Exercise Bike

I recently started using a support exercise bike, and noticed a very bad back pain better - his constant, but the worst when I'm using the bike. I tried many different positions and heights of the seat, but to no avail. Why is this happening? Why put any pressure on the part of the body in a sitting position, or how to handle the machine. Why lean forward to use your back muscles to avoid falling into his face. Try to sit with you and walk back peddaling from time to time to allow your file. It sounds to hurt somewhere and somehow we have forgotten. I have horrible back pain, herniated disc, but it is a work accident in January.