I know it's a great way to get in shape. But I was just wondering how I should go upon exercising on it. I don't know how hard to ride, how far, or how long etc. Like I tend to burn out if I go too fast, and if I go long distances I tend to keep a pace. What should I be feeling to know that I'm riding vigorously enough and when I should start slowing down a bit to not get really tired. Any input would be great.