Heat Stroke: How to Cycle in Hot Weather

Daily temperatures in Sacramento rarely dip below 90º in July and August — an 80º day is considered chilly here. Recently we've have temperatures pushing 110º, a rarity for Sacramento, but not unheard of. I see a 10 to 15% degradation in my performance when the temperature is above 90. So I'm wondering if there's a way to really chip away at that degradation and get up to 100% even in the hea
t of the summer.

The question is, how do you maintain your training schedule in that heat? Its not easy! There are obvious tips that occur to me off the top of my head:

• Ride early;
• Ride at night;
• Drink plenty of water and electrolytes;
• Eat salty food;
• Wear a hat under your helmet and wear plenty of sun screen; and
• Practice, practice, practice!

...to name a few. Conspicuously off the list is taking breaks, even in the shade. You'll see that moving is key to remaining cool while cycling on a hot day. And that's because moving makes you sweat.

According to the on-line magazine Active, there are four ways your body dissipates excess muscular heat, making prolonged summer cycling possible: "... conduction, convection, radiation and evaporation." Although the article doesn't come out and say it, sweating is the key to each of these. And that means two things: moving and hydration.

Moving increases your exposed skin, aiding radiation. Moving creates its own wind, aiding in evaporation. Moving brings hot fluids from your core to the outside, aiding conduction and convection. Most importantly, moving makes you sweat which then evaporates off your skin — and evaporation is the key to the process:

Sweat is mostly water, and molecules in water are in constant motion. The temperature of water gives us an idea of the average motion of the water molecules. Each water molecule bounces off its neighbors, sometimes gaining energy from the collision, and sometimes losing energy to other molecules. At any given time, however, some molecules carry more energy than others. That is, most molecules will have temperatures close to the average, but some will be much hotter or colder than the average on occasion. 

When water evaporates, some of the molecules fly out of the liquid into the air. Hotter molecules have more energy and are moving around faster, which means that they are more likely to fly away and leave the cooler molecules behind. The evaporating molecules in your sweat actually carry the heat of your body into the air. [From American Institute of Physics.]

The lesson is: taking a break may be necessary if you're fatigued, but its not going to cool you off on a hot day!

Hydration is equally important in this process: you can't sweat if you're dehydrated:

While sweating is necessary to help cool the body, the production of sweat comes at the expense of your body fluids. As much as 1 to 2 quarts of fluid per hour may be lost as sweat while cycling in very hot weather. To help you understand the seriousness of this, the loss of as little as 2 to 3 percent of your body weight due to dehydration can impair exercise performance. [From Active, p2 for additional tips.]

My large water bottles hold 25 oz. each. Since, according to this estimate, I'm losing 32 to 64 hours per hour, I have to drain both water bottle each hour I ride. That's a LOT more water than I usually drink!

So for me, for now, I'm going to try to drink a LOT more water on my hot-weather rides.

Love,
Your Bear