Perturbation recovery during walking is impacted by knowledge of perturbation timing in below-knee prosthesis users and non-impaired participants

Abstract

Previous research found that below-knee prosthesis users proactively increase their lateral margin-of-stability on their impaired side in anticipation of an impending perturbation when the timing is predictable and potentially directed toward the impaired limb. While knowledge of perturbation timing and direction influences proactive strategies, the consequences of such knowledge and anticipatory behavior on recovery from perturbations is unclear. This study characterized center-of-mass (CoM) dynamics of below-knee prosthesis users and non-impaired controls following a lateral perturbation when the perturbation direction is known but a priori knowledge of the timing of perturbation is either known or unknown. Across groups, CoM displacement during perturbation exposure increased when directed towards the impaired or non-dominant limb with no influence of timing knowledge. In addition, peak CoM displacement was less with known timing irrespective of the perturbation direction. Generally, the CoM displacement during perturbation exposure correlated well with the CoM medial-lateral velocity during unperturbed walking, supporting evidence that human response dynamics to lateral perturbations are influenced by the instantaneous state of the body’s momentum.

Dynamic balancing responses in unilateral transtibial amputees following outward-directed perturbations during slow treadmill walking differ considerably for amputated and non-amputated side

“…However the findings of the present study seems to only partially conform to the results of other studies that have investigated dynamic balancing responses following unexpected perturbing pushes in the frontal plane applied to the pelvis of UTA subjects [ 23 , 24 ]. Namely UTA subjects in those studies developed stepping responses regardless whether the non-amputated or amputated leg was in stance phase at the time of perturbation [ 23 , 24 ] whereas in the present study UTA subjects applied in-stance and not stepping strategy when they counteracted outward-directed perturbation on the non-amputated side. Discrepancy between studies is to be attributed to different walking speeds which was in those studies 0.8 m/s whereas in in the present study it was set to 0.5 m/s to match the average walking speed of UTA subjects after discharge [ 1 ].…”

“…Unlike proactive gait adaptations reactive responses of UTA subjects have been addressed in the literature less extensively. Experiments where perturbing pushes were delivered to the pelvis in the frontal plane [ 23 , 24 ] showed that UTA subjects use proactive adaptations only if the timing of perturbation is predictable and when perturbation is delivered on their amputated side [ 23 ]. They also showed that if perturbation timing is known peak COM displacement is smaller [ 24 ].…”

“…Experiments where perturbing pushes were delivered to the pelvis in the frontal plane [ 23 , 24 ] showed that UTA subjects use proactive adaptations only if the timing of perturbation is predictable and when perturbation is delivered on their amputated side [ 23 ]. They also showed that if perturbation timing is known peak COM displacement is smaller [ 24 ]. However if the timing of perturbation is not known in advance no proactive adaptations took place and unexpected perturbations had to be negotiated purely through reactive feedback mechanisms [ 23 , 24 ].…”

“…They also showed that if perturbation timing is known peak COM displacement is smaller [ 24 ]. However if the timing of perturbation is not known in advance no proactive adaptations took place and unexpected perturbations had to be negotiated purely through reactive feedback mechanisms [ 23 , 24 ]. Similar studies where UTA subjects were subjected to unexpected medio-lateral foot placement perturbation showed an important role of hip strategies in recovering balance [ 29 ].…”

“…These studies explored dynamic balancing responses of UTA subjects at relatively high walking speed: 0.8 m/s [ 23 , 24 ] and 1.2 m/s [ 2 , 13 , 29 ]. To the best of our knowledge we are not aware of any study that has investigated dynamic balance of UTA subjects at slow walking, e.g.…”