Assessing the Sensitivity of the Ratio Method in Identifying the Flexion-Relaxation Phenomenon in People With Non-specific Low Back Pain and Healthy People

Background and Aims There are different methods for quantifying the flexion-relaxation phenomenon (FRP). However, there is little standardization for them. This study aimes to evaluate the sensitivity of the ratio method in identifying the FRP in people with non-specific low back pain (LBP) and healthy people.Methods In this study,10 patients with nonspecific LBP and 10 healthy people participated voluntarily. They performed a trunk flexion with a straight knee. Each trunk flexion was done in four modes: (1) standing in the starting position, (2) trunk flexion at a fixed speed (using a metronome), (3) full flexion, and (4) trunk extension to the standing position. Each mode took 5 seconds and was performed 3 times. Then, the FRP was investigated using the ratio method as well as the visual inspection method.Results The sensitivity of all ratios in identifying the FRP in healthy people was 100%, except for the third ratio (the root mean square of EMG activity in a standing position divided by the root mean square in flexion mode), which was 60%. In the LBP group, the sensitivity of the first ratio was 70%; for the second ratio, it was 80%; for the third ratio, 40%; for the fourth ratio, 50%; for the fifth mode (the root mean square in extension mode divided by the root mean square in full flexion mode), 40%; and for the sixth mode, 50%.Conclusion All ratios (except for the second ratio) are valid for identifying the FRP in healthy people, but caution should be taken in using the ratio method for people with LBP; only the second ratio (maximum EMG activity in the extension mode divided by the average EMG activity in the full flexion mode) should be used for these individuals.