And base, meaning what you should have in your legs before doing hard efforts or intervals, say 1000 miles or so. Most enthusiasts ride year-round and so can do hard rides anytime, but starting off it's better to work up to it. There are other ways to measure besides hours, too. 150 miles/week will usually keep you with the main group on club rides. Miles is nice because most group rides are measured that way. I like to measure my weekly burn rate in calories - 7000 is a good week. Polar has an accumulated intensity function in the software for higher end HRMs. 600/week is about my steady max before overdoing it.