title: Complementary mechanisms for upright balance during walking.
abstract: Lateral balance is a critical factor in keeping the human body upright during walking. Two important mechanisms for balance control are the stepping strategy, in which the foot placement is changed in the direction of a sensed fall to modulate how the gravitational force acts on the body, and the lateral ankle strategy, in which the body mass is actively accelerated by an ankle torque. Currently, there is minimal evidence about how these two strategies complement one another to achieve upright balance during locomotion. We use Galvanic vestibular stimulation (GVS) to induce the sensation of a fall at heel-off during gait initiation. We found that young healthy adults respond to the illusory fall using both the lateral ankle strategy and the stepping strategy. The stance foot center of pressure (CoP) is shifted in the direction of the perceived fall by ≈2.5 mm, starting ≈247 ms after stimulus onset. The foot placement of the following step is shifted by ≈15 mm in the same direction. The temporal delay between these two mechanisms suggests that they independently contribute to upright balance during locomotion, potentially in a serially coordinated manner. Modeling results indicate that without the lateral ankle strategy, a much larger step width is required to maintain upright balance, suggesting that the small but early CoP shift induced by the lateral ankle strategy is critical for upright stability during locomotion. The relative importance of each mechanism and how neurological disorders may affect their implementation remain an open question.
authors.affiliation: Department of Kinesiology, Temple University, Philadelphia, PA, United States of America.
authors.forename: Hendrik
authors.identifier: http://orcid.org/0000-0002-3418-9345
authors.initials: H
authors.lastname: Reimann
authors.affiliation: Department of Kinesiology, Temple University, Philadelphia, PA, United States of America.
authors.forename: Tyler D
authors.initials: TD
authors.lastname: Fettrow
authors.affiliation: Department of Kinesiology, Temple University, Philadelphia, PA, United States of America.|Department of Physical Therapy, Temple University, Philadelphia, PA, United States of America.
authors.forename: Elizabeth D
authors.initials: ED
authors.lastname: Thompson
authors.affiliation: Department of Kinesiology, Temple University, Philadelphia, PA, United States of America.
authors.forename: Peter
authors.initials: P
authors.lastname: Agada
authors.affiliation: Centre for Interdisciplinary Research in Rehabilitation and Social Integration, Université Laval, Québec, Canada.|Department of Rehabilitation, Université Laval, Québec, Canada.
authors.forename: Bradford J
authors.initials: BJ
authors.lastname: McFadyen
authors.affiliation: Department of Kinesiology, Temple University, Philadelphia, PA, United States of America.
authors.forename: John J
authors.initials: JJ
authors.lastname: Jeka
mesh_terms: D000328:Adult; D000842:Ankle / Q000502:physiology; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000502:physiology; D005684:Gait / Q000502:physiology*; D006801:Humans; D008124:Locomotion / Q000502:physiology; D008297:Male; D009068:Movement; D004856:Postural Balance; D011187:Posture / Q000502:physiology; D019415:Torque; D016138:Walking; D055815:Young Adult