Article

Electromyography-assisted (EMG-assisted) biomechanical models are
used to characterize the muscle and joint reaction forces in the lumbar region.
However, during a full-range trunk flexion, there is a transition of extension
moment from the trunk extensor muscles to the passive tissues of the low back,
indicating that the empirical EMG data used to drive these EMG-assisted models
becomes less correlated with the extensor moment. The objectives of this study
were to establish the trunk flexion angles at which the passive tissues generate
substantial trunk extension moment and to document how these angles change with
asymmetry. METHODS: Participants performed controlled trunk flexion-extension
motions in three asymmetric postures. The trunk kinematics data and the
electromyographic activity from L3- and L4-level paraspinals and rectus abdominis
were captured. The time-dependent net internal active moment (from an
EMG-assisted model) and the net external moment were calculated. The trunk and
lumbar angles at which the net internal active moment was less than 70% of the
external moment were found. FINDINGS: The trunk flexion angle at which the net
internal moment reaches the stated criteria varied as a function of asymmetry of
trunk flexion motion with the sagittally symmetric case providing the deepest
flexion angle of 38 degrees (asymmetry 15 degrees : 33 degrees ; asymmetry 30
degrees : 26 degrees ). INTERPRETATION: These results indicate that EMG-assisted
biomechanical models need to consider the role of passive tissues at trunk
flexion angles significantly less than previously thought and these flexion
angles vary as a function of the asymmetry and direction of motion.
CI - Copyright (c) 2011 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS