Application of a novel force-field to manipulate the relationship between pelvis motion and step width in human walking

Abstract

The motion of the pelvis is typically linked to step width during human walking. This behavior is often considered an important component of ensuring bipedal stability, but can be disrupted in populations with neurological injuries. The purpose of this study was to determine whether a novel force-field that exerts mediolateral forces on the legs can manipulate the relationship between pelvis motion and step width, providing proof-of-concept for a future clinical intervention. We designed a force-field able to: 1) minimize the delivered mediolateral forces (Transparent mode); 2) apply mediolateral forces to assist the leg toward mechanically-appropriate step widths (Assistive mode); and 3) apply mediolateral forces to perturb the leg away from mechanically-appropriate step widths (Perturbing mode). Neurologically intact participants were randomly assigned to either the Assistive group (n=12) or Perturbing group (n=12), and performed a series of walking trials in which they interfaced with the force-field. We quantified the step-by-step relationship between mediolateral pelvis displacement and step width using partial correlations. Walking in the Transparent force-field had a minimal effect on this relationship. However, force-field assistance directly strengthened the relationship between pelvis displacement and step width, whereas force-field perturbations weakened this relationship. Both assistance and perturbations were followed by short-lived effects during a wash-out period, in which the relationship between pelvis displacement and step width differed from the baseline value. The present results demonstrate that the link between pelvis motion and step width can be manipulated through mechanical means, which may be useful for retraining gait balance in clinical populations.

Altered active control of step width in response to mediolateral leg perturbations while walking

“…As in previous work [2][3], we here performed linear regressions with mediolateral pelvis displacement and velocity as independent variables, and step width as the dependent variable. The R 2 value resulting from this regression was used to quantify the strength of the relationship between pelvis motion and step width.…”

Effects of targeted assistance and perturbations on the relationship between pelvis motion and step width in people with chronic stroke

“…The force-field used to exert mediolateral forces on participants' legs has been described in detail previously. 14,24 Briefly, forces are applied using steel wires running parallel with the treadmill belts and in series with extension springs. The wires pass The Transparent mode was designed to minimize the mediolateral leg forces experienced by users, as the force-field wires were continuously repositioned to stay aligned with the corresponding leg cuff.…”

“…12 Given the post-stroke deficits in the foot placement gait stabilization strategy, we have developed a novel force-field to manipulate the relationship between pelvis motion and step width. [13][14] In neurologically-intact controls, we have used this force-field to assist appropriate mediolateral foot placement, encouraging wide steps when the pelvis is displaced far from the stance foot and narrow steps when the pelvis is close to the stance foot. This approach is based on the proposal that assisting a movement pattern can strengthen an individual's ability to perform this movement independently, due in part to enhanced sensory feedback.…”

“…17 Here, we found that force-field perturbations directly decreased ρdisp, weakening the link between pelvis displacement and step width. 14…”

Risk-of-falling related outcomes improved in community-dwelling older adults after a 6-week sideways walking intervention: a feasibility and pilot study

“…Currently, external stabilization devices and body weight support systems can be used to o oad the need of active control and decrease the amount of step width variability during walking [24,[42][43][44][45]. This has implications for walking stability intervention in older adults, which could be directed to exploit the mechanical features of gait dynamics, such as motion-dependent torques [46]. Previous studies showed that passive dynamics are less sensitive to age-related de ciencies of active control or the lack thereof [23,28,29].…”