I finally figured out why my knees hurt so bad in the past few months. It's because of this awful machine. The knee holders are hard plastic and have done a number on me. Wheels only last for three weeks. Then they have grooves that you could hurt yourself if it gets caught on them . I did and then they never get back to you with replacment parts .!!! Dont buy this ! It is poorly put together !!! My husband looked at the broken pieces and found the only thing holding that assembly together, were 3 tiny prongs! The bottom part (which hold... read full review »