"Should exercise be painful or not?" This is a popular question among physical therapists and patients alike, which is still the subject of considerable debate. Because although exercise is a proven effective treatment for chronic rotator cuff-related shoulder pain, the degree of pain during exercise is still unclear.

A pain control model is often used during exercise, describing a scale from 0 to 10, where 0 represents "no pain" and 10 represents "worst imaginable pain." Pain between 0 and 2 is considered "safe," between 2 and 5 is "acceptable," and above 5 is "high risk." In addition, pain may rise to 5 after exercise but must subside the next morning. These are general guidelines that have been applied in clinical practice, in studies and in a variety of indications in shoulder rehabilitation. 

The lack of clear evidence-based guidelines also reflects current clinical practice. Most physical therapists instructed their patients to have no pain or at least no more than acceptable discomfort. Experts in the field recently suggested using different types of exercises, depending on the acceptability of symptoms, as long as they can sufficiently challenge weakness and train to fatigue.

Physical therapists usually do not encourage patients to exercise with pain. However, there is no strong scientific basis for this fear of "training to pain." Indeed, given the principle that "hurt does not equal harm," a recent systematic review challenges this belief and suggests that short-term painful exercise is more beneficial than pain-free exercise in chronic musculoskeletal pain. Given that pain does not always correspond to tissue damage (such as a tear or tendon degeneration), other factors such as movement anxiety and central sensitization may play an important role in the development or maintenance of pain. If painful exercises are allowed with appropriate "safety cues," the physical therapist can gradually reduce the threat perception of the painful movement. If the shoulder is considered "deconditioned" and the goal is to strengthen the shoulder muscles, patients will rethink and re-modulate under the guidance of the treating physical therapist.