Automatic postural responses are scaled from the association between online feedback and feedforward control

Abstract

Generation of automatic postural responses (APRs) scaled to magnitude of unanticipated postural perturbations is required to recover upright body stability. In the current experiment, we aimed to evaluate the effect of previous postural perturbations on APR scaling under conditions in which the current perturbation is equal to or different from the previous perturbation load inducing unanticipated forward body sway. We hypothesized that the APR is scaled from the association of the current perturbation magnitude and postural responses to preceding perturbations. Evaluation was made by comparing postural responses in the contexts of progressive increasing versus decreasing magnitudes of perturbation loads. Perturbation was applied by unanticipatedly releasing a cable pulling the body backwards, with loads corresponding to 6%, 8% and 10% of body mass. We found that the increasing as compared to the decreasing load sequence led to lower values of (a) displacement and (b) velocity of center of pressure, and of activation rate of the muscle gastrocnemius medialis across loads. Muscular activation onset latency decreased as a function increasing loads, but no significant effects of load sequence were found. These results lead to the conclusion that APRs to unanticipated perturbations are scaled from the association of somatosensory feedback signaling balance instability with feedforward control from postural responses to previous perturbations.

Judokas Show Increased Resilience to Unpredictable Stance Perturbations

“…This training-related modulation of reflex activation can be thought to underlie attenuation of exaggerated limb movements in response to sudden perturbations, at the same time that favors more accurate muscular activation from supra-spinal control centers (Taube et al, 2008). At higher order control centers, evidence of increased activation of the prefrontal and parietal cortices following perturbation-based dynamic balance training (Patel et al, 2018) and increased connectivity between those cortical areas as a result of randomly scheduled practice (Lin et al, 2013), may lead to adaptive selection and scaling of compensatory movements to deal with balance perturbations whose demands cannot be anticipated (Takazono et al, 2020; Teixeira, Maia Azzi, et al, 2020). From the current results, we suggest that the discussed adaptations at lower and higher levels of control to perturbation-based balance training are developed by judokas during their training when responding to unpredictable perturbations in combat-like activities.…”

Vertical ground reaction force oscillation during standing on hard and compliant surfaces: The “postural rhythm”

“…On compliant surface, the feedback would recruit several body muscles ( 20 , 75 , 118 , 132 – 134 ) and operate together with anticipatory activations ( 135 , 136 ). This interaction would be modulated by the sensory inputs and efference copies connected with the continuous body sway and muscle actions, respectively ( 137 ).…”

Reactive Response of Older Tennis Practitioners and Healthy Young People in Relation to Balance Perturbations

“…Fifteen young people (age 23.00 ± 1.96 years; body mass 67.78 ± 11.11 kg; height 1.69 ± 0.10 m; 7 men, 8 women) participated in the study as self-declared non-practitioners of regular physical activity for more than 1 year and 12 older people (age 69.08 ± 3.82 years; body mass 75.09 ± 14.14 kg; height 1.66 ± 0.08 m; ten men, two women), self-declared tennis players for over 2 years and practice three times a week at least 1 h per session. The sample size was based on similar studies [2,26,30]. Participants were recruited through local advertising and were selected only if they were defined as "medically stable" according to Greig et al [8].…”

“…APRs are identified by small postural adjustments and muscle and motor activity in the 100 ms before a perturbation occurs [17], and their fundamental role is to minimize a probable imbalance caused by a predictable postural perturbation. APRs are generated through the feedforward system, which in the literature is defined as the ability to modulate responses based on information retained by previous experience [30]. CPRs are identified through muscle activation and oscillation strategies that follow the postural perturbation, minimizing the disturbance caused by the perturbation, and this strategy is triggered by predictable and unpredictable perturbations [4].…”