I'm not using the 220 - age = MHR calculation. That is really off for me. It would put me at 173 and my real MAX, as best as I can determine is 190. So I'm using 190. I haven't been taking rest days unless the weather is bad. And in TX we usually have pretty good weather. But my running days aren't all that hard really...so I kind of count them as my rest days. I'm pretty good at staying in the 70-80% zone while running on the treadmill.