I have run a number of marathons in past years and have always enjoyed running and training. However after many miles and years of training and two minor knee surgeries and avoiding running for a couple of years I was itching to get back to running. I found that even after short runs I would need a couple days to recover because my knees were real tender. Still itching to stay at it but maybe cross train a little better I came across the zero runner. The first time I tried it I felt very awkward. I went back to my local fitness equipment store and tried it again. This time it felt a little better. So I decided to purchase the ZR7. I consistently trained just on this piece of equipment for six months and found I could go day after day with out any hip, knee, ankle or foot pain. During that time I went from 20 to 30 minutes to at times over 2 hours for a workout. Well over 50lbs lighter now I recently had one of my boys ask me to go on a slow ten miler on the road. I said sure why not. Well the run went great. The next day I was sore mainly muscle fatigue but felt good, rested and did not run. The next day I got back on my zero runner for a little over an hour and felt great. I will no longer hit the road day after day as I did in past years training for marathons. Using the zero runner has improved my cardio and overall muscle strength. Highly recommend this piece of equipment from Octane Fitness. So much so I am looking to upgrade to the best zero runner they produce!