Using Cardio for High-Rep Workout

I�??ve had knee problems that, until recently, kept me from doing a lot of leg work. But my legs have managed to keep up with the rest of my body (keep in mind I�??m only a 175 lb. guy), and I think that it�??s probably because I do cardio workouts using elliptical training machines in interval resistance modes that have provided a decent workout for my legs.

Lately there have been a lot of articles popping up about high-rep leg workouts, and I was wondering about the possibility of using targeted cardio workouts to hit the legs and get the equivalent of a high-rep, low-weight leg workout. Precor elliptical trainers make it really easy to target body parts. What I want to try is hitting my quads on a tough interval setting for thirty minutes instead of hogging the leg press.

Does this seem viable? Is anyone out there doing it already?