In the first post about training in the heat (Heat Sickness Starts At Night), I emphasized how your habits around food and water have a huge impact on your heat exhaustion risk.

Nothing has changed about that; you have to fuel the work in advance of starting the work to be best armed against hot conditions.

But two incidents this week remind me how critical it is to be adaptable to stay safe on hot days.

Nature Laughs At Your Plans

The first incident was my wife’s run test.

She’s an experienced triathlete who got started in Texas summers over a decade ago. She’s a vocal proponent of #eatmorecarbs. She is diligent about fueling her work, about getting plenty of water and salt  before training, during training, and after training. She wears her sunscreen and her sun shirts and her hats with discipline.

But when her training plan had a 10k time trial run scheduled on a work day, she had to make a tough choice: run at dawn on no real food or run at midday having had breakfast.

She chose the latter, hoping more fuel on board would be worth the temperature trade-off. I paced her (from a bike, let’s not be ridiculous; I don’t run more than 60 seconds!). I also carried her water and planned to replace it halfway through, as she was testing her 10k over multiple loops around our neighborhood.

Well, despite a good breakfast timed appropriately, carefully dosed and timed pre-test nutrition, and all her standard sun precautions, she had to bail at 5 km. By that point, her pace had fallen off nearly 90 seconds per mile, she was walking and running in equal parts, and she was sweating less and less. Her heart rate had started to fall when she announced she *might* quit. By the time she *did* quit, her face was beet-red yet her shoulders were pale.

I handed off cold water and gave her time to walk back to the house. I got a cooldown station ready in the living room – a yoga mat, a fan, and cool, dry towels – and grabbed her saltwater bottle. It took over an hour for her heart rate to settle near normal, then several hours more for her skin color to normalize.

That, folks, is heat sickness. My wife knows it well and handled it well, all things considered. But it’s a huge risk to try to push through. Conditions that day: 90deg F, UV index of 7.5, stagnant wind, at 20% humidity. Not unbelievably hot, but plenty hot enough to do damage.

The Best Metaphor For Hot Days Ever

The other incident was a long-time remote athlete’s sleeplessness. We got off easy on this one – no harm was done and no real risk was taken. It happened to be that she woke up much earlier than usual one day and felt good enough to train. So she took a speed session before dawn, which is an awesome way to escape the heat.

But THEN she had a session of stairs and jumps that typically occurs at a shadeless heat sink of a public track. Great place to train but rough in the summer. So she moved that session to a parking garage “because the sun is a DEATH LASER” (emphasis mine).

I love that metaphor. The physics nerd in me appreciates that it’s not even inaccurate, really, since light is EM waves and the risks of UV exposure include lethal cancers and immunosuppression. You have to take sun exposure seriously to have a long career in sport.

What You Can Control On Hot Training Days

When you need to train in summer, remember that the sun is a death laser.

• Limit your absolute exposure, then limit its duration.
• Cover and protect your skin.
• Drink water all day, every day, and extra around training.
• Fuel your work.

Even still, no matter how well-prepared you are, sometimes the heat and exposure are just too much.

Don’t ever push through. There’s no prize for being stupid…or, ahem, “tough.” Better to cut a session short today, rehydrate, and be ready to crush the day tomorrow than to experience deep heat exhaustion or heat stroke then end up in a hospital.

Letting your body overheat does a lot more damage than a single night of sleep can fix. No single training session is worth those risks to your health. Heat acclimatization takes time. It takes several days of short exposures and gradually increasing exercise intensity. You can’t shortcut that process and you gain little by trying to.

Hikers know that the mountain is indifferent to your existence, so you have to both be prepared for changing conditions and be willing to quit based on what nature offers you.

As a death laser, the sun is overtly hostile to your existence. You have to respect it as such. Adapt to what nature offers you. If, on a particularly hot day, that offer doesn’t include training safely, don’t sweat it.

A Little Bonus For The Geeks

By the way, here’s Quanta on the sun’s options for destroying Earth some years from now. This is weekly reading for me, so if you’re nerdy enough to read or listen to the whole piece, send me an email to talk about it!