Heat acclimatization

You can bike in hot weather if you take it slow and easy.

Weather: Sunny and hot

I’m a wimp now that I live in California, but I got my start with ‘serious’ bike riding in baking hot Wichita Falls, Texas (home of the “Hotter ‘n’ Hell Hundred”). For three years I bike commuted 25 miles between Fort Worth and Irving, Texas. One memorable summer we had 90 straight days of temperatures over 90, with the mercury broaching 100 several times. The morning commutes were cooler, but riding on hot pavement every evening meant I arrived home with literal chunks of salt caking my skin, bike shorts and jersey. I’d lose close to 10 pounds of water every night, then lap filthy water from a hoof print and be glad to have it. I’d rehydrate over the next 24 hours and then do it again.

I lived in Texas, so I was used to the heat and I pushed myself without any problems. Healthy humans can and do become acclimated to higher temperatures with exposure to those temperatures. Heat acclimation or acclimatization is the natural process of your body adapting to change in the environment. While complete acclimatization takes up to two weeks, the results include improved tolerance for exercising in the heat with improved work output and reduced cardiovascular, thermal, and metabolic strain.

As your body acclimates to the heat, adaptations include:

  • Increased blood plasma volume from increased salt retention, which in turn results in…
  • Decreased heart rate, which results in…
  • Decreased perceived exertion, which allows you to work harder with less cardiovascular strain.
  • Autonomic nervous system ‘reprogramming’ redirects blood to the skin for better heat dissipation.
  • Earlier onset of sweat production.
  • More profuse sweating.
  • Salt conservation, through decreased excretion of NaCl in sweat and urine.

If you kept the miles on during the winter and spring months, you’re ahead of the game. Research shows acclimation occurs more quickly for people who are already fit. Acclimating to the heat occurs much more quickly for those who exercise.

Acclimation occurs more quickly through intense physical activity in the heat, but you need to watch yourself to make sure you don’t suffer heat illness. Sports physicians recommend weighing yourself before and after your workout to determine water loss. If you lose 2% to 3% of your body weight during the workout, drink more water. If you lose between 4% to 6% of your body weight in water, you need to slow down and reduce the intensity of your workout. 7% and above, and you should call the doctor.

Excess water and salts do not improve the acclimation process, but all of us realize that dehydration does impact our ability to keep cool. It is possible to overdo the water, and many endurance sport athletes overindulge in liquids, resulting in hyponatremia. Weirdly, some of the symptoms of hyponatremia — nausea, muscle cramps, mental confusion — mimic those of dehydration. Know your body by weighing yourself. The usual guidance is 8 oz of water for every 15 minutes of endurance activity, then weigh yourself afterwards. Conversely, Jobst Brandt — who cycled several thousand miles per year well into his 70s — famously never carried water on his bike.

Heat illness

If you’re not acclimated to the heat, you can go out and exercise, but watch yourself. Heat cramps occur after strenuous exercise accompanied with high water intake with few electrolytes. Heat acclimation decreases the risk of heat cramps.

Fainting can occur when when heat and humidity rise quickly. So much blood is shunted to the skin to reduce your core temperature that your blood pressure drops enough for you to faint or feel woozy. The risk of fainting drops to near zero after acclimation.

Heat exhaustion symptoms include headache, rapid breathing, fast weak pulse, dizziness and nausea. With those symptoms, you need to stop what you’re doing, find a cool spot in the shade, get wet and hydrate.

The next step beyond that, heat stroke, requires immediate cooling and medical attention. Symptoms include dry, hot skin, tachycardia, and significant mental impairment. You’re one sick puppy and you know it.

Get out and ride

You should respect the heat, but you don’t need to fear it. If you’re not acclimated, pay attention to your body and take it easy.

One Comment

  1. I am a HUGE pansy when it come to riding or running in the heat. I hate it, and my body hates it. I do however understand the significance of acclimating to the heat, at least within reason. I am unable to run (remember, I am first a runner, then a cyclist 🙂 ) on Saturday mornings like I’d prefer. But instead of “calling it a day,” I realize I can ride a bike in the warmer temps and find some hills to work my quads (which in turn benefit me as a runner).

    Races often end in much warmer temps than when they start. Why wouldn’t I take small action steps to help me finish strong? Good information in this article. 

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