Objective: The purpose of this study was to investigate the clinical usefulness of the flexion relaxation response test (FRT) in subjects undergoing an episode of acute nonspecific low back pain (LBP). Specifically, it determined if the flexion relaxation ratio (FRR), derived from components of the FRT, can be an effective and reliable measure of therapeutic benefit to the intervention of spinal manipulation (SM). This study explored the relationship between the FRR, left and right paraspinal muscles individually, and the patient self-reported outcome measures of Numeric Pain Rating Scale (NPRS) and Oswestry Disability Index (ODI). Methods: Thirty consecutive subjects with LBP underwent repeated measures testing in an outpatient physical therapy clinical setting. Pre-intervention measures before sessions #1, 3, 6, 9, and 12 included NPRS, ODI, surface electromyography (EMG), as well as post-intervention EMG. A cycle of three repetitions was perfomed, repositioning slowly from standing erect to full trunk flexion, holding for 3 seconds, then extending back to the starting upright positiion. FRR was then determined. Each subject receieved tow interventions of SM per session, minimum of 3 to a maximim of 12 sessions within six weeks. Results: By analyzing FRR values through treatment, this study found a statistically significant increase in the FRR. Mean NPRS and ODI scores did decrease throughout treatment. We had hypothesized that clinicians would be able to reliably use the FRR as an objective measure in association with patient self-reported outcome measures in assessing the response to the treatment intervention of SM during an episode of acute LBP. However, this study did not find a statistically significant correlation between the FRR and patient outcome measures. Clinical Relevance/Conclusion: This study of acute LBP subjects found that the increase in FRR was responsive to multiple SM interventions, inferring benefit. Despite this finding, there was no significant correlation found between the FRR and patient-reported outcome measures. These conclusions encourage further investigation into the use of EMG as an objective measure in assessing LBP response to SM intervention.
