title: Effects of sex, age, body height and body weight on spinal loads: Sensitivity analyses in a subject-specific trunk musculoskeletal model.
abstract: Subject-specific parameters influence spinal loads and the risk of back disorders but their relative effects are not well understood. The objective of this study is to investigate the effects of changes in age (35-60 years), sex (male, female), body height (BH: 150-190cm) and body weight (BW: 50-120kg) on spinal loads in a full-factorial simulation using a personalized (spine kinematics, geometry, musculature and passive properties) kinematics driven musculoskeletal trunk finite element model. Segmental weight distribution (magnitude and location along the trunk) was estimated by a novel technique to accurately represent obesity. Five symmetric sagittal loading conditions were considered, and main effect plots and analyses of variance were employed to identify influential parameters. In all 5 tasks simulated, BW (98.9% in compression and 96.1% in shear) had the greatest effect on spinal loads at the L4-L5 and L5-S1 levels followed by sex (0.7% in compression and 2.1% in shear), BH (0.4% in compression and 1.5% in shear) and finally age (<5.4%). At identical BH and BW, spinal loads in females were slightly greater than those in males by ~4.7% in compression and ~8.7% in shear. In tasks with no loads in hands, BW-normalized spinal loads further increased with BW highlighting the exponential increase in spinal loads with BW that indicates the greater risk of back disorders especially in obese individuals. Uneven distribution of weight in obese subjects, with more BW placed at the lower trunk, further (though slightly <7.5%) increased spinal loads.
authors.affiliation: Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique, Montréal, Quebec, Canada.
authors.forename: F
authors.initials: F
authors.lastname: Ghezelbash
authors.affiliation: Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique, Montréal, Quebec, Canada. Electronic address: aboulfazl.shirazi@polymtl.ca.
authors.forename: A
authors.initials: A
authors.lastname: Shirazi-Adl
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran.
authors.forename: N
authors.initials: N
authors.lastname: Arjmand
authors.affiliation: Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique, Montréal, Quebec, Canada; Institut de recherche Robert Sauvé en santé et en sécurité du travail, Montréal, Canada.
authors.forename: Z
authors.initials: Z
authors.lastname: El-Ouaaid
authors.affiliation: Institut de recherche Robert Sauvé en santé et en sécurité du travail, Montréal, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Plamondon
authors.affiliation: Biophysics, University of Exeter, Exeter, UK.
authors.forename: J R
authors.initials: JR
authors.lastname: Meakin
mesh_terms: D000009:Abdominal Muscles / Q000503:physiopathology*; D000328:Adult; D000375:Aging; D001696:Biomechanical Phenomena; D001827:Body Height; D001835:Body Weight; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D008962:Models, Theoretical; D009765:Obesity / Q000503:physiopathology; D011187:Posture; D012680:Sensitivity and Specificity; D012727:Sex Characteristics; D016474:Weight-Bearing
keywords: Age; Body height; Finite element; Obesity; Sex; Trunk biomechanical modeling