Changes in Body Segment Inertial Parameters with Weight Loss

Abstract

Overweight and obesity afflicts ~65% of the U.S. population and more than 1 billion people worldwide. Virtual experiments can be performed using forward dynamic movement simulations to explore the biomechanical benefits of weight loss. These studies require estimates of changes in body segment inertial parameters (SIPs) with weight loss. Unfortunately, these estimates are currently unavailable. PURPOSE: To determine changes in segment mass, center of mass (COM) position, and radius of gyration of the shank, thigh, and trunk with weight loss in obese Caucasian men. METHODS: Nineteen men of age 43.6 ± 7.5 years (mean ± standard deviation) and height 177.3 ± 6.9 cm were evaluated. Body mass and BMI were 102.7 ± 13.6 kg and 32.6 ± 3.2 kg/m2, respectively, before weight loss. Magnetic resonance imaging (MRI) was used to estimate SIPs using validated techniques. Transverse MRI scans of 10mm thickness were acquired along the length of the body with a spacing of 50mm between scan centers. Tissue discrimination in each scan was completed using optimal threshold values of pixel brightness for adipose tissue, muscle, organs, and bone using automated procedures with manual correction of obvious artifacts. SIPs were determined before and after weight loss using these scans, published tissue densities, and established mathematical relations. RESULTS: Subjects lost 14.1 ± 3.3 kg or 13.7 ± 2.4% of initial body weight (p<0.05). Segment masses all decreased with weight loss (p<0.05) including the shank (−7.7 ± 3.4%), the thigh (−11.9 ± 3.0%), and the trunk (−14.5 ± 5.4%). COM position of the thigh moved distally (p<0.05) with weight loss (2.2 ± 1.0%) while the COM position of the shank (0.2 ± 2.0%) and trunk (−1.0 ± 4.7%) did not change significantly (p>0.05). Radius of gyration of the trunk decreased (p<0.05) with weight loss (−1.6 ± 3.6%) while the radius of gyration of the shank (0.0 ± 0.8%) and thigh (0.3 ± 1.4%) did not change significantly. CONCLUSION: Changes in SIPs with weight loss differed between segments and parameters. These changes can be used in forward dynamic simulations to explore the biomechanical benefits of weight loss on movement kinematics and kinetics. Supported partially by the Wake Forest University Claude D. Pepper Older Americans Independence Center (P30-AG21332).