BACKGROUND: Human responses at work may exhibit nonlinear
properties where small changes in the initial task conditions can lead to
large changes in system behavior. Therefore, it is important to study such
nonlinearity to gain a better understanding of human performance under a
variety of physical, perceptual, and cognitive tasks conditions.
OBJECTIVE: The main objective of this study was to investigate
whether the human trunk kinematics data during a manual lifting task
exhibits nonlinear behavior in terms of determinist chaos.
METHODS: Data related to kinematics of the trunk with respect to
the pelvis were collected using Industrial Lumbar Motion Monitor (ILMM), and
analyzed applying the nonlinear dynamical systems methodology. Nonlinear
dynamics quantifiers of Lyapunov exponents and Kaplan-Yorke dimensions were
calculated and analyzed under different task conditions.
RESULTS: The study showed that human trunk kinematics during
manual lifting exhibits chaotic behavior in terms of trunk sagittal angular
displacement, velocity and acceleration.
CONCLUSIONS: The findings support the importance of accounting for
nonlinear dynamical properties of biomechanical responses to lifting tasks.
