Originally Posted by balesmachine

How to bicycle better in the heat.

Here is what I’ve learned from my 48+ years of riding in the heat. I live in Fort Worth, Texas. I’ve haven’t lived here my whole life . . . . yet!

Texas summers can be pretty hot, for sure. I’ve always done well in the heat, and I’ve been asked what’s my secret. I think the recipe for doing well in the heat is, ready for this, ride in the heat. Seriously though, I think my secret is riding 1 to 1.5 hours during the hottest part of the day. Do it two or three times a week. Don’t go longer than that during this “training” session. Pretty soon, your body will know exactly what to do when it’s hot. Most folks can endure this length of ride. It's short enough that dehydration shouldn’t be a factor. I’ve always commuted to work. I try to do it two or three days a week during the warm parts of the year. I am the worst cold weather wimp, I admit.

I recently had a good friend that bonked on a very hot weekend ride. I met him a few weeks later and he said he went to the doctor, and found out his pituitary gland wasn’t working right, and got a little pill to take and everything was better. This spurred my interest, and I started searching out just what your body does, when you exercise in the heat, especially riding a bike. Here is what I learned.

I admit that I may have some of the details slightly off, but the general facts stand true (I think).

Your hypothalamus resides in your brain. One of its jobs is to regulate your core temperature. It controls your heart rate, your breathing, your perspiration, directs blood flow, and blood quantity, among other things. When you’re riding in the heat, it chimes in and starts doing its magic. It maintains your core temperature plus of minus one degree. That alone is amazing, considering the outdoor temperature can range from below freezing to over 100 degrees. It keeps your core temperature at 97.6 to 99.6 degrees. WOW.

When you ride you bike, you generate heat. More heat than when your sitting on the couch watching the Tour De France. When you start getting hot, your hypothalamus tells your heart to speed up. It then changes where your blood goes in your body. Normally about 20 percent of your blood volume resides right under your skin, and 80 percent goes to your muscles, and everywhere else. When your riding in the heat, 80 percent is under you skin, and 20 percent is left to work your muscles and everything else. This is why it's impossible to perform as well in the heat – you simply don’t have enough blood to feed those bulging quads, and everything else.

Another thing that happens without our knowledge is, when it gets hot, the hypothalamus directs your body to manufacture more blood to help fill in the void left by all that blood that’s now under you skin.

It also directs the fluids in the cells of your body to go to the sweat cells and make your skin wet. Wet skin plus a little wind, equals cooling. In fact, as long as it's not too humid and you have ample fluid supply, your body’s air conditioner works pretty well. All that hot blood right under that cool skin will release the heat of your body. The blood gets cooled off a bit and returns to the core, and voila, your core gets cooler.

Everything works great, most of the time. But sometimes certain conditions can make things run amuck. Here are some.

Humidity! Humidity is your enemy. When the air is humid, and it's hot outside, the water on your skin won’t evaporate. Without evaporation, you have little or no cooling. You overheat!

Dehydration. Of course, you have to be hydrated to have enough water supply in your cells to sweat. Being dehydrated removes the water from this wonderful evaporation air conditioner, and, you guessed it. You overheat!

Here’s a little about hydration and dehydration. During a strenuous ride in the heat, you can only absorb about half the volume of fluid that you perspire out. It doesn't matter how much you drink. So you will be somewhat dehydrated after the event. The last time you performed well on a long ride in the heat, it probably had as much to do with how well you hydrated the day before the event, as it did the day of the event. So start the day before saturating all your cells in your body with fluid. A few years ago, I went to the Tour of California, and we stayed in the hotel where a bunch of the pro riders were staying. It was a small town, so after the days race, the Pro riders were walking around town. We noticed that every single one of them had a water bottle or two, and were drinking constantly. They were re-hydrating for the next days race.

Your body is amazing. It does all this stuff without us having to think about it. If we had a set of instruments and knobs, that we had to keep set right, we would all die – just because we forgot to lower the landing gear, or something.

Lastly, what happens if you push through the pain of heat exhaustion? I can assure you - YOUR HYPOTHALAMUS WILL STOP YOU! It has enormous power. You will slow down and stop, no matter how much will power you have. Trouble is if you go too far, you may carry it with you forever. Once you've had full blown heat exhaustion or heat stroke, you will always be more susceptible to the heat.

hope this helps

Steve