Effects of low back pain stabilization or movement system impairment treatments on voluntary postural adjustments: a randomized controlled trial

Abstract

Background: People with low back pain (LBP) exhibit impaired anticipatory postural adjustments (APAs).

Objective: To evaluate whether current motor retraining treatments address LBP-associated changes in movement coordination during tasks that do and do not require APAs.

Design: Prospectively registered randomized controlled trial with a blinded assessor.

Setting: Outcome evaluations occurred in a university laboratory; treatments were carried out in outpatient physical therapy clinics.

Patients: Fifteen subjects without LBP and 33 subjects with chronic, recurrent, and nonspecific LBP.

Intervention: Twelve subjects with LBP received stabilization treatment, 21 received movement system impairment-based treatment, for more than 6 weekly 1-hour sessions plus home exercises.

Measurements: Pre- and post-treatment, surface electromyography (EMG) was recorded bilaterally from trunk and leg muscles during unsupported and supported leg-lifting tasks, which did and did not require an APA, respectively. Vertical reaction forces under the contralateral leg were recorded to characterize the APA. Oswestry disability scores and numeric pain ratings were also recorded.

Results: Persons with LBP demonstrated an impaired APA compared with persons without LBP, characterized by increased premovement contralateral force application and increased postmovement trunk EMG amplitude, regardless of the task. After treatments, both groups similarly improved in disability and function; however, APA characteristics did not change (ie, force application or EMG amplitude) in either task.

Limitations: Treating clinicians were not blinded to treatment allocation, only short-term outcomes were assessed, and main effects of treatment do not rule out nonspecific effects of time or repeated exposure.

Conclusions: Movement impairments in persons with LBP are not limited to tasks requiring an APA. Stabilization and movement system impairment-based treatments for LBP do not ameliorate and may exacerbate APA impairments (ie, excessive force application and increased post-movement trunk muscle activation).

Keywords: Aberrant movement patterns; Anticipatory postural adjustment (APA); Force application.; Low back pain (LBP); Movement systems impairment (MSI) approach; Stabilization approach.

Figure 1

Experimental tasks and variables. A) Supported leg raise task (SLR); B) Unsupported leg raise task (ULR), and; C) Schematic of the vertical ground reaction forces under the feet (Fz) as well as representative EMG from a subject without LBP. The graphs of representative EMG illustrate the task dependence and temporal characteristics of EMG burst activity for muscles of the leg: from top to bottom, the left long-head of biceps femoris (BFM), the left rectus femoris (RFM), the right BFM, and the right RFM. Black traces represent responses during the ULR task; gray traces represent responses during the SLR task. Time 0 represents movement onset. The dashed black vertical line indicates the movement onset.

Figure 2

Flow of subjects through APA substudy.

Figure 3

Summary of vertical reaction force data from the contralateral limb. A) Percentage of trials where movement onset occurred during supported (SLR and unsupported (ULR) leg raises; B) Mean vertical reaction force amplitude during SLR and ULR, and; C) Time to vertical reaction force loading relative to movement onset. In the left panel, white bars represent the control group, while black represent the age-, sex-matched subgroup of persons with LBP prior to receiving treatment. In the right panel, grey and striped bars represent pre- and post-treatment values, respectively for the STB or MSI groups as indicated.

Figure 4

Summary of mean normalized integrated surface EMG during the PRE phase for: A) the unsupported (ULR) and B) the supported (SLR leg raising tasks. In the left panel, white bars represent the control group, while black represent the age-, sex-matched subgroup of persons with LBP prior to receiving treatment. In the right panel, grey and striped bars represent change in EMG amplitude the STB or MSI groups, respectively.