Cross training is important, for cardio. One of the trainers at my gym is in excellent shape, teaches step, and a lot of other classes. Anyway a few months ago he participated in a 15k race. Well his cardio level was fine for the 9.3 miles, but he hurt his foot because he didn't run properly and ended up wearing one of those boots. I think if you keep exercise fresh, and new and don't rush into a marathon first thing you can train your body so it won't get hurt. I run 3 times a week,not too fast, and not very far, but I do improve. I also take a Step class which is so different than running, and sometimes if I''m very brave I'll do a cardio jump class to mix it up. And of course there's always the dreaded treadmill, or an eliptical machine.
I agree with hsorlando. Cross training is the ultimate key for preventing injuries !
What are jump classes ?