Clinicians need accurate, simple and interpretable indicators to evaluate shoulder 3 performance, including movement speed. The primary objective was to assess the changes in mean 4 angular velocity norm and velocity variation measured by an innovative score, after rehabilitation. The 5 secondary objective was to assess the relationship between changes in both velocity variables and in 6 shoulder pain and activity limitation.

Current clinical assessment of shoulder pain focus on range of motion (RoM), clinical tests and disability, but lack information on shoulder performance. Shoulder performance is an imprecise multidimensional concept including RoM, accuracy, smoothness, and velocity. Clinicians need simple and accurate methods to measure shoulder performance.

Rotator cuff lesions are the most common shoulder pathologies. These pathologies include a wide range of soft-tissue conditions surrounding the humeral head that are grouped under the term subacromial pain syndrome (SPS). SPS is associated with pain, decreased active shoulder elevation, activity limitation and decreased quality of life. Physiotherapy is the first-line treatment for chronic SPS for pain and function.

Inertial measurement units (IMUs) have been used to assess velocity variables in people with SPS. The intra- and inter-observer reliability of kinematic temporal variables measured using IMUs is excellent in people with shoulder disorders. Most studies assessed functional arm activities rather than analytic arm elevation movements that are typically evaluated in clinical practice. Furthermore, they used rather complex kinematic temporal parameters (cumulative velocity distribution, power, moment or asymmetry scores) that can lack interpretability for clinicians. We wanted to employ accurate and clinically meaningful velocity variables used to assess arm movements during standard clinical shoulder examinations.

Inclusion Criteria:

1. Age ≥18 years,
2. unilateral SPS diagnosed by a physician using clinical tests and imaging,
3. enrolled in a usual care 4-session rehabilitation program in the PMR outpatient department.

Exclusion Criteria:

1. shoulder fracture or dislocation or shoulder surgery (with implant) <1 year previously,
2. SLAP lesion,
3. neurological pathology,
4. cervico-brachial neuralgia.

Unilateral subacromial pain syndrome diagnosed by a physician using clinical tests and imaging, enrolled in a usual care 4-session rehabilitation program in the PMR outpatient department.