:
Much of what follows applies nicely to preventing heat stroke and heat exhaustion as well:
- Acclimatise by training for
several weeks in conditions that simulate the anticipated conditions
of heat and humidity. This includes training during the heat of the
day, wearing extra clothing and conditioning your body to tolerate
some dehydration by drinking less than you think you need while
exercising (Make up for the losses after
the exercise). Please read my article here for more about how to
use a sauna to acclimatise for exercise in heat:
- Get really good at listening
to your body: Drink according to the first subtle sensations of
thirst, rather than by a fixed hydration rule. A good way to gauge
how accurate you are at listening to your body signals is to weigh
yourself immediately before and after exercise. Take account of
what is drunk during the exercise. A kilo lost or gained is
equivalent to one liter of water gained or lost. Adjust drinking
during the next exercise session accordingly. Do this often during
training so that you get a good feel for it.
- If you are peeing with
“normal” regularity, then you are probably keeping well
hydrated. If you are constantly running off to the toilet,
including all hours of the night, and peeing large volumes, you are
probably drinking too much.
- If you have constant
headaches, there is the possibility that you are over-hydrating.
- Use a sodium containing sports
drinks during long distance, high intensity events (more than 60-90
minutes long). I think the best is a bottle of water that is lightly
salted with a pink multi-mineral salt, rather than refined salt
which provides just one of the dozens of different minerals that are
lost in sweat. Fruit juice can be added to provide carbohydrate
- Increase daily salt intake at
least several days prior to competition (except for those with
hypertension). Salt food generously with a pink multi-mineral salt,
rather than refined salt.
- Try not to drink more then you
sweat and pee out. Before, during and after weighing is a the best
way to tell.
- A good rule of thumb when
doing strenuous exercise for longer than an hour is to drink about 1
cup of fluid every 20 minutes.
Emergency action for hyponatraemia
- Stop the person exercising and
have them lie down, semi-reclining, in the shade..
- Shift into the Recovery
Position, if unconscious or if feeling nauseous (They may vomit
- Call emergency services:
If the person is suffering hyponatraemia, they require
urgent medical assistance, including intravenous electrolyte
solution to restore sodium balance. They have to get to
hospital the fastest way possible - Like by helicopter.
- If conscious, give a palatable
salty drink (If it is too salty, the person will feel even more
nauseous and may vomit). If they feel feel more nauseous after
drinking a salted liquid, give a cup or two of plain water to dilute
what is in the tummy.
- A simple and effective
electrolyte solution is water with a ¼ to level teaspoon of pink
salt per liter (Taste it to make sure it is palatable before administering it).
- Keep warm: It may be necessary
to cool the person initially, but be aware that a person suffering
hyponatraemia may quickly slip into a chilled state.
Heat injury during prolonged, intense exercise, be it a marathon, or a hike in the hills, is a hazard that is easily avoided; but easily suffered. Prevention consists of acclimatising for the anticipate conditions and a sensible approach to hydration – not too much and not too little. In the end, it comes down to listening to your body's subtle signals of distress, be it thirst, or getting too hot, for example, and then responding accordingly.
The only marathon I ever pulled out of was half way through the Otago Championships, held at the end of a long Southern Winter. A hot North-Westerly wind was blowing and competitors dropped like flies as the race proceeded. Come the halfway point, I was still upright, running freely and well-placed! Being familiar with the signs and symptoms of heat stroke, it soon dawned upon me that I was quickly running into trouble: I was nearly sprinting with still another 20 kilometers to go, I had stopped sweating profusely and I felt as if I was in a euphoric dream – Chariots of Fire – Here I come! I saw sense and stopped – Best decision in a long time, for sure!
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