title: Modulation of intrinsic and reflexive contributions to low-back stabilization due to vision, task instruction, and perturbation bandwidth.
abstract: The goal of this study is to assess how reflexes and intrinsic properties contribute to low-back stabilization and modulate with conditions. Upper body sway was evoked by anterior-posterior platform translations, while subjects were seated with a restrained pelvis and free upper body. Kinematic analysis of trunk translations and rotations illustrated that a fixed rotation point between the vertebrae L4 and L5 adequately captures lumbar bending up to 5 Hz. To investigate the motor control modulation, the conditions varied in vision (eyes open or closed), task instruction (Balance naturally or Resist perturbations by minimizing low-back motions), and perturbation bandwidth (from 0.2 up to 1, 3 or 10 Hz). Frequency response functions and physiological modeling parameters showed substantial modulation between all conditions. The eyes-open condition led to trunk-in-space behavior with additional long-latency visual feedback and decreased proprioceptive feedback. The task instruction to resist led to trunk-on-pelvis stabilization behavior, which was achieved by higher co-contraction levels and increased reflexive velocity feedback. Perturbations below the low-back natural frequency (~1 Hz) led to trunk-on-pelvis stabilization behavior, mainly attributed to increased intrinsic damping. This indicates that bandwidth effects should not be ignored and that experiments with high-bandwidth perturbations do not fully represent the intrinsic and reflexive behavior during most (low-bandwidth) daily life activities. The neck stabilized the head orientation effectively (head rotation amplitudes 2 % of trunk), but did not effectively stabilize the head in space (global head translations exceeded trunk translations by 20 %). This indicates that low-back motor control is involved in head-in-space stabilization and could explain the low-back motor control modulations due to vision.
authors.affiliation: BioMechanical Engineering Department, Faculty of Mechanical Engineering, Delft University of Technology, Mekelweg 4, 2628 CD, Delft, The Netherlands, P.vanDrunen@TUDelft.nl.
authors.forename: P
authors.initials: P
authors.lastname: van Drunen
authors.forename: Y
authors.initials: Y
authors.lastname: Koumans
authors.forename: F C T
authors.initials: FC
authors.lastname: van der Helm
authors.forename: J H
authors.initials: JH
authors.lastname: van Dieën
authors.forename: R
authors.initials: R
authors.lastname: Happee
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001415:Back / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology*; D008159:Lumbar Vertebrae; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D009949:Orientation / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D055815:Young Adult