• Physical Therapy Korea
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• v.24 no.4
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• pp.1-10
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• 2017

Background: Flexion-relaxation phenomenon (FRP) was a term which refers to a sudden onset of myoelectric silence in the erector spinae muscles of the back during standing full forward flexion. Hamstring muscle length may be related to specific pelvic and trunk movements. Many studies have been done on the FRP of the erector spinae muscles. However, no studies have yet investigated the influence of hamstring muscle flexibility on the FRP of the hamstring muscle and lumbopelvic kinematics during forward bending. Objects: The purpose of this study was to examine the flexion-relaxation ratio (FRR) of the hamstring muscles and lumbopelvic kinematics and compare them during forward bending in subjects with different hamstring muscle flexibility. Methods: The subjects of two different groups were recruited using the active knee extension test. Group 1-consisted of 13 subjects who had a popliteal angle under $30^{\circ}$; Group 2-consisted of 13 subjects who had a popliteal angel above $50^{\circ}$. The kinematic parameters during the trunk bending task were recorded using a motion analysis system and the FRRs of the hamstring muscles were calculated. Differences between the groups were identified with an independent t-test. Results: The subjects with greater hamstring length had significantly less lumbar spine flexion movement and more pelvic flexion movement. The subjects with greater pelvic flexion movement had a higher rate of flexion relaxation during full trunk bending (p<.05). Conclusion: The results of this study suggest that differences in hamstring muscle flexibility might cause changes in people's hamstring muscle activity and lumbopelvic kinematics.

• PNF and Movement
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• v.13 no.4
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• pp.197-202
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• 2015

Purpose: This study aimed to examine the effects of a proprioceptive neuromuscular facilitation (PNF) program on neck pain, cervical range of motion, pressure pain, and the cervical flexion-relaxation ratio in a visual display terminal (VDT) worker. Methods: We recruited a 33-year-old VDT worker diagnosed with chronic VDT syndrome. The subject was treated using a PNF program for 20 minutes a day, three times a week for six weeks. All evaluations were performed every two weeks on the first test day. Results: The PNF program resulted in a significant improvement in the subject's neck pain, cervical range of motion, pressure pain, and the cervical flexion-relaxation ratio after six weeks, in comparison to the subject's condition before treatment. Conclusion: The PNF program can be used effectively to improve neck pain, cervical range of motion, pressure pain, and the cervical flexion-relaxation ratio in visual display terminal (VDT) workers.

• The Journal of Korean Physical Therapy
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• v.32 no.6
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• pp.378-382
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• 2020

Purpose: This study aimed to examine the effects of forward head posture on the flexion-relaxation ratio (FRR) and muscle activity during sustained neck flexion and to investigate the correlation between craniovertebral angle and FRR. Methods: Nineteen subjects participated in this study and were allocated to a forward head posture (FHP) group or a non-forward head posture (NFHP) group. Craniovertebral angle (CVA) and FRR were measured in all subjects, and all participants performed a standardized cervical flexion-extension movement in two phases: Phase I, sustained cervical full flexion for 5s; and Phase II, cervical extension with the return to the starting position for 5s. The value of CVA has calculated three times, and the value of FRR was measured three times in order to obtain the mean value. Results: FRR values in the FHP and NFHP group were significantly different (p<0.05). Phase I was significantly different, but the Phase II was not significantly different between the FHP and NFHP group (p>0.05). There was a significant correlation between the muscle activity of Phase I and CVA (p<0.05). However, FRR and the muscle activity of the Phase II were not a significant correlation with the CVA (p>0.05). Conclusion: FHP increases the muscle activity of the cervical erector spinae during sustained neck flexion and reduces FRR, which can cause fatigue in the cervical erector spinae. In addition, for those with a smaller CVA, muscle activity of the cervical erector spinae is increased during sustained neck flexion, which can increase neck muscle tension.

• Physical Therapy Korea
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• v.27 no.3
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• pp.171-177
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• 2020

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.

• Journal of International Academy of Physical Therapy Research
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• v.11 no.1
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• pp.1981-1991
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• 2020

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.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.217-222
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• 1995

We propose some applications of image processing techniques to extract quantitative measurements by using a camera system developed in Korea university and Catholic Medical School. From now on the system will be called as KCMOTION. The purpose of this study is to provide basic kinematic and kinetic data for the analysis of human movements and to find the clinical usefulness and reliability of the proposed motion analysis system. Two tests, sit-to-stand (STS) movements and pendulum test, are conducted by the system. The aims of the tests are to identify variability and reliability of KCMOTION to give some quantitative comparisons to the other systems. The result of STS movement are compared to the LOCUS IIID motion analyzer by the ratio of maximum flexion movement per body weight to the actual maximum flexion extension torque per body weight. That result in 29 % and 33 % for hip and knee joint, respectively in KCMOTION and 27 % and 30 % in LOCUS IIID System. The results of the pendulum movements are compared to that of using Cybex and Electrogoniometer with relaxation index, amplitude ratio, swing number and swing time. The results of relaxation index and amplitude ratio of the KCMOTION are between those of the Cybex and Electrogoniometer. We also observed that the KCMOTION detect more natural movement, from the results of swing number and time.

• PNF and Movement
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• v.19 no.3
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• pp.413-422
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• 2021

Purpose: This study was conducted to investigate changes in the cervical and lumbar flexion-relaxation ratio, range of motion, pressure pain threshold, and perceived comfort following the wearing of a trunk brace during smartphone watching. Methods: To calculate the number of subjects for this study, an analysis with G^*Power was performed at a statistical power of 0.8, an effect size of 0.5, and a significance level of 0.05, based on the results of a preliminary experiment on five subjects. In total, 27 adult men and women were recruited who had been informed of the study's purpose and process and had agreed to participate. All subjects watched content on a smartphone for 20 minutes in the same posture and conditions while wearing and not wearing a trunk brace, and then their cervical and lumbar flexion-relaxation ratio, range of motion, pressure pain threshold, and perceived comfort were measured. Results: Compared to the non-wearing of a trunk brace, the wearing of a trunk brace resulted in a statistically significant smaller decline in cervical extension and right-side cervical rotation (p<0.05). When the subjects wore a trunk brace, their right- and left-side cervical and right-side lumbar pressure pain statistically significantly improved when compared to not wearing a trunk brace (p<0.05). They also perceived a significantly lowered level of comfort 20 minutes after wearing a trunk brace compared to immediately after wearing it (p<0.05). Conclusion: The trunk brace was effective in reducing declines in right-side cervical rotation and the occurrence of left- and right-side cervical and right-side lumbar pressure pain. The findings indicate the need to improve the perceived comfort of trunk braces.

• Journal of The Korean Society of Integrative Medicine
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• v.7 no.1
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• pp.125-134
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• 2019

Purpose : The purpose of this study was to investigate the effects of stabilization exercise and breathing exercise on the flexion relaxation phenomenon (FRP) and respiratory parameters in patients with chronic low back pain. Methods : We randomly allocated 30 chronic low back pain patients (CLBP) to a stabilization exercise (SE) group (n=15) and a breathing exercise (BE) group (n=15). FRP was measured using surface electromyography (SEMG). Thoracic excursion was measured with a cloth tape measurement technique. The SE group participated in a stabilization exercise program and the BE group participated in a breathing exercise program three times a week for 12 weeks. The data was analyzed using paired t-tests for comparisons of flexion relaxation ratio (FRR) and respiratory variables. Independent t-tests were used for comparison of inter-group FRR and respiratory variables. The significance level was set at .05. Results : FRP variables-ES FRR (Flex/MVF), ES FRR (Ext/MVF), MF FRR (Flex/MVF), and MF FRR (Ext/MVF) values-increased significantly after exercise in both the SE and BE groups (p<.05). The thoracic excursion measurements after exercise increased significantly in both groups (p<.001). VAS values decreased significantly in both groups (p<.001). There were no significant differences between the two groups in FRP variables-ES FRR (Flex/MVF), ES FRR (Ext/MVF), MF FRR (Flex/MVF), and MF FRR (Ext/MVF)-or VAS values after exercise (p>.05). For thoracic excursion after exercise, the BE group was significantly higher than the SE group (p<.001). Conclusion : We found that FRP and respiratory variables increased significantly after SE and BE for 12 weeks in CLBP. Thoracic excursion-a respiratory variable-suggests that treatment was more effective in the BE group than the SE group.

• PNF and Movement
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• v.19 no.3
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• pp.375-382
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• 2021

Purpose: The objectives of the present study were to investigate the disadvantages of tire pressure asymmetry of a wheelchair tire and recommend the criterion for appropriate tire pressure without generating negative changes in the musculoskeletal system in asymptomatic participants. Methods: Fourteen asymptomatic participants were asked to sit in pressure-controlled wheelchairs and perform desk work for 20 minutes in each tire condition. The asymmetry of the tire conditions was set as 0% difference, 25% difference, and 50% difference from the recommended pressure. The pelvic alignment and muscular recruitment represented as a flexion-relaxation ratio (FRR) were measured at pre-test, and after each condition of desk work. The displacement of the center of pressure (COP) was measured during the desk work. Results: The tire air pressure condition significantly affected the FRR and COP (P < 0.05). Both sides of the FRR values were significantly higher under the symmetrical tire conditions (0% difference) and pre-test, compared with the asymmetrical tire condition of 50% difference (P < 0.05). The mediolateral COP displacement of the asymmetrical tire conditions (25% and 50% difference) was significantly higher than that of the symmetrical tire conditions (0%) (P < 0.05). Conclusion: Asymmetrical tire conditions could cause changes in the muscle recruitment pattern of the erector spine and mediolateral COP displacement. Tire pressure asymmetry higher than 50% could be a risk factor for prevalence of back pain, so this level of asymmetry in tire pressures should be cautioned against for wheelchair users.

• Korean Journal of Applied Biomechanics
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• v.33 no.1
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• pp.1-9
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• 2023

Objective: This study identifies the difference among the heights of a chair's backrest (High, Mid, No), the biomechanical changes chair users undergo over time, and the variables that can measure musculoskeletal disorders, eventually providing information on the appropriate type of backrest. Method: Eleven healthy subjects in their 20s and 30s who had no experience with musculoskeletal disorders or surgical operations within the last 6 months participated in this study. Computer typing tasks were randomly designated and performed according to the type of chair backrest, and evaluation was performed for Flexion-Relaxation Ratio (FRR) analysis after the computer typing tasks. This study used eight infrared cameras (sampling rate: 100 Hz) and nine-channel electromyography (sampling rate: 1,000 Hz). ANOVA with repeated measures was conducted to verify the results, with the statistical significance level being α = .05. Results: Although there was no significant difference in craniovertebral angle (CVA), this study showed time and interaction effects depending on the height of the backrest (p<.05). When working without the backrest, the head-spine angle was lower compared to the chairs with backrest, based on the computer work. As for the head angle, the higher the back of the chair was, the less the head flexion and the body angle became, whereas the body flexion became less when there was a backrest. In addition, the body flexion increased over time in all types of backrests (p<.05). The muscle activity of the upper body tended to be high in the high backrest chair. On the other hand, a lower muscle activity was found with a low backrest. Conclusion: These results show that a chair is more ergonomic when the body angle is correctly set without bending and when it is supported by a low backrest. Accordingly, this study determines that the backrest affects shoulder and neck musculoskeletal disorders during typing and that medium-height backrest chairs can help prevent musculoskeletal disorders, contrary to the expectation that high-backrest chairs are preferable.