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.
Miti Gupta, Amitabh Dashottar and John D. Borstad
Kurt L. Mudie, Amitabh Gupta, Simon Green, Hiroaki Hobara and Peter J. Clothier
This study assessed the agreement between Kvert calculated from 4 different methods of estimating vertical displacement of the center of mass (COM) during single-leg hopping. Healthy participants (N = 38) completed a 10-s single-leg hopping effort on a force plate, with 3D motion of the lower limb, pelvis, and trunk captured. Derived variables were calculated for a total of 753 hop cycles using 4 methods, including: double integration of the vertical ground reaction force, law of falling bodies, a marker cluster on the sacrum, and a segmental analysis method. Bland-Altman plots demonstrated that Kvert calculated using segmental analysis and double integration methods have a relatively small bias (0.93 kN⋅m–1) and 95% limits of agreement (–1.89 to 3.75 kN⋅m–1). In contrast, a greater bias was revealed between sacral marker cluster and segmental analysis (–2.32 kN⋅m–1), sacral marker cluster and double integration (–3.25 kN⋅m–1), and the law of falling bodies compared with all methods (17.26–20.52 kN⋅m–1). These findings suggest the segmental analysis and double integration methods can be used interchangeably for the calculation of Kvert during single-leg hopping. The authors propose the segmental analysis method to be considered the gold standard for the calculation of Kvert during single-leg, on-the-spot hopping.