PNF and Movement 2021; 19(3): 413-422
Changes in the Cervical and Lumber Flexion-Relaxation Ratio, Range of Motion, Pressure Pain Threshold, and Perceived Comfort Following the Wearing of a Trunk Brace during Smartphone Watching
Jin-Seong Park, P.T., Ph.D.⋅Du-Jin Park, P.T., Ph.D.1†
1Department of Physical Therapy, College of Health Sciences, Catholic University of Pusan
Correspondence to: Du-Jin Park (
Received: November 25, 2021; Revised: December 8, 2021; Accepted: December 9, 2021; Published online: December 31, 2021.
© Korea Proprioceptive Neuromuscular Facilitation Association. All rights reserved.

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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.
Keywords: Trunk brace, Smart phone, Neck, Lumbar

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