Abstract
The purpose of this study was to investigate the contribution of individual muscles (MJRSm) to total joint rotational stiffness (MJRST) about the lumbar spine's L4-5 joint prior to, and following, sudden dynamic flexion or extension perturbations to the trunk. We collected kinematic and surface electromyography (sEMG) data while subjects maintained a kneeling posture on a parallel robotic platform, with their pelvis constrained by a harness. The parallel robotic platform caused sudden inertial trunk flexion or extension perturbations, with and without the subjects being aware of the timing and direction. Prevoluntary muscle forces incorporating both short and medium latency neuromuscular responses contributed significantly to joint rotational stiffness, following both sudden trunk flexion and extension motions. MJRST did not change with perturbation direction awareness. The lumbar erector spinae were always the greatest contributor to MJRST. This indicates that the neuromuscular feedback system significantly contributed to MJRST, and this behaviour likely enhances joint stability following sudden trunk flexion and extension perturbations.
Highlights
Ere is a complex arrangement of bones, ligaments, muscle, and nervous tissue which combine to maintain the structural integrity of the spine, reducing the potential for system buckling
During the forced extension conditions, we expected that the internal oblique (IO) and external oblique (EO) muscles would be the main contributors to MJRST, since they acted as antagonists during the motion
The magnitudes of the prevoluntary muscle forces are smaller than those produced voluntarily, our data suggests that subjects adopted a response strategy that relies on prevoluntary muscle forces to produce rapid increases in joint rotational stiffness following a perturbation
Summary
Ere is a complex arrangement of bones, ligaments, muscle, and nervous tissue which combine to maintain the structural integrity of the spine, reducing the potential for system buckling. Speci c to the lumbar spine, to limit such interactions the sudden perturbations should cause joint motion about the exion/extension axis given that rotation about this axis presents less of a challenge to the neuromuscular system based on the symmetrical design of the bilateral exor and extensor musculature. E purpose of this research was to investigate the contribution of the trunk muscles to joint rotational stiffness about the lumbar spine’s L4-5 joint prior to, and following, sudden dynamic exion and extension perturbations to the trunk. This project examined the sum of all muscles contributing to the total MJRS (MJRST), as well as the contribution of individual muscles to MJRST (MJRSm). It was hypothesized that prior knowledge of the perturbation direction would cause a neuromuscular strategy such that individual muscle contributions to MJRST would be dependent upon the forced direction
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