Stabilization demands of walking modulate the vestibular contributions to gait

Abstract

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.

Effects of vestibular stimulation on gait stability when walking at different step widths

“…Other mechanisms are shifting the center of pressure under the stance foot (Reimann et al 2018;van Leeuwen et al 2021) and changing angular momentum around the CoM (Hof 2008;van den Bogaart et al 2020). The increase in EVS-erector spinae muscle coupling during narrow-base walking that we found previously (Magnani et al 2021), suggests that indeed angular momentum changes may play a larger role during narrowbase walking, as was also seen in behavioral studies (Bogaart et al 2021).…”

“…In line with this, vestibular evoked responses in ground reaction force and muscles activity are increased in magnitude when one is exposed to a postural threat (Horslen et al 2014;Naranjo et al 2015). In a recent study (Magnani et al 2021)., we showed that, compared to normal walking, mediolateral ground reaction forces were less coupled to vestibular stimulation when subjects were stabilized by means of elastic cords providing conservative forces to maintain the mediolateral position of the body CoM or when walking with wide steps.…”

“…Stochastic EVS has been shown to decrease gait stability (i.e. increase the local divergence exponent) (Sloot et al 2011;van Schooten et al 2011;Magnani et al 2021).…”

“…Moreover, a wider step width has been reported as a response to impaired lateral stability during locomotion (Kubinski et al 2015;Aboutorabi et al 2016). However, previous studies have also shown that local dynamic stability is reduced when walking with wider steps (Young and Dingwell 2012;Magnani et al 2021). Walking with wide steps requires less tight control (Perry and Srinivasan 2017), allowing people to be less stable (i.e.…”

Improvement in gait stability in older adults after ten sessions of standing balance training

“…We focused on changes in timing of muscle activation by assessing the synergy activation profiles’ full width at half maximum (FWHM), reflecting activation duration, and Center of Activation (CoA), reflecting time of peak activation. We hypothesized that adaptations to narrow-base walking would be reflected in enhanced gait stability [ 39 ] and in more prolonged muscle activation. Furthermore, we hypothesized that training effects would transfer to gait as reflected in improved gait stability and narrow-base walking performance and activation profiles with less prolonged muscle activation.…”