The primary objective of the present study is to evaluate if a single acute BFR low load- exercise bout would reduce pain in patients with nonspecific shoulder pain and whether the potential hypoalgesia will be maintained after a 45-minute physical therapy shoulder exercise session. BFR exercise will be compared to a sham BFR exercise protocol. We hypothesize that the participants in the BFR group in will experience reduced pain and will be able to complete a scapula and rotator cuff muscles exercise loading program with reduced pain until the end of the exercise program.

Shoulder pathologies are the 3rd most common musculoskeletal condition encountered by health professionals in their day-to-day clinical practice, followed by low back pain and neck pain. It is noteworthy that approximately 40%-54% of patients report ongoing pain lasting between 1-3 years , causing a huge economic burden both on the national health care system but also to the patients. The pathologies associated with development of shoulder pain are numerous, however, in recent years the research community dealing with musculoskeletal shoulder pain has emphasized the need to break free from diagnostic terminologies that refer to precise clinical diagnosis, since such a thig is nearly impossible to happen, due to the low validity and diagnostic accuracy of the special tests available to the clinician. In addition, the need to detach from diagnostic labels becomes even more intense if one takes into account the inability to correlate symptoms and clinical status with pathological findings in diagnostic tests. Nonspecific shoulder pain is an umbrella term that includes non-traumatic musculoskeletal disorders of the shoulder.

Therapeutic exercise is the mainstay of conservative treatment and appears to be a powerful tool in the hands of clinicians to improve pain, mobility, and function of the shoulder in individuals with nonspecific shoulder pain . There are several mechanisms that are hypothesized to explain the benefits of exercise in nonspecific shoulder pain. The neuromuscular mechanism is the most frequently mentioned and is commonly explained as strengthening of the rotator cuff inhibiting pain. Other mechanisms proposed are: tissue factors (e.g. tendon remodeling, blood flow improvement etc.), neuro-endocrine-immune (e.g. exercise induced hypoalgesia, central and peripheral nervous system adaptations etc) and physiological mechanisms (e.g. improvements in self-efficacy and coping with pain etc).

The BFR method is a type of training with parallel partial restriction of arterial inflow and complete venous outflow restriction in muscle tissue that is usually combined with parallel execution of low-load resistance exercises. Blood flow restriction is achieved by using special cuffs applied to both the upper and lower extremities. During the last decade the popularity of this technique seems to be growing rapidly due to its beneficial effects on increasing muscle strength and muscle hypertrophy in healthy adults and clinical population but also its acute hypoalgetic effect on healthy population by significantly increasing the patient pain thresholds. However, to date there is only one published study examining the acute hypoalgetic effects of BFR training in a clinical population, showing beneficial adaptations in reducing pain in people with patellofemoral pain

The primary objective of the present study is to evaluate if a single acute BFR low load- exercise bout would reduce pain in patients with nonspecific shoulder pain and whether the potential hypoalgesia will be maintained after a 45-minute physical therapy shoulder exercise session. BFR exercise will be compared to a sham BFR exercise protocol. We hypothesize that the participants in the BFR group in will experience reduced pain and will be able to complete a scapula and rotator cuff muscles exercise loading program with reduced pain until the end of the exercise program.

Adults presenting with nonspecific shoulder pain will be recruited using the following eligibility criteria:

Inclusion Criteria:

• Age >18≤40 years considering that the prevalence for degenerative rotator cuff tendinopathy increases from the age of 40 and above
• Shoulder pain intensity > 4/10 NPRS when performing active glenohumeral abduction and/or isometric resistance to glenohumeral external rotation from 0° of abduction.
• Duration of symptoms > 3 weeks (to avoid an inflammatory clinical picture).

Exclusion Criteria:

• Positive drop arm test (important indication for rotator cuff tear)
• Cervical radiculopathy having a positive specific spurling test or neurological symptoms in the upper limb
• Passive deficit in range of motion (ROM) > 2 levels of motion, where according to the literature it is an indication of frozen shoulder
• Body Mass Index (BMI) > 28
• Previous shoulder surgery
• Previous humerus fracture
• Cancer
• Rheumatic diseases
• Systemic pathologies (e.g. diabetes, rheumatism, fibromyalgia)
• History of previous neurological diseases
• History of thrombosis
• Cardiovascular pathologies
• Neurological diseases
• Long-term use of corticosteroids
• Injury or surgery < 1 month related to the shoulder girdle
• Hypertension (> 140/90mmHg)
• Anti-inflammatory treatment in the last 2 weeks
• Injectable therapy (last 3 months)
• Previous experience/knowledge of the BFR technique
• Inability to write and read Greek