Some further details would be helpful to hopefully narrow down your problem. Is this one knee that bothers you or both? How long has it bothered you? Are you aware of any injury that occurred prior to the start of the problem? Does the knee hurt? Do you notice any swelling?
It is likely that you may have some injury to the knee. An increase in fluid within the knee joint space will restrict its degree of movement. Most of the time these injuries benefit from an anti-inflammatory medicine such as Aleve and time.The longer the trouble has gone on and if you have pain , redness or swelling then you should have your doctor take a look at it.
I hope this information is helpful so far. If you respond to my questions then I might be able to be a bit more specific. Let me know if you have further questions as well. If my answer is helpful and to your satisfaction then please remember to press the "ACCEPT" button. Thank you and best Regards,
Anthony Bray MD
Well don't force it as this might injure your knees. Everyone has a certain limit to the degree of flexion of their knees. Since I can't examine you I can be sure if what you describe is a physical limit that may be within normal or something pathologic. I would recommend that you have a physician take a look at it. Preferably an orthopedic specialist. Different individuals will have different limits of flexibility. It may be that your knee flexion is limited by the anterior cruciate ligament within the knee and/or other supporting structures of the knee. Since this is both knees and there is no history of injury and no pain or swelling then I think it is just your anatomy. I would say that you should stretch within your comfort zone but don't push this to the point of pain.
I hope this helps. Good luck,