That's great! Keep up the good work. Our bodies were made to walk.

I'm at 6 miles in about 1 hour and 45 minutes, once a week. Shorter distances during the rest of the week.

The problem I am having is that I seem to have reached an aerobic plateau; increasing the distance really doesn't have as much effect on my cardio-vascular fitness as I want or (per the Doc) need. It still burns calories (about 100 per mile), but the cardio training effect seems to have reached the point of diminishing returns.

My solution (still in experimental phase) is to do "Nordic Walking." I use 2 poles to push me along (sort of like cross country skiing). It uses more muscles and burns more calories. The net effect is that when I "Nordic Walk" I can only do about half my usual distance, and I end up "huffing and puffing" a lot more along the way.