title: A nonlinear dynamics of trunk kinematics during manual lifting tasks.
abstract: 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.
authors.affiliation: Industrial Engineering Department, College of Engineering, King Saud University, Riyadh, Saudi Arabia.|Department of Mechanical Engineering, College of Engineering, Al-Azhar University, Nasr City, Cairo, Egypt.
authors.forename: Tamer
authors.initials: T
authors.lastname: Khalaf
authors.affiliation: Department of Industrial Engineering and Management Systems, University of Central Florida, Orlando, FL, USA.
authors.forename: Waldemar
authors.initials: W
authors.lastname: Karwowski
authors.affiliation: Department of Industrial Engineering and Management Systems, University of Central Florida, Orlando, FL, USA.
authors.forename: Nabin
authors.initials: N
authors.lastname: Sapkota
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D017770:Lifting; D008297:Male; D017711:Nonlinear Dynamics; D060726:Torso / Q000502:physiology*; D055815:Young Adult
keywords: Manual lifting; deterministic chaos; low back; trunk kinematics