A neuromechanical strategy for mediolateral foot placement in walking humans.
Stability is an important concern during human walking and can limit mobility in clinical populations. Mediolateral stability can be efficiently controlled through appropriate foot placement, although the underlying neuromechanical strategy is unclear. We hypothesized that humans control mediolateral foot placement through swing leg muscle activity, basing this control on the mechanical state of the contralateral stance leg. Participants walked under Unperturbed and Perturbed conditions, in which foot placement was intermittently perturbed by moving the right leg medially or laterally during the swing phase (by ∼50-100 mm). We quantified mediolateral foot placement, electromyographic activity of frontal-plane hip muscles, and stance leg mechanical state. During Unperturbed walking, greater swing-phase gluteus medius (GM) activity was associated with more lateral foot placement. Increases in GM activity were most strongly predicted by increased mediolateral displacement between the center of mass (CoM) and the contralateral stance foot. The Perturbed walking results indicated a causal relationship between stance leg mechanics and swing-phase GM activity. Perturbations that reduced the mediolateral CoM displacement from the stance foot caused reductions in swing-phase GM activity and more medial foot placement. Conversely, increases in mediolateral CoM displacement caused increased swing-phase GM activity and more lateral foot placement. Under both Unperturbed and Perturbed conditions, humans controlled their mediolateral foot placement by modulating swing-phase muscle activity in response to the mechanical state of the contralateral leg. This strategy may be disrupted in clinical populations with a reduced ability to modulate muscle activity or sense their body's mechanical state.
Division of Physical Therapy, College of Health Professions, Medical University of South Carolina, Charleston, South Carolina; and.
Bradford L
BL
Rankin
Division of Physical Therapy, College of Health Professions, Medical University of South Carolina, Charleston, South Carolina; and.
Stephanie K
SK
Buffo
Division of Physical Therapy, College of Health Professions, Medical University of South Carolina, Charleston, South Carolina; and Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, South Carolina deaje@musc.edu.
Jesse C
JC
Dean
D001696:Biomechanical Phenomena; D005260:Female; D005684:Gait; D006801:Humans; D007866:Leg / Q000294:innervation / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D016138:Walking / Q000502:physiology*; D055815:Young Adult
biomechanics; locomotion; muscle activity; stability