When the thermometer climbs, you know that fitness gets harder with each degree. But why? And how can you handle it?Whoambomb!A couple of days ago I stepped outside to do my running session and hello said what felt like a thermal wall. Sunshine, 30°C (86°F) and about 70% humidity. At 9 pm.It doesn't bode well for your fitness plans when you start sweating before you even hit "start" on the stop watch.After recording one of my worst times ever I sat down and researched why heat makes us perform so bad.Here's what I found.Your Heart And Getting Rid Of Heat On hot days your heart and circulatory system have extra work: dissipate heat by sending warm blood to the limbs and skin. It's a system that works like your car engine's cooling system, where cool water passes through the engine block, takes the heat along and via pipes travels to the radiator, where it cools down. Then it goes back to the engine etc. As nicely as that works for cars, in the human body the system has a major flaw: the blood used for the heat exchange has to be diverted from the muscles. That results in them getting fewer nutrients and less oxygen.On the other end of the network your heart also has to make do with less blood flowing through it during each beat. To keep your blood pressure normal it'll increase its beats per minute - before you ever got into your session. You begin with a higher heart rate and reach your target rate sooner. Despite being slower.Sweating And When It Doesn't Work But your body has a secondary cooling system, designed to aid the first. I'm of course talking about sweating.When transporting heat to the body's surface isn't enough, sweating is turned on. The heat transfers from the skin into the sweat, which will then evaporate and give off the heat to the surrounding air.But this auxiliary system comes with a caveat as well.Sweat largely consists of water (not fat, although some people dearly hope it does) and losing that water means the blood gets thicker. The thicker the blood, the worse heat transport and nutrient delivery work.In addition, that heat dissipation to the surrounding air works less the more humid it is. If the air already is full of vaporized water there's no room for yours.The Most Dangerous Enemy: OzoneIf at this point already you don't feel like calling it a day once the temperatures go off into the 80s, I still have ozone for you.As nice as it is to have that gas protecting us from the sun's radiation somewhere up there in the stratosphere, the bad it is on the surface. Down here, ozone limits your ability to breathe. The higher the temperatures, the more ozone is in the air, because ozone is produced by heat and sunlight. It's especially bad in cities, as exhausts from cars break down to the gas.Without any exaggeration, running on hot days in a city with high ozone is not doing your health any favors.What To Do?Now you know all this, but what can you do if you live in an area where it's hot for months and have no chance or inkling to train indoors?Heat will always affect your performance, make no doubt about it, but there are a couple of things you can and should do:
- As on hot days your heart beats faster before you did anything, acknowledge that you have reached high intensity despite being slower.
- Take something to drink, mineral water suffices.
- Get the right clothes. I'm no big fan of expensive running gear, but if you run in hot weather, buying "technical" clothing made from synthetic fibers is worth it. Cotton soaks up sweat, which makes dissipation harder.
- Check the ozone readings. To do that for the US, you just have to visit the AIRNow website.
- Avoid the heat altogether and run in the mornings. The temperatures will be lower and the ozone concentrations at their lowest.
- Last but not least, use sunscreen. That hasn't anything to do with your performance, but it doesn't look too good to peel like a cobra and skin cancer isn't that funny either.