title: The changes of lumbar muscle flexion-relaxation phenomenon due to antero-posteriorly slanted ground surfaces.
abstract: Uneven ground surface is a common occupational injury risk factor in industries such as agriculture, fishing, transportation and construction. Studies have shown that antero-posteriorly slanted ground surfaces could reduce spinal stability and increase the risk of falling. In this study, the influence of antero-posteriorly slanted ground surfaces on lumbar flexion-relaxation responses was investigated. Fourteen healthy participants performed sagittally symmetric and asymmetric trunk bending motions on one flat and two antero-posteriorly slanted surfaces (-15° (uphill facing) and 15° (downhill facing)), while lumbar muscle electromyography and trunk kinematics were recorded. Results showed that standing on a downhill facing slanted surface delays the onset of lumbar muscle flexion-relaxation phenomenon (FRP), while standing on an uphill facing ground causes lumbar muscle FRP to occur earlier. In addition, compared to symmetric bending, when performing asymmetric bending, FRP occurred earlier on the contralateral side of lumbar muscles and significantly smaller maximum lumbar flexion and trunk inclination angles were observed. Practitioner Summary: Uneven ground surface is a common risk factor among a number of industries. In this study, we investigated the influence of antero-posteriorly slanted ground surface on trunk biomechanics during trunk bending. Results showed the slanted surface alters the lumbar tissue load-sharing mechanism in both sagittally symmetric and asymmetric bending.
authors.affiliation: a The Ergonomics Lab, Department of Industrial and Management Systems Engineering , West Virginia University , Morgantown , WV , USA.
authors.forename: Boyi
authors.initials: B
authors.lastname: Hu
authors.affiliation: a The Ergonomics Lab, Department of Industrial and Management Systems Engineering , West Virginia University , Morgantown , WV , USA.
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Ning
authors.affiliation: b Department of Civil and Environmental Engineering , West Virginia University , Morgantown , WV , USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Dai
authors.affiliation: a The Ergonomics Lab, Department of Industrial and Management Systems Engineering , West Virginia University , Morgantown , WV , USA.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Almuhaidib
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D006801:Humans; D007221:Industry / Q000379:methods; D017116:Low Back Pain / Q000517:prevention & control*; D008161:Lumbosacral Region / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009784:Occupational Diseases / Q000517:prevention & control*; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis / Q000517:prevention & control; D011187:Posture / Q000502:physiology; D018570:Risk Assessment; D060726:Torso / Q000502:physiology*
keywords: Uneven ground surface; flexion-relaxation phenomenon; lower back pain; trunk bending