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Date Permissions Signed


Date of Award

Fall 2017

Document Type

Masters Thesis

Degree Name

Master of Science (MS)


Health and Human Development

First Advisor

San Juan, Jun G.

Second Advisor

Jantzen, Kelly J.

Third Advisor

Suprak, David N. (David Nathan)


Shoulder muscle dysfunction can lead to glenohumeral incongruity and can negatively affect glenohumeral joint stability. Fatigue of the infraspinatus could affect joint stability. The purpose of this study was to examine the effects of fatigue on the muscle activation of the infraspinatus, specifically, the motor evoked potential (MEP) amplitude, peak-to-peak duration, and activation latency of the MEP. Eighteen healthy college age students (eleven males, seven females) participated in this study. Subjects were screened for history of head trauma, shoulder pain, shoulder surgery, any neuromuscular disorders and potential conditions that might place them at a higher risk for adverse effects of transcranial magnetic stimulation.

Subjects were instrumented with two electrodes on the infraspinatus. Maximal voluntary contraction of humeral external rotation was recorded before and after fatigue. The subjects held their right arm parallel to the floor at 45° of scapular abduction to induce muscle activation of the infraspinatus during stimulation. Stimulations were given before and after fatigue over the motor cortex directly involved with the infraspinatus. The fatigue protocol consisted of the subject holding onto a TheraBand and performing external rotations until fatigued.

Paired t-tests were used to compare MEP amplitude, peak-to-peak duration, and activation latency before and after fatigue. Following fatigue, there was a significant effect on peak-to-peak duration (p = 0.0005; r = -.50). No significance was found in MEP amplitude and muscle activation latency. In conclusion, peak-to-peak duration increased but it is unknown how this might change muscular activation in a fatigued state.





Western Washington University

OCLC Number


Subject – LCSH

Shoulder--Muscles--Fatigue; Joints--Hypermobility




masters theses




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