The purpose of this study is to directly compare the effects of four distinct interventions commonly used in the treatment of shoulder pathology on shoulder range of motion (ROM) and strength in asymptomatic shoulders:

• grade III oscillatory anterior-posterior glenohumeral joint mobilizations
• an internal rotation (IR) "sleeper" stretch
• supine upper-thoracic manipulation
• cervical spine manipulation

Research questions:

Do different interventions result in different immediate changes in shoulder ROM? Ha1: Stretching and glenohumeral mobilization will result in increased shoulder ROM Ha2: Thoracic and Cervical manipulations will result in decreased shoulder ROM Ho: There will be no differences in shoulder ROM between groups for each of the four interventions

Do different interventions result in different immediate effects for shoulder external rotation (ER) strength? Ha1: Stretching and glenohumeral mobilization will result in a decrease in ER strength Ha2: Thoracic and cervical manipulations will result in increased ER strength Ho: There will be no differences in ER strength between groups for each of the four interventions

Do different interventions result in different immediate effects for shoulder electromyographic (EMG) activity? Ha1: Stretching and glenohumeral mobilization will result in a decrease in EMG activity Ha2: Thoracic and cervical manipulations will result in increased EMG activity Ho: There will be no differences EMG activity between groups for each of the four interventions

Based on pilot data, the apparent effect sizes ranged from .57 - .78. With the ɑ = .05 and 1-β = .80, G-power software for a 4 group ANOVA yields a sample of 20 participants per group. To account for possible sample variations and participant drop-outs, a sample of 24 per group will be enrolled. Based on the study design of a randomized cross-over study, where each participant will receive two of the interventions, a total sample of 48 individuals will be enrolled.

Once a participant is cleared to participate, all individuals will undergo the following tests:

External Rotator Strength Test Strength of the external rotators (infraspinatus) will be measured by a blinded examiner using a hand-held dynamometer (Micro-FET 2, Hoggan Health Industries, Salt Lake CIty, UT). The dynamometer will be placed on the high threshold setting and the force recorded in Newtons. The strength measurement will be taken with the participant in the prone position with their shoulder abducted 90 degrees and 80 degrees of external rotation with the elbow bent to 90 degrees. Abduction (ABD) and elbow flexion ROM positioning will be assessed using a goniometer, and the shoulder external rotation ROM will be measured using the iPhoneX. To ensure consistent placement, the researchers will place a mark 10 cm proximal to the medial epicondyle of the humerus. This mark will be aligned with the edge of the table in order to allow for adequate clearing of the arm and dynamometer while completing the test. A second mark will be placed on the distal end of the radius, using the radial styloid process as a reference. The distal edge of the dynamometer will be placed at this mark. The testers knee will be positioned behind the participant's elbow to ensure there is no compensation and activation of other muscles. At the start of the test the participant will be instructed to resist the pressure applied by the tester. The tester will apply their force progressively over 5 seconds while the participant maximally resists against the dynamometer plate. Two pretest and two post-test measurements of strength will be obtained, with the greater measurement used for data analysis.

Posterior Shoulder Tightness Posterior shoulder tightness (PST) will be measured by blinded examiners with the participant side lying with hips and knees flexed to 45 degrees. The non-tested humerus will be placed behind the participants head with half of their humerus off of the plinth. The participants' arm being tested will be placed so that the humeral condyles will be stacked perpendicular to the plinth with the olecranon facing posteriorly in relation to the participants' body. The participant's arm will be marked 5cm proximal to the lateral epicondyle, where an independent examiner will place the top of the iPhoneX to measure PST in degrees. The Level in the Measure application, manufactured by Apple's arkit via iOS 13.2.3, will be used to measure horizontal adduction and quantify PST. The tester will be blinded from the results of the PST measurement. The arm being tested will be gripped by the tester just distal to the humeral condyles. The scapula will be stabilized in retraction throughout the test. The test will be completed and the measurement will be recorded when the tester is no longer able to stabilize the scapula or the movement ceases. Two trials will be performed by the tester with a 10 second rest between trials.

Internal Rotation ROM Internal rotation range of motion will be measured by a blinded examiner with the participant in the prone position, shoulder abducted to 90 degrees, with a bolster under the mid-humerus to keep the glenohumeral joint in the neutral position. A mark will be placed on the participants arm 5cm distal to the medial epicondyle on the ventral forearm where the top of the iPhoneX will be placed to measure internal rotation range of motion in degrees. Two testers will be used to complete the test. One tester will apply stabilization by placing their elbow atop the scapula, their forearm on top of the participant's humerus, and take the participants through the motion. The other tester will hold the iPhoneX and record the final measurement. The test will be completed when the scapula begins to rise from the table or no further motion is felt. The tester performing the motion will be blinded to the measurements being taken. Two trials will be taken on the right upper extremity.

The iPhoneX (iOS 13.2.3) will be used as an inclinometer using the Level in the Measure application that is pre-downloaded on the iPhoneX. In this study, the smartphone inclinometer application that is available to iPhones for purchase was used.

EMG of the Infraspinatus Pre-post intervention activity of the infraspinatus muscle will be assessed with surface EMG during a maximal voluntary isometric contraction (MVIC). Before placing the electrodes on the participants, the area will be thoroughly cleaned with an alcohol wipe. A single, Norotrode 20 electrode will then be placed over the muscle belly of the infraspinatus. The Delsys EMGworks acquisition software will be used to obtain all EMG data. The electrodes will be sampled at a rate of 1926 samples/s. Maximal Voluntary Isometric Contraction (MVIC) will be recorded simultaneously with the isometric strength testing. The MVC for each participant consists of a 5s hold in the standard manual muscle testing(MMT) positioning.

All EMG data will be prepared and collected by an assessor blinded to the assigned intervention, and will be analyzed using the Delsys EMGworks Analysis software.

Randomization:

Prior to enrollment, using paired, block randomization, a set of 48 group assignments will be prepared and placed in sealed, opaque envelopes by an individual not involved in the data collection process.

The participants will be assigned to two of the four different intervention groups: posterior shoulder mobilization, cervical manipulation, thoracic manipulation, and a self-applied sleeper stretch technique.

All participants will select an envelope at the time of enrollment, and only reveal the contents to the examiner preforming the intervention. The first intervention will be applied at the first research session, and the second intervention will be applied during a second session approximately one week later.

Data Analysis:

Baseline and participant demographic data will be analyzed and reported using descriptive and measures of central tendency.

Interaction and main effects for Internal rotation ROM, posterior shoulder tightness, external rotation force, and infraspinatus EMG activity x intervention will be assessed with repeated measures ANOVAs and post hoc testing.

Inclusion Criteria:

• Participants will be included in this study if they:

  • are between the ages of 18 and 55
  • have no history of shoulder, neck, or upper back dysfunction.

Exclusion Criteria:

• Individuals will be excluded if they report having any of the following conditions:

  • shoulder, neck, or upper back pain;
  • prior shoulder, neck or upper back surgery;
  • previous injury to shoulder, neck, or thoracic area;
  • active inflammatory disease process in treatment area;
  • osteoporosis;
  • signs and symptoms of a nerve root pathology/radiculopathy (dermatomal sensory changes, myotomal weakness, reflex changes);
  • upper motor neuron lesions/spinal cord pathology;
  • local infection;
  • active or history of cancer;
  • long term corticosteroid use;
  • systemically unwell;
  • systemic hyperlaxity;
  • known connective tissue disease;
  • known abnormalities of the spine;
  • disturbance of bowel or bladder;
  • coronary artery disease;
  • unstable upper cervical spine;
  • positive testing for vertebral basilar insufficiency (VBI);
  • spondylolisthesis;
  • spondylosis;
  • pregnancy or recent pregnancy;
  • nervous system dysfunction;
  • has received physical therapy for related shoulder, neck, or upper thoracic dysfunction;
  • blood clotting disorder;
  • receiving workman's compensation or involved in an active lawsuit;
  • currently taking fluoroquinolones (Cipro, Factive, Levaquin, Avelox, Noroxin, Floxin)
  • any other known contraindication to manual therapy The study will not include adults unable to consent/persons with cognitive/developmental disability, individuals who are not yet adults, pregnant women, or prisoners or other detained individuals.

IPD will be made available in de-identified form upon request

outcomes assessor blinded to group allocations