When is a lifting movement too asymmetric to identify low-back loading by 2-D analysis?
In ergonomics research, two-dimensional (2-D) biomechanical models are often used to study the mechanical loading of the low back in lifting movements. When lifting movements are asymmetric, errors of unknown size may be introduced in a 2-D analysis. In the current study, an estimation of these errors was made by comparing the outcome of a 2-D analysis to the results of a recently developed and validated 3-D model. Four subjects made two repetitions of five lifting movements, differing in the amount of asymmetry. The results showed a significant underestimation of the peak torque by 20, 36 and 61% when the initial position of a box was rotated 30, 60 and 90 degrees with respect to the sagittal plane of the subject. The main cause of this underestimation was a pelvic twist, resulting in an erroneous projection of a pelvic marker on to the sagittal plane due to pelvic twist. It is suggested that from 30 degrees box rotation a 2-D analysis may easily lead to wrong conclusions when it is used to study asymmetric lifting.
Kingma
I
I
Amsterdam Spine Unit, Faculty of Human Movement Sciences, Vrije Universiteit, The Netherlands.
de Looze
M P
MP
van Dieën
J H
JH
Toussaint
H M
HM
Adams
M A
MA
Baten
C T
CT
D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007403:Intervertebral Disc / Q000502:physiology; D017770:Lifting; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D009949:Orientation / Q000502:physiology; D011187:Posture / Q000502:physiology; D012447:Sacrum / Q000502:physiology*; D014741:Video Recording; D016474:Weight-Bearing / Q000502:physiology*