Abstract
Postural reflexes are essential for locomotion and postural stability, and may play an important role in the etiology of chronic back pain. It has recently been theoretically predicted, and with the help of unilateral perturbations of the trunk experimentally confirmed that the sensorimotor control must lower the reflex amplitude for increasing reflex delays to maintain spinal stability. The underlying neuromuscular mechanism for the compensation of postural perturbations, however, is not yet fully understood. In this study, we applied unilateral and bilateral sudden external perturbations to the trunk of healthy subjects and measured the muscular activity and the movement onset of the trunk. We found that the onset of the trunk muscle activity is prior to, or coincident with, the onset of the trunk movement. Additionally, the results of our experiments imply that the muscular response mechanism integrates distant sensory information from both sides of the body. These findings rule out a simple monosynaptic stretch reflex in favor of a more complex polysynaptic postural reflex mechanism to compensate postural perturbations. Moreover, the previously predicted negative correlation between reflex delay and reflex gain was also confirmed for bilateral perturbations.
Highlights
People suffering from chronic low back pain (CLBP) exhibit delayed postural reflexes (Magnusson et al, 1996; Hodges and Richardson, 1998; Radebold et al, 2000, 2001; Leinonen et al, 2001; Reeves et al, 2005; Abboud et al, 2017) which are supposed to have an influence on the stability of the human spine
The ipsilateral reflex delays were significantly longer than the contralateral ones
Bonferroni-adjusted post-hoc comparisons (α = 0.05/4; p < 0.0125) revealed that the onset of the surface electromyography (sEMG) response of the contralateral erector spinae pars lumborum (ES) muscles occurred ∼20–30 ms earlier than the kinematic response onset of the L1-marker, which resulted in a significant difference for the ES1 (p < 0.01) and an almost significant difference for the ES2 (p = 0.021)
Summary
People suffering from chronic low back pain (CLBP) exhibit delayed postural reflexes (Magnusson et al, 1996; Hodges and Richardson, 1998; Radebold et al, 2000, 2001; Leinonen et al, 2001; Reeves et al, 2005; Abboud et al, 2017) which are supposed to have an influence on the stability of the human spine. Franklin and Granata (2007) and Liebetrau et al (2013) performed model-based spine stability analyses and found a negative correlation between reflex delay and reflex amplitude. They predicted that a delayed muscular response requires its amplitude to be decreased in order to not destabilize the spine. This model prediction has been experimentally confirmed by applying sudden unilateral perturbations to the trunk (Liebetrau et al, 2013). Lateral perturbations induce a specific reaction pattern of the postural regulation where the contralateral trunk muscle response is significantly
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