Effect of forward head posture and visual feedback on the activity of scapular upward rotators during isometric shoulder flexion
전방머리자세와 시각적 되먹임이 어깨의 등척성 굴곡 시 견갑골 상방회전근의 근활성도에 미치는 영향
Dept. of Rehabilitation Therapy/박사
This series of two studies examined the effects of forward head posture (FHP) and real-time visual feedback of scapular movement on the activity of scapular upward rotators during isometric shoulder flexion.Study 1 examined the effects of forward head posture in the sitting position on the activity of the scapular upward rotators during loaded isometric shoulder flexion in the sagittal plane. Twenty one healthy volunteers (11 men, 10 women) with no history of pathology participated in the study. Subjects were instructed to perform isometric shoulder flexion with the right upper extremity in both the forward head posture and neutral head posture while sitting. Surface electromyography (EMG) was recorded from the upper trapezius, lower trapezius, and serratus anterior muscles. Dependent variables were examined by 2 (posture) × 3 (muscle) repeated measures analysis of variance. Significantly increased EMG activity in the upper trapezius and lower trapezius and significantly decreased EMG activity in the serratus anterior were found during loaded isometric shoulder flexion with FHP. Study 2 examined the effects of real-time visual feedback using a video camera on the activity of serratus anterior in individuals with scapular winging during shoulder flexion. Nineteen subjects, who had scapular winging, were recruited for this study. Muscle activity in the upper trapezius, lower trapezius, and serratus anterior was measured using surface EMG. The subjects were instructed to perform isometric shoulder flexion at 60° and 90° angles with and without a real-time visual feedback using a video camera to monitor scapular winging. The SIMI video motion analysis system was used to measure the displacement of a marker attached to the midpoint of the acromion in the frontal and sagittal planes. A significant main effect for shoulder flexion angle was found for the upper trapezius, lower trapezius, and serratus anterior muscles. Additionally, a significant main effect for visual feedback was revealed in the upper trapezius and serratus anterior muscles. Furthermore, activation of the upper trapezius was greater under the visual-feedback condition compared with the no-visual-feedback condition at the 60° flexion angle (95% CI of difference -3.95 to -0.67% maximal voluntary isometric contraction [MVIC]). Activation of the serratus anterior muscle was greater under the visual-feedback condition compared with the no-visual-feedback condition at the 60° flexion angle (95% CI of difference -3.63 to -2.34 %MVIC) and the 90° angle (95% CI of difference -8.52 to -3.32 %MVIC). Based on the results of two studies, it is demonstrated that correct alignment such as neutral head posture and monitoring scapular motion using a visual feedback while performing shoulder flexion are effective methods to activate scapular upward rotators.