The aim of this research was to investigate which shoulder abduction angle (30°, 90°, 150°) during shrug exercise is superior for (1) activating the scapular upward rotators and (2) improving scapular and clavicular position in subjects with scapular downward rotation impairment. Twenty subjects performed shrug exercises at three different shoulder abduction angles (30°, 90°, 150°) which were obtained and maintained actively. Surface EMG data were collected from the levator scapulae (LS), upper trapezius (UT), lower trapezius (LT), and serratus anterior (SA) during shrug exercises. Scapular downward rotation index (SDRI) and clavicular tilt angle (CTA) were measured immediately after each shrug exercise. Oneway repeated-measures analysis of variance was used to determine the significance. UT muscle activity was greater at 90° and 150° than at 30° of shoulder abduction. UT/LS muscle activity ratio was greater at 90° than at 30°. LT and LT/LS increased as shoulder abduction angle increased. SA was greater at 150° than at 30° or 90°. SA/LS was greater at 150° than at 30°. SDRI was lower at 90° and 150° than at 30°. CTA was greater at 90° and 150° than at 30°. In conclusion, shrug exercises at 90° or 150° of shoulder abduction angle may be advocated to activate scapular upward rotators, decrease SDRI, and increase CTA in patients with scapular downward rotation impairment.
Keywords: Scapular downward rotation impairment; Scapular upward rotators; Shrug exercise.
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