Effect of changes in pelvic tilt kinematics on electromyographic activity of the serratus anterior, trapezius, and thoracic posture in individuals with rounded shoulder

Background and purpose To examine the effect of induced posterior pelvic tilt (changes in pelvic kinematics) on serratus anterior, lower trapezius, and upper trapezius electromyographic activity, and thoracic posture during arm elevation in individuals with rounded shoulder. Materials and methods Thirty healthy volunteers (26 male and 4 female participants) with rounded shoulder, their mean age 22.80±3.2, BMI 23.51± 3.9 were evaluated for both thoracic and pelvic posture using a 9-camera, 3-dimensional motion capture system (Vicon Nexus version 2, Oxford, UK), serratus anterior, lower trapezius, and upper trapezius electromyographic activity. The measurements were recorded in different six experimental conditions while inducing posterior pelvic tilt during arm elevation. For the six experimental conditions involving arm elevation, repeated measures analysis of variance within-subjects was used to examine the changes in electromyographic activities of lower trapezius, upper trapezius, and serratus anterior due to pelvic kinematics’ changes whereas paired t-tests were used to examine the changes in the thoracic posture in response to pelvic kinematics’ changes and to compare the pelvic tilt angle between the habitual relaxed position and the induced posterior tilt position. Results Upper trapezius, serratus anterior, and lower trapezius electromyographic activity significantly increased in response (changes in pelvic kinematics) induced posterior pelvic tilt (35:40%) of the maximal posterior pelvic tilt, although there were no apparent alterations in thoracic posture. (p>0.05). Conclusion Induced posterior pelvic tilt, (35:40%) of the maximum, resulted in an increase in the electromyographic activity of serratus anterior, lower trapezius, upper trapezius, which reflects that changes in pelvic kinematic could alter scapular muscles activity, so comprehensive examination of pelvic posture is required in both preventive and treatment programs of shoulder complex injuries. Meanwhile, no significant effect was reported on thoracic posture.