Introduction Results Browning, R.C., Baker, E. A., Herron, J.S., Kram, R. Effects of obesity and sex on the energetic cost and preferred speed of walking. Journal of Applied Physiology 100: , Rao G, Amarantini D, Berton E, Favier D. Influence of body segments’ parameters estimation models on inverse dynamics solutions during gait. Journal of Biomechanics 39: 1531–1536, DIFFERENCES IN JOINT TORQUES DURING WALKING DUE TO STANDARDIZED VS. SUBJECT-SPECIFIC SEGMENTAL INERTIAL PARAMETERS, MAGNITUDE OF OBESITY, AND WALKING SPEED. Ann Marie Tullock, Patrick M. Rider, John D. Willson, Zachary J. Domire, Jessica B. Van Meter, Paul DeVita Department of Kinesiology, East Carolina University, Greenville, North Carolina Knee joint compression forces at baseline (solid), 6 months (dashed) and 12 months (dotted). First and second maximum forces reduced 18% and 24% (α, p<0.05) at 6 months but were unchanged at 12 months. 20 adults (44 yrs) with BMI values between 18 and 44 kg/m 2 participated after providing written informed consent. Dual x-ray absorptiometry (DXA) was used to define subject-specific pelvis, thigh, shank, and foot segments along with subject-specific BSIP values. Hip and knee joint torques were calculated using both standard (from Dempster) and subject-specific BSIPs while walking at 1.53, 1.70, and 2.06 m/s. Differences between maximum hip and knee extensor torques and extensor angular impulses from the two analyses were regressed onto BMI. Inverse dynamics are the standard analytical technique used to calculate joint torques during a variety of movements including locomotion. Inverse dynamics typically uses experimentally observed, subject-specific body kinematics and ground reaction forces but standardized body segment inertial parameters (BSIPs) that distribute masses to each segment based on a single set of relative weightings for all participants. Based on the observations that hip joint torques during the stance phase of walking are meaningfully affected by BSIP values (2), that obese vs. lean have altered mass distributions, and that faster walking speeds have larger segmental accelerations, we expect that joint torque predictions would be more accurate when based on subject- specific BSIPs particularly in obese individuals. We hypothesize that the magnitude of the differences between joint torques derived with standard vs. subject-specific BSIPs will be directly related to the magnitude of obesity and to walking speed.Methods Conclusion References All results showed significant, positive, curvilinear relationships between the differences in torques and angular impulses and BMI and the strength of the relationships increased with walking speed (table 1). The magnitude of the differences became substantially larger as BMI increased, particularly at values over 30 kg/m 2 at which point differences reached 10% of the maximum hip torque values. These data suggest the use of subject-specific BSIPs for obese individuals, derived through either measurement-based techniques or from population-based regression equations would be beneficial for predicting lower extremity joint torques during walking. Dual X-Ray Absorptiometry Table 1. Coefficients of determination from regression analysis between differences in joint torques predicted with standardized vs. subject-specific BSIPs and BMI at three walking speeds. Dual x-ray absorptiometry (DXA) is currently considered the most accurate method of measuring body composition. DXA is able to define bone mineral density, lean tissue mass, and adipose tissue mass using a lower does of radiation than the traditional MRI and greater accuracy than anthropometric measurements. Programmed settings typically calculate these values for trunk, arm, and leg segments. For this study, custom segments were defined using guidelines from Browning, et al (1). These segments allowed for the calculation of pelvis, thigh, shank, and foot masses. Customized Body Segment Parameters Standard Body Segment Parameters Comparison of %Body Mass between Standard Segment Masses and Custom Segment Masses Visual 3D Locomotion Videos Standard Segment Masses (from Dempster) Custom Segment Masses Visual 3D Locomotion Videos Hip Angular Impulse Knee Torque