Background: The flexion-relaxation phenomenon (FRP) refers to a sudden onset of activity in the erector spinae muscles that recedes or fades during full forward flexion of the trunk. Lumbar spine and hip flexion are associated with many daily physical activities that also impact trunk flexion. Shorter hamstring muscles result in a reduction of pelvic mobility that eventually culminates in low back pain (LBP). Many studies have explored the FRP in relation to LBP. However, few studies have investigated the influence of hamstring muscle length on the FRP in relation to the erector spinae muscles during trunk flexion. Objects: This study aimed to investigate the influence of hamstring muscle length on the FRP in relation to the erector spinae muscles during trunk flexion. Methods: Thirty subjects were divided into three groups according to hamstring length measured through an active knee extension test. The 30 participants consisted of 10 subjects who had a popliteal angle of 20˚ or less (Group 1), 10 subjects who had a popliteal angle of 21˚–39˚ (Group 2), and 10 subjects who had a popliteal angle of 40˚ or more (Group 3). A one-way analysis of variance was used to compare the difference in muscle activity of the erector spinae muscles during trunk flexion. Results: The subjects with a shorter hamstring length had significantly higher muscle activity in their erector spinae muscles during trunk flexion and full trunk flexion (p < 0.05). The subjects with a shorter hamstring length also had a significantly higher flexion-relaxation ratio (p < 0.05). Conclusion: The results of this study demonstrate that differences in hamstring muscle length can influence the FRP in relation to the erector spinae muscles. This finding suggests that the shortening of the hamstring might be associated with LBP.

Background: Although various exercises have been performed for patients with chronic low back pain (CLBP), the effects of these exercises including joint mobilization, gym ball exercises, and breathing exercises on flexion relaxation ratio (FRR) have not been compared. Objective: To compare the effects of joint mobilization, gym ball exercises, and breathing exercises on the flexion relaxation phenomenon (FRP) and pain in patients with chronic low back pain. Design: Randomized pretest-posttest control group design. Methods: Thirty-six patients with chronic low back pain who were undergoing rehabilitation at a rehabilitation center were included. The patients were randomly divided into three groups: joint mobilization group (JMG; n=12), gym ball exercise group (GBG; n=12), and breathing exercise group (BEG; n=12). The exercises were performed for 40 minutes a day, twice a week, for a total of 12 weeks. Results: There were no significant differences in FRR between the three groups (P>.05). Significant decreases in the modified visual analog scale (MVAS) scores after intervention between the groups were found (P<.05). The GBG was significantly decreases from the JMG in the MVAS (P<.05). However, there were significant improvements between the pre- and post-interventional findings on FRR and MVAS in the three groups (P<.05). Conclusion: We demonstrated that intervention using joint mobilization, gym ball exercises, and breathing exercises improve FRP and pain in patients with CLBP.

Background: Most of the previous researches on the abnormality of breathing pattern have focused on the silence of functional movements owing to such abnormality, however, have not been clearly identified the relationship between the abnormal breathing pattern on one hand and kinesiophobia and flexion relaxation phenomenon (FRP) on the other hand. Objective: To compare patients with chronic low back pain (CLBP) and healthy person in the abnormality of breathing pattern, kinesiophobia, and FRP during flexion and extension of the trunk. Design: Case-control study. Methods: The research subjects consisted of a group of 15 healthy adults and another group of 15 patients with CLBP. Capnography was used to measure the endtidal CO2 (EtCO2) and respiratory quotient (RQ). The muscle activity of multifidus and erector spinae of the subjects was measured during flexion and extension of the trunk to identify their FRP. The Nijmegen Questionnaire (NQ) and Tampa Scale of Kinesiophobia (TSK) were utilized to measure their breathing patterns and kinesiophobia, respectively. The Kolmogorov-Smirnov (K-S) test was conducted in order to analyze the normal distribution of the measured data. Their general characteristics were identified by the descriptive statistics and the independent t-test was performed to identify the differences between the two groups in terms of abnormality of breathing pattern, kinesiophobia, and FRP. The level of significance was set at α=.05. Results: The patients with CLBP had significantly less EtCO2 and shorter breathing hold time (BHT) than normal healthy person (p<.05). The patient with CLBP also had significantly greater kinesiophobia than healthy person (p<.05), and had less FRP than the healthy person (p<.01). Conclusions: These results suggest that the CLBP had greater abnormality of breathing pattern and kinesiophobia with less FRP than healthy person.