The purpose of this study is to measure the amount of movement between the bones of the shoulder joint when mobilization techniques are applied by a physical therapist.

The purpose of this study is to image the articular joint movement of the glenohumeral joint utilizing ultrasound imaging (USI). Specific aims include: 1) measurement of the distance between the articular surfaces at rest; 2) measurement of the distance between the articular surfaces during manually applied glides of those surfaces; and 3) analysis of any association between the amount of glide and reported joint mobility, force application, or joint position.

Subjects will be recruited from a population of convenience. After consenting to participate, eligible subjects will complete a demographic questionnaire and pretesting of scapular and shoulder mobility. Two days of testing will be scheduled. On the first day, three grades of glenohumeral mobilization will be applied in the following directions: distraction, posterior and inferior. A handheld dynamometer will measure force; ultrasound imaging will record glenohumeral joint position. Each grade and direction will be repeated three times on the right and the left shoulder. On the second day, the mobilizations will be repeated. Measurements of humeral movement will be calculated from the ultrasound images.

Inclusion Criteria:

• asymptomatic subjects with no history of neck, shoulder, or arm pain; full active pain free range of motion at the cervical spine and shoulders

Exclusion Criteria:

• neuromuscular or musculoskeletal disorders; connective tissue disorders such as rheumatoid arthritis; inflammatory conditions such as Crohns disease; Down's syndrome; Marfan's syndrome; medically diagnosed hypermobility; history of neck, shoulder or arm trauma, pain, or surgery including dislocation and rotator cuff tears; pregnancy; and metal implants