The influence of fatigue and chronic low back pain on muscle recruitment patterns following an unexpected external perturbation

Júlia Jubany,Rosa Angulo-Barroso,Lieven Danneels

doi:10.1186/s12891-017-1523-3

Abstract

BackgroundChronic low back pain (CLBP) has been associated with altered trunk muscle responses as well as increased muscle fatigability. CLBP patients and fatigued healthy subjects could experience similar neuromuscular strategies to attempt to protect the spine. The current study examined muscle activation differences between healthy and CLBP subjects following a perturbation. In addition, the possible role of muscle fatigue was evaluated by investigating the healthy control subjects in a non-fatigued and a fatigued condition. Both experiments were combined to evaluate possible similar strategies between CLBP and fatigued samples.MethodsCross-sectional study where 24 CLBP subjects and 26 healthy subjects were evaluated. Both groups (CLBP vs. healthy) and both conditions (non-fatigued and a fatigued condition) were evaluated while a weight was suddenly dropped on a held tray. Erector spinae, multifidus, obliques and biceps brachii were recorded using surface electromyography. Variables describing the bursts timing and variables describing the amount of muscle activity (number of bursts and amplitude increase) post impact were studied. The analysis between groups and conditions was carried out using ANOVAs with repeated measurements for the muscle factor.ResultsCLBP subjects reacted similarly to healthy subjects regarding muscle activity post impact. However, the CLBP group showed temporal characteristics of muscle activity that were in between the fatigued and non-fatigued healthy group. Clear differences in muscle activity were displayed for healthy subjects. Fatigued healthy subjects presented more reduced activity after impact (upper limb and trunk muscles) than non-fatigued healthy subjects and different temporal characteristic in the same way than CLBP patients. This same temporal characteristic with CLBP and healthy fatigued people was a delay of the first burst of muscle activity after impact.ConclusionThough similar muscle pattern existed between CLBP and healthy people, CLBP temporal characteristics of muscle activity showed a pattern in between healthy people and fatigued healthy people. While the temporal muscle pattern dysfunction used by CLBP subjects could be related to maladaptive patterns, temporal and muscle activity characteristics used by healthy fatigued people may lead to back injuries.

Highlights

Chronic low back pain (CLBP) has been associated with altered trunk muscle responses as well as increased muscle fatigability
When fatigued healthy individuals were exposed to a sudden perturbation, some studies demonstrated increases in the electromyographic (EMG) amplitude as a strategy to compensate for the loss of force production [8]; others demonstrated lower trunk muscle cocontraction compared to non-fatigued people, which was associated to spinal stability vulnerability [9]; and others found longer activation latencies as a deterioration of responsiveness and precision of the neuromuscular spindle system [10]
The The healthy group after the fatigue protocol (With-F) condition showed a significantly shorter length of the biceps brachii (BB) first burst when compared to the The healthy group without fatigue (Non-F) condition (Table 4 and Fig. 3)

Summary

Introduction

Chronic low back pain (CLBP) has been associated with altered trunk muscle responses as well as increased muscle fatigability. Trunk neuromuscular deficiency has been associated with low back pain: delays in activation (larger muscle activation latencies) [2, 3] and higher levels of muscle activation and trunk muscle cocontraction [3, 4]. These deficits have been related as a goal to protect from further pain, injury, or both, but in the same way as a possible source of further problems in the long term and have been suggested to contribute to CLBP [5]. When fatigued healthy individuals were exposed to a sudden perturbation, some studies demonstrated increases in the electromyographic (EMG) amplitude as a strategy to compensate for the loss of force production [8]; others demonstrated lower trunk muscle cocontraction compared to non-fatigued people, which was associated to spinal stability vulnerability [9]; and others found longer activation latencies as a deterioration of responsiveness and precision of the neuromuscular spindle system [10]

Methods

Results

Discussion

Conclusion