A Comparison of Electromyographic Activity & Glenohumeral Motion

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.

All outliers, defined as data points beyond the 95th percentile and identified as outliers during analysis in SPSS, will be Winsorized to minimize the effect of potentially spurious outliers via replacement with the highest non-outlier obtained value for the group.

Descriptive statistics including means, ranges and standard deviations will be assessed for each group condition.

Data will be assessed for the required assumptions for parametric testing/ Analysis of variance(ANOVA) including Mauchly's test of sphericity and the Shapiro-Wilk test of normality. Data not meeting the required assumptions will be assessed with the appropriate non-parametric equivalent test.

Aim 1 will investigate the relationships and within and between group differences in rotator cuff activity (EMG) and posterior glide mobility and mobilization force in the glenohumeral joint in individuals with stiff and normal shoulders based on joint mobilization type.

To analyze within subjects main effects, interaction effects, and second order interaction effects of group and mobilization condition on the DV, three-way between-between-within mixed ANOVAs will be used.

IV: shoulder condition stiff vs normal; oscillation vs static posterior glide; time.

X Repeated measure Dependent variables(DV)s: EMG, US translation, force In the presence of significant three way interactions, post hoc testing to determine simple two way interaction effects will be performed using separate two way ANOVAs Univariate testing will be utilized to determine the presence of simple main effects.

Post hoc analysis will utilize pairwise comparisons in the presence of significant main effects. Bonferroni correction will be utilized due to multiple tests, with comparisons within each simple-simple main effect considered a family of comparisons.

To investigate the relationships between rotator cuff activity (EMG) and posterior glide mobility in individuals with stiff and normal shoulders, point bi-serial correlation will be utilized to assess for meaningful relationships between the following variables:

Mobilization condition x change in EMG, US, force Group (stiff vs control) assignment x change in EMG, US, force Aim 2 will investigate the within and between group differences and relationships between changes in PPT and type of mobilization (static, oscillatory) in individuals with stiff and normal shoulders.

Between group differences will be assessed via ind. t-tests, using the dichotomous independent variables (IV) static vs. oscillatory mobilization, and the DV of PPT measures.

Within group differences will be assessed via paired t-tests, using the dichotomous IV static vs. oscillatory mobilization, and the DV of PPT measures.