Active Trunk Stiffness Increases with Co-contraction.
From: Musculoskeletal Biomechanics Laboratories, Department of Engineering Science and Mechanics, School of Biomedical Engineering and Science, Virginia Polytechnic Institute and State University, 219 Norris Hall, 0219, Blacksburg, VA 24061, USA.
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology
- Publish Date: Feb 2006
- ISSN: 1050-6411
- Volume: 16
- Issue: 1
- Pages: 51-7
- Medium: Print
- Language: English
- Citation (JAMA): Lee Patrick J, Rogers Ellen L, Granata Kevin P, et al. Active Trunk Stiffness Increases with Co-contraction.. Feb 2006;16:51-7
Abstract
Trunk dynamics, including stiffness, mass and damping were quantified during trunk extension exertions with and without voluntary recruitment of antagonistic co-contraction. The objective of this study was to empirically evaluate the influence of co-activation on trunk stiffness. Muscle activity associated with voluntary co-contraction has been shown to increase joint stiffness in the ankle and elbow. Although biomechanical models assume co-active recruitment causes increase trunk stiffness it has never been empirically demonstrated. Small trunk displacements invoked by pseudorandom force disturbances during trunk extension exertions were recorded from 17 subjects at two co-contraction conditions (minimal and maximal voluntary co-contraction recruitment). EMG data were recorded from eight trunk muscles as a baseline measure of co-activation. Increased EMG activity confirms that muscle recruitment patterns were different between the two co-contraction conditions. Trunk stiffness was determined from analyses of impulse response functions (IRFs) of trunk dynamics wherein the kinematics were represented as a second-order behavior. Trunk stiffness increased 37.8% (p < 0.004) from minimal to maximal co-activation. Results support the assumption used in published models of spine biomechanics that recruitment of trunk muscle co-contraction increases trunk stiffness thereby supporting conclusions from those models that co-contraction may contribute to spinal stability.
Mesh Headings (Keywords): Back, Biomechanics, Electromyography, Humans, Muscle Contraction, Muscle, Skeletal, Rectus Abdominis, Spine
Check for Full Text / PubMed Unique Identifier (PMID): 16099678
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