How do we tread? Differences in stability-related foot placement control between overground and treadmill walking in young adults.

A significant relationship between step width/step length and center-of-mass state during the swing phase was found during overground walking, captured by the same linear model used for treadmill walking.

• 14 young adults walked at comfortable walking speed both on a treadmill and overground in a figure-8 path
• The linear foot placement control model previously established for treadmill walking generalized to the overground condition
• Both step width and step length models showed significant relationships with center-of-mass state during swing phase

Foot placement precision was significantly lower during overground walking compared to treadmill walking for the step width model with center-of-mass state at the start of the swing phase as predictor.

• This finding was contrary to what was hypothesized
• The lower precision was specific to the step width model using center-of-mass state at the start of swing phase as predictor
• Lower foot placement precision indicates greater unexplained variability in step width relative to center-of-mass state

Average step width was significantly wider during overground walking compared to treadmill walking.

• The wider average step width during overground walking complemented the finding of lower foot placement precision
• Sample size was 14 young adults
• This difference in step width was observed at comfortable walking speed

During overground walking, participants responded significantly less strongly to deviations in center-of-mass position compared to treadmill walking.

• This reduced response to center-of-mass position deviations was found for both the step width and step length models
• The difference was observed at the end of the step
• This finding applied to both the step width and step length foot placement control models

During overground walking, participants responded significantly more strongly to deviations in center-of-mass velocity compared to treadmill walking.

• Stronger velocity feedback responses were found for both the step width and step length models
• The enhanced response to center-of-mass velocity was measured at the end of the step
• Exploratory analysis showed a larger relative contribution of velocity feedback during overground walking as compared to treadmill walking

Current understanding of foot placement mechanisms is primarily based on treadmill walking findings, which may not generalize to overground walking and daily life gait.

• Contextual differences between treadmill and overground walking were identified as a potential barrier to generalization
• The study used a figure-8 overground walking path to study foot placement control outside the treadmill context
• The authors state these differences 'warrant caution in generalizing foot placement findings during treadmill walking to overground walking'

The differences in velocity feedback contribution during overground versus treadmill walking may be promising for the estimation of foot placement control in daily life gait.

• Exploratory analysis revealed the larger relative contribution of velocity feedback as a distinguishing feature of overground walking
• The authors suggest this finding 'might be promising for the estimation of foot placement control in daily life gait'
• This finding emerged from exploratory rather than confirmatory analyses