Low Back Pain Suppresses Preparatory and Triggered Upper-Limb Activation After Sudden Upper-Limb Loading

Department of Neurosurgery, Kuopio University Hospital, Kuopio, Finland.
Spine (Impact Factor: 2.3). 04/2007; 32(5):E150-5. DOI: 10.1097/01.brs.0000256886.94791.94
Source: PubMed


A cross-sectional comparative study between healthy controls and patients with chronic low back pain (LBP).
To assess the effect of chronic LBP on biceps brachii muscle activation during sudden upper-limb loading.
Chronic LBP is related to altered trunk muscle function. However, it is not known if these changes are also found in upper-limb function, indicating a general effect.
Surface electromyographic recordings were made from the biceps brachii bilaterally from 22 control subjects without chronic LBP and 29 patients with chronic LBP. Electromyography was recorded during expected and unexpected limb loading, with the activation pattern recorded for analysis at 150 milliseconds before loading, and 3 consecutive 50 milliseconds periods following loading. RESULTS.: Chronic LBP patients had decreased biceps brachii activation before expected perturbation (P = 0.035) and during the third 50-millisecond period (from 100 to 150 milliseconds) after unexpected perturbation (P = 0.010). During the first 2, 50-millisecond periods (from 0 to 100 milliseconds) after the perturbation, the activation was similar.
Chronic LBP did not affect reflex activation of biceps brachii muscles but decreased preparatory and triggered reactions. The finding indicates that back pain may disturb higher level information processing in motor control.

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    • "This is functionally meaningful and allows reflexes to be integrated into complex movements initiated by supraspinal commands [6]. Moreover, in preparation for an upcoming movement task reflexes can adapt in advance to assist the performance of that task [7], [8]. Reflex gain can even change due to the mere observation of an action [9]–[11] and is modulated in the same manner during passive observation of walking and during active execution of the same action [12]. "
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    ABSTRACT: Seeing an action activates neurons in the premotor, motor, and somatosensory cortex. Since a significant fraction of these pyramidal neurons project to the spinal motor circuits, a central question is why we do not automatically perform the actions that we see. Indeed, seeing an action increases both cortical and spinal excitability of consistent motor patterns that correspond to the observed ones. Thus, it is believed that such imitative motor patterns are either suppressed or remain at a sub-threshold level. This would predict, however, that seeing someone make a corrective movement while one is actively involved in the same action should either suppress evoked responses or suppress or modulate the action itself. Here we tested this prediction, and found that seeing someone occasionally stepping over an obstacle while walking on a treadmill did not affect the normal walking pattern at all. However, cutaneously evoked reflexes in the anterior tibial and soleus muscles were modulated as if the subject was stepping over an obstacle. This result thus indicates that spinal activation was not suppressed and was neither at sub-threshold motor resonance. Rather, the spinal modulation from observed stepping reflects an adaptive mechanism for regulating predictive control mechanisms. We conclude that spinal excitability during action observation is not an adverse side-effect of action understanding but reflects adaptive and predictive motor control.
    Full-text · Article · Aug 2014 · PLoS ONE
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    • "As hypothesized, RT of CLBP patients differed significantly from that of healthy subjects in all three conditions. This is in agreement with studies that found delayed muscle reaction times in CLBP patients as a responds to sudden (trunk) loading [16,17]. However, only a few other studies addressed pain patients' performance on an explicit motor RT task comparable to the one in the present study. "
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    ABSTRACT: Chronic low back pain (CLBP) is often accompanied by an abnormal motor performance. However, it has not been clarified yet whether these deviations also occur during motor tasks not involving the back and whether the performance is influenced by pain and pain-related cognitions. Therefore, the aim of the present study is to get insight in the contribution of both pain experience and pain-related cognitions to general motor task performance in CLBP. 13 CLBP patients and 15 healthy subjects performed a hand-function task in three conditions: sitting, lying prone (lying) and lying prone without trunk support (provoking). The last condition was assumed to provoke pain-related cognitions, which was considered successful when a patients' pain expectancy on a numeric rating scale was at least 1 point higher than actual pain experienced. Subjects' performance was expressed in reaction time and movement time. Repeated measures analysis of variance was performed to detect main effect for group and condition. Special interest was given to group*condition interaction, since significant interaction would indicate that patients and healthy subjects performed differently throughout the three conditions. Patients were slower throughout all conditions compared to healthy subjects. With respect to the provoking condition, patients showed deteriorated performance compared to lying while healthy subjects' performance remained equal between these two conditions. Further analysis of patients' data showed that provocation was successful in 54% of the patients. Especially this group showed deteriorated performance in the provoking condition. It can be concluded that CLBP patients in general have worse motor task performance compared to healthy subjects and that provoking pain-related cognitions further worsened performance.
    Full-text · Article · Sep 2011 · BMC Musculoskeletal Disorders

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