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The Art and Science of Fitness | The do’s and don’ts of exercising on a hot day

Exercising and playing in hot and humid conditions, for as little as 30 minutes, can quickly take a turn for the worse. Exertional heatstroke happens to be one of the top reasons for sudden death in sport, but unlike other conditions, it’s both easily preventable and treatable even by non-medics — if they are aware of some fundamentals. Unfortunately, most event organisers and coaches don’t have a clue about this. No, gulping down gallons of plain water isn’t the solution. It makes the situation worse.

A decade ago, on a hot summer Sunday on my long slow run, I started to sweat from the first kilometre and my t-shirt and shorts were soaking wet by the second. Nothing extraordinary here, as most of you will probably relate to this in current weather conditions. After about three hours, I hit Rajpath (the road between Rashtrapati Bhavan and India Gate) and the sun was shining in all its glory, as if there was no tomorrow. The temperature had snuck up to about 30°C, which didn’t seem like a big deal, but with 80% relative humidity, it felt like 40°C. I wasn’t tired and there were no aches or pains, or at least that’s what I thought. Suddenly, out of the blue, I had the urge to sleep. It baffled me.

Rather than continue running, I headed towards one of the trees lined up the lawns on both sides of Rajpath. I lay down on a bench under the tree. It seemed as if someone had switched on the air conditioner, as temperatures seemed to have dipped by 10°C.

Now, this could have easily been disastrous, had I not stopped. More so for those who are not accustomed to exerting themselves by playing sports or exercising in these conditions. And if your fitness levels aren’t good, these are just the wrong weather conditions to have an epiphany to discover your fitter self. When it’s extremely hot, it’s best to stay indoors and focus on strength and conditioning, so that you are better prepared when you do decide to exercise outdoors.

It’s interesting to note that the mechanical efficiency of us humans is ≤30%. As soon as we start exercising or playing sport, our contracting muscles waste a lot of energy by producing large amounts of heat. We release that heat through sweat. When the ambient air temperature is lower than the body, the sweat evaporates and cools the body down. And it’s all good.

But when air temperature and humidity make the temperature feel higher than that of our bodies — ie more than 37°C — the sweat doesn’t evaporate, but drips. Sweating effectively fails to keep us cool, and as a result, it heats us up further. Soon, your t-shirt will be soaking wet — much like the way it was for me on that fateful day. Also, if we are pushing too hard, it makes the situation even worse. Some of us — who are adamant to carry on exerting ourselves because of being excessively motivated, due to peer pressure, or because of a rookie coach pushing us too much — start experiencing confusion and excessive aggressiveness that doesn’t match our character.

To cool down, our body again tries to sweat even more, leading to an increase in skin blood flow, compromising on the blood flowing to the vital organs such as the heart and brain, putting us at risk of multi-organ failure. This overheats our body if we don’t quickly stop, reduce the intensity of exercise, and rapidly bring the core body temperature down, along with pouring copious amounts of cold water on our face, head and all over the body, consuming cold fluids and immersing the whole body in ice cold water. The simple act of pouring cold water on your face and drinking ice cold water quickly sends blood flowing back to your core and maintains the crucial oxygen supply to your gut, heart and brain, reducing the body’s core temperature.

The very basic thing is that we need to match our levels of physical exertion in hot and humid conditions to no more than our current physical fitness. What helped me that day was that I had been running for the last 27 years (now, 37) and I am used to running in hot conditions. Usually one of the earliest signs of heat illness is confusion and lack of appropriate decision-making. Luckily, I was still in my senses to put my ego aside to decide mid-run to stop and lie down under a tree.

Even if we are fit, during summers, it is important to avoid peak hot times and wind up our runs latest by 7-7:30 am when temperatures are still reasonable and the sun is not going nuts. In any case, we need to acclimatise to exercising in the heat if we are going to be participating in an event while we are unaccustomed to hot and humid conditions.

A classic example is the Mumbai Marathon which is held in January. Runners from northern parts of India go from cold and dry weather conditions to moderately hot and humid Mumbai conditions, and then wonder why they didn’t do as well as their training suggested, and at times mess up completely, if not land up in the hospital. They need to acclimate to exercising in heat by doing 60-90 minutes daily for 1-2 weeks before the event. This will also help their performance.

The simple act of drinking ice cold electrolytes and ice slurry, wearing ice vests, and spraying water on the face, head and neck before the exercise or sport help bring down the core body temperature. And when the same is done during and after the run too, quickly sends blood flowing back to your core and maintains the crucial oxygen supply to your gut, heart and brain, reducing the body’s core temperature. And it’s important to take off your shoes and socks right after too, as the soles of our feet have the highest density of sweat glands.

Wearing light-coloured loose, breathable clothes helps in letting the sweat easily evaporate, thereby keeping us cool. Remember that plain water alone isn’t the solution, so do start getting used to consuming electrolytes even at rest, so that your body can tolerate it a lot better when exercising, else rather than running to the finish line, we just might end up running to the loo. During our sporting activities, we need to plan our hydration well. The one big tip is to take fluids in sips every 15-20 minutes, rather than gulping them down. It’s also a great idea to have about 300-500 ml of cold water and electrolytes spread over the three hours before the strenuous activity in the heat. That helps in reducing the core body temperature.

During marathons, most runners who collapse and then require ambulance assistance are caused by exertional heat illness. Rather than thinking of this as someone else’s responsibility, if a situation like this were to happen, I think that it is not only our right, but our duty to make ourselves more aware, and practice the same too. You could end up saving your own life or the life of someone around you. Remember, it’s all good, until it’s not.

Keep miling and smiling.

Dr Rajat Chauhan is the author of MoveMint Medicine: Your Journey to Peak Health and La Ultra: cOuch to 5, 11 & 22 kms in 100 days

He writes a weekly column, exclusively for HT Premium readers, that breaks down the science of movement and exercise.

The views expressed are personal

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