A method for lower back motion assessment using wearable 6D inertial sensors

Marco Molnar, Manon Kok, Tilman Engel, Hannes Kaplick, Frank Mayer, Thomas Seel

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

2 Citations (Scopus)
43 Downloads (Pure)


Low back pain (LBP) is a leading cause of activity limitation. Objective assessment of the spinal motion plays a key role in diagnosis and treatment of LBP. We propose a method that facilitates clinical assessment of lower back motions by means of a wireless inertial sensor network. The sensor units are attached to the right and left side of the lumbar region, the pelvis and the thighs, respectively. Since magnetometers are known to be unreliable in indoor environments, we use only 3D accelerometer and 3D gyroscope readings. Compensation of integration drift in the horizontal plane is achieved by estimating the gyroscope biases from automatically detected initial rest phases. For the estimation of sensor orientations, both a smoothing algorithm and a filtering algorithm are presented. From these orientations, we determine three-dimensional joint angles between the thighs and the pelvis and between the pelvis and the lumbar region. We compare the orientations and joint angles to measurements of an optical motion tracking system that tracks each skin-mounted sensor by means of reflective markers. Eight subjects perform a neutral initial pose, then flexion/extension, lateral flexion, and rotation of the trunk. The root mean square deviation between inertial and optical angles is about one degree for angles in the frontal and sagittal plane and about two degrees for angles in the transverse plane (both values averaged over all trials). We choose five features that characterize the initial pose and the three motions. Interindividual differences of all features are found to be clearly larger than the observed measurement deviations. These results indicate that the proposed inertial sensor-based method is a promising tool for lower back motion assessment.

Original languageEnglish
Title of host publicationProceedings of the 21st International Conference on Information Fusion 2018 (FUSION 2018)
Place of PublicationPiscataway, NJ, USA
ISBN (Electronic)978-0-9964527-7-9
ISBN (Print)978-0-9964527-6-2
Publication statusPublished - 2018
Event21st International Conference on Information Fusion, FUSION 2018 - Cambridge, United Kingdom
Duration: 10 Jul 201813 Jul 2018


Conference21st International Conference on Information Fusion, FUSION 2018
CountryUnited Kingdom

Bibliographical note

Accepted Author Manuscript


  • avoid magnetometers
  • back motion assessment
  • drift correction
  • human motion analysis
  • Inertial measurement units
  • joint angle estimation
  • low back pain
  • validation against optical motion capture


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