title: Analysis of Difference in Center-of-Pressure Positions Between Experts and Novices During Asymmetric Lifting.
abstract: Although numerous studies have analyzed the relationship between manual material handling (MMH) and the forces acting on the lumbar spine, the difference in the MMH between experts and novices through the analysis of measured data has not been well studied. The purpose of this paper was to analyze the difference in the MMH positions between ten skilled experts working at a freight transport company (Group 1) and five unskilled novices without any experience (Group 2) during asymmetric lifting. All the human subjects performed asymmetric lifting experiments with closed eyes; the experiments involved moving loads (6 and 18 kg) to the left side. Time series data of the vertical ground reaction force were measured, using a Wii Balance Board, and then, the center-of-pressure (CoP) trajectories were calculated. The balance board was used for the measurement, because it was reliable, inexpensive, and portable and provided good repeatability even on rough surfaces, and all the information pertaining to the load and worker under various conditions was captured without any omissions. Under the 18 kg load condition, the CoP positions for Group 2 were located on the same side during left asymmetric lifting; however, those for Group 1 were located on the opposite side during left asymmetric lifting ([Formula: see text]). Furthermore, under the 6 kg load condition, the load weight influenced asymmetric lifting for most subjects of Group 2 such that the CoP positions were located on the opposite side ([Formula: see text]). Based on the simulation and electromyography measurement results, we inferred that the difference in the CoP positions between the two different groups could be attributed to the difference in the hip positions. Most skilled experts position their hips in such a way that their CoP trajectories move toward the opposite side during left asymmetric lifting. Although the skillful characteristics of experts may be responsible for the lightening of the burden on the waist during asymmetric lifting, there are still two points that this paper does not clarify: the relationship between the experts' adjustment of the hip position and the load of the weight, and the influence of an imbalance of the CoP position on the forces acting on the lumbar spine.
authors.affiliation: Department of Robotics & Design for Innovative Healthcare Graduate School of Medicine Osaka University Osaka 565-0871 Japan.
authors.forename: Hieyong
authors.initials: H
authors.lastname: Jeong
authors.affiliation: Department of Robotics & Design for Innovative Healthcare Graduate School of Medicine Osaka University Osaka 565-0871 Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamada
authors.affiliation: Division of Health Sciences, Graduate School of Medicine Osaka University Osaka 565-0871 Japan.
authors.forename: Michiko
authors.initials: M
authors.lastname: Kido
authors.affiliation: Department of Mechanical Engineering Graduate School of Engineering Kindai University Osaka 577-8502 Japan.
authors.forename: Shima
authors.initials: S
authors.lastname: Okada
authors.affiliation: Department of Mechanical Science and Bioengineering Graduate School of Engineering Science Osaka University Osaka 560-0043 Japan.
authors.forename: Taishin
authors.initials: T
authors.lastname: Nomura
authors.affiliation: Department of Robotics & Design for Innovative HealthcareGraduate School of MedicineOsaka UniversityOsaka565-0871Japan; Division of Health Sciences, Graduate School of MedicineOsaka UniversityOsaka565-0871Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ohno
keywords: Asymmetric lifting; center of pressure; foot pressure distribution; hip position; vertical ground reaction force