Shoulder instability due to muscle weakness is a common problem in disorders of the upper extremities. During arm motion, the scapula acts as a dynamic base for the humeral head. To safely move the shoulder with an exoskeleton for the upper extremities a textile orthosis was developed that stabilizes the scapula against the thorax. The support level of the orthosis is continuously manually adjustable. To test the feasibility of our design and to improve the functionality of the textile orthosis, it needs to be investigated how the orthosis acts on people affected by shoulder instability. The investigators seek to explore how people with shoulder instability respond to the orthosis, and how they may benefit from the orthosis function. Therefore, the range of motion of arm elevation will be compared in different conditions: (i) without any support, (ii) with the support of a trained therapist, and (iii) when the device is engaged at the individual's optimal support level. Additionally, pilot tests will be performed to fix different parameters in our study protocol, such as the the optimal orthosis stiffness level and the ideal number of movement repetitions.

In this study, participants suffering from muscular weakness in the upper extremities, particularly the shoulder joint, will be recruited. A clear indicator for muscular weakness in the shoulder joint is a scapula alata (winging scapula). Hence, participants recruited for this study should present with a scapula alata and a limited RoM of at least one of their upper extremities.

This study is designed as a cross-over trial. Each participant will take part in an experimental session that will last approximately 2 hours. At the beginning of the experiment, the participant will be informed about the measurement and sign the informed consent sheet. Additional demographic data and level of ability will be collected in a questionnaire.

Before the measurements, participants will be fitted a textile scapula orthosis. The orthosis will be instrumented to quantify the amount of support the orthosis provides to the user. Therefore, an array of force sensors is mounted between the orthosis and the skin to measure the qualitative force distribution and its rate of change. To measure the absolute force applied to the plate, a load cell will be mounted on the orthosis fastening mechanism. All force data will be collected synchronously through a Micro-Controller board.

The participants will be equipped with reflective adhesive markers to define the reference points for the range of motion measurements, which will be done with a goniometer and photographic opto-electronic motion tracking.

Nine blocks of measurements will be conducted, lasting 5 minutes each. The remaining time in the study accounts for rest periods, the mounting and demounting of the orthosis, instructions and questionnaires. The first eight blocks will present the following treatment conditions in randomized order:

• No support (NO): the scapula is not assisted during arm elevation.
• Manual scapular assistance (SA): a trained person assists the scapula during arm elevation manually.
• Orthosis support (OS): the scapula is assisted by the textile orthosis set to meaningfully different force levels.
• Motor control task (MT): The participant reaches for a target placed at the maximum elevation height in the NO condition, once without and once with the orthosis.

While one block each is performed in the NO, SA and MT conditions, six blocks are performed in the OS condition with the orthosis set to meaningfully different force levels.

In each measurement set, participants will elevate their arms in one of two planes of horizontal rotation:

• 30° (R30) as measured from the coronal body plane.
• 80° (R80) as measured from the coronal body plane.

During arm elevation, the arm is fully extended, i.e. the elbow and wrist are fully stretched. In this position, the center of mass has the largest lever arm and therefore the maximum torque due to gravity occurs in the shoulder. One measurement set will be done in each elevation plane. During the OS condition, the orthosis will be opened between measurement sets to allow for comfort and unhindered breathing and to guarantee independence of measurement data.

After the experiment, the perceived exertion and orthosis comfort will be assessed using the Borg Scale and the Nordic Questionnaire.

Before the study, several study parameters will be determined in pilot studies with variable duration, not exceeding 2 hours. The participants in the pilot studies and the final study might be identical. During the pilot tests, participants will wear an orthosis similar to the one used in the study. Hence, effort and strain for participants will be equal or less to the final study. The pilot tests include

• Definition of optimal pressure and protocol to consistently find this pressure.
• Definition of optimal orthosis configuration.
• Definition of repeatability when orthosis is unmounted and mounted again.
• Definition of meaningful difference between pressure levels.

Inclusion Criteria:

• At least 18 years of age
• Diagnosed scapula alata (winging scapula)
• Limited range of motion of at least one of the upper extremities.
• Ability to elevate the arm at least 110° passively
• Able to sit in a chair without additional support and without leaning on the back rest.

Exclusion Criteria

• Frozen shoulder
• Osteoporosis or arthrosis of the shoulder joint
• Shoulder subluxation
• Excessive spasticity of the affected arm
• Skin ulcerations on the paretic arm or torso
• Known risk for impingement
• Orthopaedic, rheumatological or other disease restricting movements of the paretic arm
• Pain or stiffness in the shoulder joint limiting their movement
• Cardiopulmonary disease
• Psychiatric disorders or severe cognitive impairments that limit their ability to understand the study instructions