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.

Segmental trunk and head dynamics during frontal plane tilt stimuli in healthy sitting adults

“…The bandwidth was 0.046–4.9 Hz and cycle duration was 21.78 s. Assessing balance across multiple frequencies enables a more comprehensive characterization of the balance system (Pintelon and Schoukens, 2012). The surface tilt signals contained less power across higher frequencies compared to previous studies (Goodworth and Peterka, 2009; van Drunen et al, 2015). The stimuli in each test consisted of 5 to 8 repeated cycles of a PRTS waveform (Figure 2A).…”

Reliability of assessing postural control during seated balancing using a physical human-robot interaction

“…Future work should investigate how much practice is needed to converge on relatively stable performance. Moreover, learning may be due to modulations in the contributing pathways (van Drunen et al, 2015) (e.g., intrinsic and vestibular pathways in the VIB condition). Future work should investigate such pathways by using parametric models.…”

“…Thus, data reproducibility and test reliability may vary from one study to another. To overcome this problem, we developed a physical human-robot interaction (pHRI) system (Priess et al, 2015) that consists of a compliant unstable seat and, at the same time, provides torque perturbation as a known input to the system (Cruise et al, 2017; van Drunen et al, 2016, 2015, 2013). This pHRI also allows for the precise regulation of test difficulty by controlling rotational seat stiffness.…”

Neck postural stabilization, motion comfort, and impact simulation

“…As outlined in this paragraph, knowledge and models of postural stabilization and the resulting head motion are essential in the domain of motion comfort, particularly in self-driving vehicles. In automated vehicles, we may use the travel time for work or leisure activities (Kyriakidis, Happee, & De Winter 2015), but this requires high comfort levels, where self-driving car sickness is a particular concern (Diels & Bos, 2016). Hence we need to carefully design the "driving style" of automated vehicles (Bellem, Schönenberg, Krems, & Schrauf, 2016).…”

“…Motion sickness is primarily caused by motion frequencies below 0.5 Hz while frequencies above 0.5 Hz can elicit general vibration discomfort (ISO-2631(ISO- -1, 1997. The act of driving makes drivers virtually insensitive to motion sickness, whereas passengers typically suffer more, especially when deprived of visual information about self-motion obtained from views out of the window (Diels & Bos, 2016). Current standards assess the overall vibration discomfort of seated people by summation of frequency-weighted accelerations at the seat, the back, and the feet (British Standards Institution, 1987;ISO-2631ISO- -1, 1997.…”