Maybe both…
There is a significant difference between pain that is the result of muscle work and pain that is the result of injury. Hard exercise will cause the sensation of muscle burn and may not be entirely pleasant during and shortly after exercise, but will ultimately lead to increased strength. In this instance, pain is gain.
However, if you feel that an area of your body is consistently painful during or after certain movements or activity, this pain is NOT gain. This pain is your body telling you that you are injuring it, and it would like you to stop the aggravating activity. A person receiving physical therapy for an injury should never push through their pain, with 2 exceptions: 1.) the patient is recovering from surgery – some pain following surgery is expected as you regain range of motion and strength, and 2.) the patient has been diagnosed with a chronic condition such as (but not limited to) fibromyalgia or chronic low back pain – in this case the body is responding to stimuli that are not actually injurious and is wrongfully interpreting them as painful.