A Comparison of Electromyographic(EMG) Activity & Glenohumeral Motion During Posterior Glide Mobilizations in Healthy & Stiff Shoulders

To achieve the study aims, 88 adults (44 controls, 44 with stiff shoulders) between the ages of 18-65 will be recruited. The investigators will apply a protocol based on current evidence for effectiveness of mobilizations (4 bouts of 30 sec, oscillatory gr III mobilization @1 Hz vs. 4 bouts of 30 seconds, static gr III mobilization), with interventions determined by randomized blocked assignment. Before and after the intervention, the investigators will assess levels of EMG activity of the posterior rotator cuff during a posterior glide, the force required for the mobilization to reach end range stretch, the amount of humeral head translation on the glenoid via US, and pain pressure thresholds (PPT). The data collected will allow investigators to determine the mechanisms involved in range of motion (ROM) changes and hypoalgesia produced by glenohumeral (GH) joint mobilization in both normal and stiff shoulders by evaluating the main and interaction effects of: the type of mobilization (static vs oscillatory), the magnitude of joint translation via imaging ultrasound, the EMG response of the supraspinatus and infraspinatus muscles, and changes in local and central pain processing observed via PPT testing. These data will allow investigators to evaluate whether motion improvements occur due to mechanical factors (stretch of the capsule observed via change in translation), neurophysiologic factors (change in translation associated with reduction in EMG activity), or both. Concurrent measurements of pain processing by the nervous system (local and central mechanisms) will allow evaluation of whether changes in pain processing occur following oscillatory movements, sustained movements, or both. This information will result in improved understanding of the mechanisms of action of joint mobilization, determination of the efficacy of various modes of mobilization to improve joint translation, and determination of the efficacy of various modes of mobilization to decrease pain.

Data analysis:

All data will be analyzed in aggregate form using quantitative statistics. Descriptive statistics will be utilized for demographic data including age, height, weight, gender, handedness, and side of intervention.

Groups will be measured using tests of difference based on group assignments (normal vs stiff shoulder; sustained vs oscillatory mobilization) comparing peak and root mean squared EMG activity, pain pressure thresholds, force of mobilization, and amount of translation measured via US as well as analysis of interaction effects.

All data will be analyzed using an intention to treat model, and any missing data points were replaced using imputation via means of the group.