Resting Position Variables at the Shoulder: Evidence to Support a Posture-Impairment Association

BACKGROUND AND PURPOSE: A relationship between posture and impairment at the shoulder is theorized, but not supported by evidence. It is proposed that posture and impairment are not directly related, but linked by movement dysfunction. The purpose of this analysis was to explore the relationships among posture, pectoralis minor muscle length, and movement alterations at the shoulder. SUBJECTS: Subjects who were asymptomatic for shoulder pathology were divided into 2 groups of 25 subjects each based on normalized pectoralis minor muscle resting length. METHODS: Scapula orientation, thoracic kyphosis, and pectoralis minor muscle lengths were measured, and ratios and indexes of postural variables were calculated. All variables were analyzed for correlations and group differences. RESULTS: Significant group differences were demonstrated for several posture variables, including thoracic spine kyphosis and scapular internal rotation. The distance from the sternal notch to the coracoid process demonstrated the highest correlation with pectoralis minor muscle length. DISCUSSION AND CONCLUSION: The findings indicate a relationship between posture and pectoralis minor muscle length and support a proposed model linking posture, an anatomical variable, movement dysfunction, and impairment.