Many people think of the bicycle as some sort of exercise equipment. But it was actually invented as a labor-saving (and time-saving) device. On a bicycle, you need a fraction of the time and energy that you would expend to walk or run the same distance. It's been called the most energy-efficient form of travel. So why do we often associate bicycling with exertion and sweat?
Well, if you are trying to go as fast as you can, then you will put a lot of effort into it. And it's tempting to go fast - we are programmed to save time and be competitive in our hectic lives. Personally, I am constantly running late (why is it so hard to get up in the morning??) so I try to hurry anywhere I can. Plus, a cyclist often feels pressured to keep up with car traffic as much as we can. It's easier to choose your own pace on a quiet street or on a bicycle lane, track, or path.
But ultimately, your level of exertion is your choice. Pick a maximum level and let that determine your speed. It's not as easy as it sounds! There's a strong urge to sprint to make it through a green light, or to pedal harder up a hill rather than climbing slowly in a low gear. But I remind myself that it's worth it to take it easy. I might gain a few minutes by rushing, but I would lose them in cleanup time once I reached my destination. I would get even sweatier walking to the train, and I'm not going to give up all the conveniences of the bicycle just to drive in an air-conditioned car.
I'm not alone in advocating a moderate pace. Dottie from Let's Go Ride a Bike discovered the benefits of slowing down, too. And there's even a Slow Bicycle Movement that touts all the benefits of slowing down. I also see plenty of Atlanta bicyclists taking it easy in the heat.