Evaluation of flexion-relaxation in the thoracic erector spinae and superficial lumbar multifidus during standing flexion and slumped sitting

Abstract

INTRODUCTION: Low back pain is a highly prevalent and costly condition which is often difficult to diagnose. Evaluation of the flexion-relaxation response has been used to objectively assess the neuromuscular adaptation associated with low back pain, and has attracted much clinical interest due its impressive ability to distinguish between low back pain patients and pain-free controls. Numerous methods have been used to quantify flexion-relaxation, yet it remains uncertain which method is most appropriate to quantify the response. Furthermore, flexion-relaxation has been evaluated at different muscle sites and during different flexion tasks; however, the influence of muscle site and flexion task on flexion-relaxation remains unclear.

AIM: The aim of the present study was to i) compare different methods of analysis used to evaluate flexion-relaxation (FR) including dichotomous criteria and quantitative methods; and ii) to investigate the influence of surface electrode site (thoracic and lumbar), and flexion task (standing flexion and slumped sitting) in pain-free participants.

DESIGN: A normative, single-group observational study was conducted.

PARTICIPANTS: 20 healthy, pain-free volunteers (n=12 males, 8 females; mean age±SD = 27.9±7.7y), were recruited from a university population.

METHODS: Surface electromyography was used to measure activity in the thoracic erector spinae (TES) and superficial lumbar multifidus (SLM) bilaterally while participants performed standing flexion and slumped sitting tasks. The presence of FR was determined by using six criteria previously defined in the literature and a comparison of these criteria was undertaken. Flexion-relaxation ratios (FRR) and extension-relaxation ratios (ERR) were also calculated for each of the conditions.

RESULTS: There was a large variation in the presence of FR based on the criteria examined. Depending on which criterion was applied, between 7.5% (3/40) and 95% (38/40) of TES sites; and between 27.5% (11/40) and 100% (40/40) of SLM sites were considered to have reached FR during standing flexion. During slumped sitting, between 35% (15/40) and 95% (38/40) of TES sites; and between 17.5% (7/40) and 75% (30/40) of SLM sites were considered to have reached FR. The majority of criteria identified FR more frequently in the TES during slumped sitting compared with standing flexion, and more frequently in the SLM during standing flexion compared with slumped sitting. The ERR was significantly greater (p< 0.001) than the FRR in the SLM during standing flexion. The FRR and ERR were both significantly greater (p < 0.001) in the SLM during standing flexion compared with slumped sitting.

CONCLUSION The findings of this study indicate that there is substantial variation in determining the presence of FR dependent on the criteria examined when evaluating the TES and SLM during standing flexion and slumped sitting. The flexion task performed can facilitate or hinder FR depending on the muscle being evaluated. There is a need for consensus within the research community as to which method is most appropriate to evaluate FR. The findings suggest that quantitative methods which measure the extent of FR may be more suitable to evaluate the response.