Biology subjects

van Dieen, J. H.

Publications and source records attributed to van Dieen, J. H..

3 recordsLinked to original sources

bioRxiv2020

Stabilization demands of walking modulate the vestibular contributions to gait

Stable walking relies critically on motor responses to signals of head motion provided by the vestibular system, which are phase-dependent and modulated differently within each muscle. It is unclear, however, whether these vestibular contributions also vary according to the stability of the walking task. Here we investigate how vestibular signals influence muscles relevant for gait stability (medial gastrocnemius, gluteus medius and erector spinae) - as well as their net effect on ground reaction forces - while humans walked normally, with mediolateral stabilization, wide and narrow steps. We estimated local dynamic stability of trunk kinematics together with coherence of electrical vestibular stimulation (EVS) with muscle activity and mediolateral ground reaction forces. Walking with external stabilization increased local dynamic stability and decreased coherence between EVS and all muscles/forces compared to normal walking. Wide-base walking also decreased vestibulomotor coherence, though local dynamic stability did not differ. Conversely, narrow-base walking increased local dynamic stability, but produced muscle-specific increases and decreases in coherence that resulted in a net increase in vestibulomotor coherence with ground reaction forces. Overall, our results show that while vestibular contributions may vary with gait stability, they more critically depend on the stabilization demands (i.e. control effort) needed to maintain a stable walking pattern.

neuroscience↗

bioRxiv2020

The underlying mechanisms of improved balance aftershort- and long-term training in older adults

Training improves balance control in older adults, but the time course and neural mechanisms underlying these improvements are unclear. We studied balance robustness and performance, H-reflex gains, paired reflex depression, and co-contraction duration in ankle muscles after one and ten training sessions in 22 older adults (+65yrs). Mediolateral balance robustness, time to balance loss in unipedal standing on a platform with decreasing rotational stiffness, improved (33%) after one session, with no further improvement after ten sessions. Balance performance, absolute mediolateral center of mass velocity, improved (18.75%) after one session in perturbed unipedal standing and (18.18%) after ten sessions in unperturbed unipedal standing. Co-contraction duration of soleus/tibialis anterior increased (16%) after ten sessions. H-reflex gain and paired reflex depression excitability did not change. H-reflex gains were lower, and soleus/tibialis anterior co-contraction duration was higher in participants with more robust balance after ten sessions, and co-contraction duration was higher in participants with better balance performance at several time-points. Changes in robustness and performance were uncorrelated with changes in co-contraction duration, H-reflex gain, or paired reflex depression. In older adults, balance robustness improved over a single session, while performance improved gradually over multiple sessions. Changes in co-contraction and excitability of ankle muscles were not exclusive causes of improved balance. HighlightsO_LIBalance robustness and balance performance in perturbed unipedal standing was improved after one balance training session, with no further improvement after ten sessions. C_LIO_LIBalance performance in unperturbed unipedal standing was improved after ten sessions C_LIO_LIH-reflex and paired reflex depression did not change after training in unipedal or bipedal standing. C_LIO_LICo-contraction duration of antagonistic ankle muscles increased after ten sessions in perturbed and unperturbed unipedal standing. C_LIO_LIChanges in co-contraction duration and excitability of ankle muscles were not exclusive causes of improved balance. C_LI

neuroscience↗

bioRxiv2020

Step width and frequency to modulate: Active foot placement control ensures stable gait

Step-by-step foot placement control, relative to the center of mass (CoM) kinematic state, is generally considered a dominant mechanism for maintenance of gait stability. By adequate (mediolateral) positioning of the center of pressure with respect to the CoM, the ground reaction force generates a moment that prevents falling. In healthy individuals, foot placement is complemented mainly by ankle moment control ensuring stability. To evaluate possible compensatory relationships between step-by-step foot placement and complementary ankle moments, we investigated the degree of (active) foot placement control during steady-state walking, and under either foot placement-, or ankle moment constraints. Thirty healthy participants walked on a treadmill, while full-body kinematics, ground reaction forces and EMG activities were recorded. As a replication of earlier findings, we first showed step-by-step foot placement is associated with preceding CoM state and hip ab-/adductor activity during steady-state walking. Tight control of foot placement appears to be important at normal walking speed because there was a limited change in the degree of foot placement control despite the presence of a foot placement constraint. At slow speed, the degree of foot placement control decreased substantially, suggesting that tight control of foot placement is less essential when walking slowly. Step-by-step foot placement control was not tightened to compensate for constrained ankle moments. Instead compensation was achieved through increases in step width and stride frequency.

neuroscience↗