i've always wondered this, maybe someone can help.....i use to run in gym class and it seemed to keep my legs in great shape. living in the city I don't really want to run around town and going to the gym just isn't my thing. so I was wondering if running in place is any help? i'm sure it's not as good as a full run but what effects does it have? should I try and run in place for 20 minutes or something?