The role rehabilitation plays in the management of patients with lateral epicondylalgia (LE) remains elusive secondary to high recurrence rates. Addressing scapular muscle deficits may be important in the rehabilitation of patients with LE. However, it is unknown if scapular muscle impairments exist in a working population of patients with LE. The purpose of this dissertation was to assess scapular muscle strength and endurance in a working population of patients with LE. Clinical scapular muscle assessment tools are limited in their ability to isolate specific muscles. Rehabilitative ultrasound imaging (RUSI) is a potentially useful tool but few studies have investigated its utility. Absolute muscle thickness measurements were obtained on healthy individuals for the lower trapezius (LT) and serratus anterior (SA) under three conditions (arm at rest, arm elevated with a low load, arm elevated with a high load). For both the LT and SA, a significant distinction could be made in muscle thickness between rest and a loaded condition but not between the two load conditions. Furthermore, excellent reliability was demonstrated for both muscles. It is unknown whether arm dominance plays a role in scapular muscle assessments. Therefore, healthy individuals between the ages of 30 and 65 were recruited to compare the effect of arm dominance on scapular muscle strength, endurance, and change in thickness measured by RUSI. Results indicate that arm dominance does significantly affect some measures of scapular muscle strength and endurance. However, the differences between the dominant and non-dominant limbs were not beyond measurement error. Scapular muscle strength, endurance, and change in muscle thickness of the LT and SA were assessed in 28 patients presenting with signs and symptoms consistent with LE. LT strength, SA strength, middle trapezius strength, endurance, and change in SA thickness were significantly less in patients with LE compared to matched controls. SA and LT strength were significantly less in the involved limb compared to the uninvolved limb in patients with LE. The results suggest that assessing scapular muscle endurance as well as LT and SA strength is indicated when evaluating patients with LE, and the results should be compared to normative data.

Purpose: The upper trapezius to serratus anterior muscle activation ratio is essential for optimal shoulder function. An alteration of this ratio, specifically a decrease in upper trapezius and increase in serratus anterior activation, is a main area of focus in shoulder rehabilitation (Kibler, 1998; Paine & Voight, 1993). Electromyography (EMG) biofeedback has been shown to be an effective rehabilitation technique to address many musculoskeletal disorders but there is limited research on the retention of improvements seen with EMG biofeedback (Ma et al., 2011; Lim et al., 2014; Weon, et al., 2011). The purpose of this study was to determine if EMG biofeedback can be used to improve scapular control by decreasing the upper trapezius to serratus anterior activation ratio. A secondary purpose was to determine if these predicted improvements in the ratio can be retained beyond the timeframe in which the treatment is provided. Methods: Twenty college aged (age=21.75±1.77) subjects (10 males, 10 females) volunteered to participate in this study. Subjects were randomized to the exercise only group or EMG biofeedback group. The exercise only group performed three exercises twice a week for four weeks with supervision. The EMG biofeedback group performed the same exercises twice a week for four weeks with the addition of watching EMG biofeedback on a computer monitor with the instructions to decrease the upper trapezius activation and increase the serratus anterior activation by adjusting the corresponding lines on the monitor. The percent maximal voluntary contraction (MVC) for each muscle during each exercise was measured on visit one, visit nine (after the four weeks of practice) and visit ten (after a two-week retention period). The ratio and the individual muscle changes were analyzed using multi-factor ANOVAs against group, exercise, and group by exercise interaction. Results: There was no significant effect of any of the variables on the ratios visit one to visit nine, nor when comparing visit nine to visit ten. The was a significant effect of group on the upper trapezius when comparing visit one to visit nine (p=0.007) with no effect seen comparing visit nine to visit ten. There was also a significant effect of group on the serratus anterior activation for both visit one to visit nine (p=0.000) and visit nine to visit ten (p=0.001). Conclusion: EMG biofeedback did not decrease the upper trapezius to serratus anterior activation ratio, but the individual muscle activation changes indicate that EMG biofeedback is effective at altering muscle activation rates in individual muscles and that those changes can be retained beyond the timeframe of the intervention. Additional research is needed with more subjects and in populations with shoulder pathologies to further investigate the effectiveness of this concept.