I started primarily for environmental reasons, and that's more than half the reason I continue. But it also keeps my blood pressure down better than medication. I have no doubt that it's adding years of healthy living to my lifespan. And it's fun, and when I get to where I'm going, I feel great and full of energy.
When I don't ride, I feel like a slug all day, I'm not very productive, and after several days of not riding my blood pressure is significantly elevated.
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Work: the 8 hours that separates bike rides.