Scapular kinematic alterations during arm elevation with decrease in pectoralis minor stiffness after stretching in healthy individuals

Abstract

Background: Pectoralis minor tightness may be seen in individuals with scapular dyskinesis, and stretching is used for the treatment of altered scapular motion in sports and clinical fields. However, few researchers have reported on the effects of pectoralis minor stiffness on scapular motion during arm elevation. This study investigated whether an acute decrease of pectoralis minor stiffness after stretching changes the scapular motion during arm elevation.

Methods: The study allocated 15 dominant and 15 nondominant upper limbs in healthy men as control and interventional limbs, respectively. In the intervention limb group, the shoulder was passively and horizontally abducted at 150° of elevation for 5 minutes to stretch the pectoralis minor muscle. Before and after stretching, an electromagnetic sensor was used to examine 3-dimensional scapular motion during abduction and scaption. Ultrasonic shear wave elastography was used to measure pectoralis minor stiffness before and immediately after stretching and after arm elevation.

Results: In the interventional limb, pectoralis minor stiffness decreased by 3.2 kPa immediately after stretching and by 2.5 kPa after arm elevation. The maximal changes in scapular kinematics after stretching were 4.8° of external rotation and 3.3° of posterior tilt in abduction, and 4.5° of external rotation and 3.7° of posterior tilt in scaption. Upward rotation in abduction or scaption did not change.

Conclusions: Stretching for the pectoralis minor muscle increases external rotation and posterior tilt of the scapula during arm elevation.

Keywords: Shoulder; biomechanics; elastography; muscle stiffness; pectoralis minor muscle; physical therapy; stretching.