I initially heard about this chair after speaking to my doctor about my knee problems. I am disabled and at times i find it hard to do anything to ease my pain, other than pain pills. I purchased a recumbent bike and at my doctors request and I also purchased this chair. I would not advise its use to the average healthy user seeking a comfortable chair, but if you are suffering from knee injuries I would highly advise you to try this chair. All though it isn't comfortable to sit in for 3+ hours it is comfortable to sit in for short periods of time and most importantly it helps properly position your knees. I would often sit with my knees in odd positions, because my height and most chairs I sit in would extend my feet forward. My doctor informed me that my poor posture and particularly my knee position, in relation to my feet, while I sit add to my pain. Since I purchased my Cando Ball Office Chair. I have enjoyed the reduced pain periods and find myself needing less pain pills. If you have knee problems I would highly recommend this product.