Scapula kinematics differ by body mass index

The biomechanical changes due to increased arm mass in individuals with high body mass index (BMI) may lead to altered scapular motions at the shoulder joint. Scapula kinematic alterations are often associated with shoulder pain and pathology, and if present in overweight or obese individuals could impact shoulder health. The purpose of this study was to examine if scapula biomechanics differ between groups separated by BMI. Three-dimensional scapula kinematic data during arm elevation were collected on 41 subjects, and then compared between higher BMI (BMI ≥ 27; n = 10) and lower BMI (BMI ≤ 23; n = 10) individuals, both with and without holding a 1.36 kg (3 lb) weight. Data were analyzed with a mixed-model ANOVA with Group and Elevation Angle the between- and within-subject factors, respectively. The higher BMI group had significantly greater scapula upward rotation than the lower BMI group at 120° for both the unweighted and weighted tasks. Individuals with higher BMI in this study had altered scapulothoracic movement, which may be a strategy to better manage increased arm mass. With increased scapula upward rotation also reported in groups with rotator cuff tears, this study supports the potential link between high BMI, kinematics, and rotator cuff pathology.