title: Individual characteristics of reliable lumbar coupling motions.
abstract: BACKGROUND
  Coupling motions (CMs) are the motions occurring in different directions around the primary motion. As low back pain (LBP) is known to be associated with lumbar CMs, some studies measured lumbar CMs using the microelectromechanical system inertial measurement unit (MEMS-IMU) because of its low cost and small size. This study aimed to examine the reliability of lumbar CM measurements using the MEMS-IMU and to classify the individual characteristics of lumbar CMs.
  
  
  METHODS
  MEMS-IMUs were attached to the two lumbar points (L₁, L₅) of 19 male volunteers (age, 24.3 ± 1.2 years). Following an instructional video and audio recording, they conducted the six lumbar movements three times: flexion and extension, left and right lateral bending, and left and right rotation. The six lumbar movements were repeated after 1 h. Raw data were transformed into angle data using MATLAB. Intraclass correlation coefficients (ICCs) were calculated to evaluate intratest repeatability and test-retest reliability. Finally, angle data were analyzed to examine whether individual characteristics of lumbar CMs could be identified.
  
  
  RESULTS
  Lumbar CM measurements showed fair to good or excellent intratest repeatability and test-retest reliability, ranging from 0.669 to 0.997 of the ICCs. All lumbar CMs could be categorized into six types, and flexion and extension CMs were more prominent than other CMs.
  
  
  CONCLUSIONS
  Lumbar CM measurements obtained using the MEMS-IMU are reliable, and identifying the individual variations of lumbar CMs may be helpful for alleviating chronic or recurrent LBP.
authors.affiliation: Department of Human Informatics of Korean Medicine, Interdisciplinary Programs, Kyung Hee University, Seoul, Republic of Korea.
authors.forename: Woo-Suck
authors.initials: WS
authors.lastname: Yun
authors.forename: Hyunho
authors.initials: H
authors.lastname: Kim
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Ahn
authors.forename: Young-Bae
authors.initials: YB
authors.lastname: Park
authors.forename: Young-Jae
authors.initials: YJ
authors.lastname: Park
mesh_terms: D000328:Adult; D053587:Arthrometry, Articular / Q000379:methods; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012399:Rotation; D055815:Young Adult