Ab. No. 97 The Effect of Different Scapular Positions on Serratus Anterior and Biceps Brachii Muscle Activity During a Forward Reach Task in Healthy Individuals

Abstract

Introduction: To study the effects of scapular protraction/retraction and neutral position on serratus anterior and biceps brachii muscle activity during a forward reach task in healthy individuals. Normal functioning of the scapula plays a key role in shoulder kinematics. Forward reaching is an integral activity for ADL’s and is a key neuro rehabilitation component. For example, posture that is usually adapted by people with stroke leads to inappropriate positioning of scapula that in turn can disrupt the muscle timing and activation slowing the rehabilitation process. Understanding the muscle activity in healthy individuals can give us a deeper insight to expand our knowledge for rehabilitation. Methods: 19 healthy subjects were selected under convenience sampling. Subjects were asked to perform a forward reach task. Three trials were taken for each scapular position. Surface electrodes recorded EMG activity of serratus anterior and biceps brachii muscle during the task. Average values were taken for analysis. Shapiro - Wilk test was done to analyse normality. The difference between the three positions of scapula (protraction, retraction and neutral) was established for serratus anterior (Fisher’s ANOVA) and biceps (Kruskal-Wallis) along with Post hoc analysis. Correlation between two muscles (serratus and biceps) was established using Spearman’s Correlation Coefficient. Results: Serratus muscle activity (F=0.135, p= 0.874) and biceps (F=0.29, p=0.7). did not achieve statistical significance among the three positions. Statistically significant correlation was found across the positions between biceps and serratus (r2 =0.58,p<0.001). Conclusion: Mean activity of serratus anterior muscle did not change with different scapular positions. However, biceps brachii muscle activity was highest with scapula being in retraction and lowest in protraction. Moderate correlation was found between SA and biceps across positions. Implications: The starting position of scapula may have implications on muscle activation and therefore can impact rehabilitation outcomes.