Flexion Relaxation Ratio Not Responsive to Acutely Induced Low Back Pain from a Delayed Onset Muscle Soreness Protocol.

Maggie E Horn,Mark D Bishop

doi:10.1155/2013/617698

Abstract

Background. The flexion relaxation ratio (FRR) has been suggested as a measure of muscular performance in patients with low back pain (LBP). The purpose of this study was to investigate whether the FRR was responsive to acute LBP produced from a delayed onset muscle soreness (DOMS) protocol. Methods. Fifty-one pain-free volunteers performed DOMS to induce LBP. Current pain intensity, trunk flexion range of motion (ROM), and passive straight leg raise (SLR) were measured at baseline, 24 and 48 hours after DOMS. Participants were categorized into pain groups based on reported current pain intensity. Changes in FRR, trunk flexion ROM, and SLR ROM were examined using two-way repeated measures analysis of variance. Results. Pain group was not found to have a significant effect on FRR (F 1,29 = 0.054, P = 0.818), nor were there any two-way interactions for changes in FRR. The pain group had decreased trunk flexion ROM compared to the minimal pain group (F 1,38 = 7.21, P = 0.011), but no decreases in SLR ROM (F 1,38 = 3.51, P = 0.057) over time. Interpretation. There were no differences in FRR based on reported pain intensity of LBP from a DOMS protocol. The responsiveness of FRR might be limited in patients with acute onset LBP of muscular origin.

Highlights

During normal trunk flexion in standing the trunk extensor muscles act eccentrically and are considered myoelectrically “active” until a distinct point in the trunk flexion range of motion (ROM) where the lumbar paraspinals relax
Groups did not differ at baseline in age, gender, straight leg raise (SLR), or flexion relaxation ratio (FRR) but differed in trunk ROM (t = 2.24, P = 0.031), where the pain group had slightly decreased trunk ROM compared to the minimal pain group
Correlations revealed a negative correlation between age and sex (r = −0.32, P = 0.04), a negative correlation between change in pain and change in trunk flexion ROM (r = −0.375, P = 0.014), and a positive correlation between change in SLR and FRR at 48 hours (r = 0.494, P = 0.003)

Summary

Introduction

During normal trunk flexion in standing the trunk extensor muscles act eccentrically and are considered myoelectrically “active” until a distinct point in the trunk flexion range of motion (ROM) where the lumbar paraspinals relax. Passive structures and pelvic musculature provide the functional limit to terminal flexion ROM During this time of “relaxation,” the paraspinal muscles of the trunk are considered myoelectrically “quiet” or electrically reduced. Neblett et al (2003) followed patients with chronic LBP over a seven-week rehabilitation program These investigators reported that 10 of 47 (21.3%) patients with LBP showed normal flexion relaxation prior to treatment. The flexion relaxation ratio (FRR) has been suggested as a measure of muscular performance in patients with low back pain (LBP). Trunk flexion range of motion (ROM), and passive straight leg raise (SLR) were measured at baseline, 24 and 48 hours after DOMS. The responsiveness of FRR might be limited in patients with acute onset LBP of muscular origin

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