my gravity strider hurts my knees and hips

w0nderkitten

I am wondering if I am positioning my feet correctly. Can anyone give any advice? I have old knee injuries and have had hip problems on and off with exercise since childhood so the joint doesn't always roll easily but it didn't hurt when I first started. The only change I can think of is doing it for 30/35 minutes as opposed to 20 like I did at first.