The envelope of a joint, especially the knee refers to the amount of load it can take before injury occurs. This concept is important when having a knee replacement. You want an implant that can hold up under everyday wear and tear. If you are more active than the average adult, then a different type of implant may be needed.
You can actually increase the envelope...in other words you can increase how much load or stress the knee can take before it's overloaded. You can do this by losing weight (if you are overweight). You can also strengthen the muscles around the joint and increase your flexibility as two other ways to increase the envelope of function.
Doctors advise against "putting up with the pain." Many times a patient who tries to wait it out becomes weaker and weaker. Before you know it, he or she is doing less and less. They become less flexible. They may even gain more weight because of the inactivity.
When it comes to knee pain and rehab, there's more than one way to "push the envelope" so to speak.