Comparison Of Body Segment Moments Of Inertia In Male And Female Postmortem Human Specimens

Biomechanical models often rely on moments of inertia (MOIs) from male-only postmortem human specimens (PMHS). PURPOSE: To identify if body segment MOIs of male and female PMHS differed. METHODS: 27 PMHS, 12 male (M), 71.3 ± 16.4 years, 1.7 ± 0.1 m, 82.1 ± 12.4 kg, & 15 female (F) 70.8 ± 11.6 years, 1.6 ± 0.1 m, 66.3 ± 11.6 kg were segmented into 15 segments: head, torso, pelvis & right / left upper arm, forearm, hand, thigh, shank & foot. An inverted torsional pendulum technique was used to identify MOIs & those were converted to segmental MOIs utilizing anatomical axes: X-anterior, parallel to ground (long axis of feet); Y-left; & Z-vertical (feet/hands) or long bone axes. Data were analyzed using seven linear models: (1) no adjustment (2) normalized to total body mass (3) normalized to stature (4) normalized to both total body mass & stature (5) total body mass as covariate (6) stature as covariate (7) total body mass & stature as covariates. The best fit linear model was used to identify differences between sexes, α = 0.05. RESULTS: For 133/135 MOIs, the best fit linear model was the one normalized to both stature & total body mass. MOIs significantly differed by sex for 30/135 values. There were no differences for head, thorax, pelvis or right shank. MOIxx, MOIyy & MOIzz differed by sex for both hands (smallest difference, right hand MOIxx = F: 1.61E-4 ± 5.36E-5 kg*m, M: 3.49E-4 ± 1.58E-4 kg*m, p < 0.01) & feet (largest difference, left foot MOIyy = F: 0.0018 ± 0.0004 kg*m, M: 0.0034 ± 0.0008 kg*m, p < 0.01). For MOIxx, both upper arms, right forearm, left thigh & shank differed by sex. For MOIyy, left upper arm (F: 0.006 ± 0.006 kg*m, M: 0.018 ± 0.005 kg*m, p < 0.01), left thigh (F: -0.071 ± 0.027 kg*m, M: -0.045 ± 0.092 kg*m, p = 0.02) & left shank (F: 0.026 ± 0.006 kg*m, M: 0.028 ± 0.012 kg*m, p = 0.02) differed by sex. For MOIzz, both thighs differed by sex. For MOIzx, right upper arm, both forearms, & left thigh differed by sex. Other MOIs differences were MOIxz-left foot, MOIyx-right thigh; MOIyz-left upper arm. CONCLUSION: In a cohort of male & female PMHS, after normalization to body size parameters, 30 of 135 measured segmental MOIs significantly differed based on sex. In future biomechanical models, especially those for extremely dynamic activities, use of sex specific body segment parameters should be considered to obtain more accurate estimates of mechanics. US Army