Altered postural responses persist following physical therapy of general versus specific trunk exercises in people with low back pain

Abstract

Interventions that target trunk muscle impairments in people with LBP have been promoted; however, the treatment effects on muscle activation impairments during postural tasks remain unclear. Thus, our objective was to evaluate the effects trunk stabilization vs. general strength and conditioning exercises on the automatic postural response in persons with chronic low back pain (LBP). Fifty-eight subjects with chronic, recurrent LBP (n = 58) (i.e., longer than six months) were recruited and randomly assigned to one of two, 10-week physical therapy programs: stabilization (n = 29) or strength and conditioning (n = 29). Pain and function were measured at 11 weeks and 6 months post-treatment initiation. To quantify postural following support surface perturbations, surface electrodes recorded electromyography (EMG) of trunk and leg muscles and force plates recorded forces under the feet, to calculate the center of pressure. Both groups demonstrated significant improvements in pain and function out to 6 months. There were also changes in muscle activation patterns immediately post-treatment, but not at 6 months. However, changes in center of pressure (COP) responses were treatment specific. Following treatment, the stabilization group demonstrated later onset of COP displacement, while the onset of COP displacement in the strengthening group was significantly earlier following treatment. Despite two different treatments, clinical improvements and muscle activation patterns were similar for both groups, indicating that the stabilization treatment protocol does not preferentially improve treatment outcomes or inter-muscle postural coordination patterns for persons with LBP.

Clinical trial registration number: NCT01611792.

Keywords: Electromyography; Low back pain (LBP); Physical therapy; Posture.

FIGURE 1

Flow of subjects through recruitment, randomization and stage at which subjects were lost to follow-up for the STB group (*5 unable to schedule 10 consecutive appointments, 1 workers compensation claim, and 1 injured knee sustained outside of treatment) and STC group (**5 unable to schedule 10 consecutive appointments, and 1 broken collarbone sustained outside of treatment).

FIGURE 2

Perturbation Directions and representative data. A) Schematic showing the 6 directions of translations with their induced sway direction, and; B) Representative platform displacement (upper) and net medio-lateral COP displacement (lower) for the STB (grey line) and STC (black line) during the baseline (grey dashed line box) and automatic (solid grey line) box), phases.

FIGURE 3

Pre-/post-treatment changes in mean, normalized, integrated EMG activity from week 0 to week 11 and month 6. Results are presented for (A) baseline and (B) automatic phases. Increases from week 0 to week 11 are denoted with black fill and decreases are denoted with grey fill. Changes that continue from week 11 to month 6 are denoted by “#” signs. Increases from week 0 to month 6 are denoted with black outline and decreases are denoted with grey outline. Grey dotted circles represent no significant group-by-visit effects for that muscle. See Table 3 for further information.

FIGURE 4

Mean center of pressure onset latency (ms) (A) and peak normalized center of pressure displacement (arbitrary units) (B) for the STB (upper) and STC (lower) groups during the pre-treatment and 11-weeks and 6-months post-treatment visits. In (A) grey diamonds reflect means individual subjects, black squares indicate overall group means, and asterisks indicate significant group-by-visit effects. In (B), dark grey filled boxed indicates pre-treatment, while dashed light grey and white boxes indicate post-treatment (11 weeks and 6 months, respectively) displacements for each group.