Does dynamic stability govern propulsive force generation in human walking?

Michael G Browne,Jason R Franz

doi:10.1098/rsos.171673

Abstract

Before succumbing to slower speeds, older adults may walk with a diminished push-off to prioritize stability over mobility. However, direct evidence for trade-offs between push-off intensity and balance control in human walking, independent of changes in speed, has remained elusive. As a critical first step, we conducted two experiments to investigate: (i) the independent effects of walking speed and propulsive force (FP) generation on dynamic stability in young adults, and (ii) the extent to which young adults prioritize dynamic stability in selecting their preferred combination of walking speed and FP generation. Subjects walked on a force-measuring treadmill across a range of speeds as well as at constant speeds while modulating their FP according to a visual biofeedback paradigm based on real-time force measurements. In contrast to improvements when walking slower, walking with a diminished push-off worsened dynamic stability by up to 32%. Rather, we find that young adults adopt an FP at their preferred walking speed that maximizes dynamic stability. One implication of these findings is that the onset of a diminished push-off in old age may independently contribute to poorer balance control and precipitate slower walking speeds.

Highlights

Older adults are at a high risk of falls, and most of these falls occur during locomotor activities such as walking [1,2,3,4]
We present data from healthy young adult subjects that participated in two different but complementary experiments which we refer to as experiment 1 and experiment 2, both outlined in detailed below; 12 subjects participated in experiment 1 and 10 subjects participated in experiment 2
Biofeedback itself had only small discernible effects on our outcome measures; post hoc comparisons revealed that the use of biofeedback itself significantly increased only mediolateral sacrum position variability in both experiments and anterior–posterior sacrum position variability only in experiment 2 (p < 0.02)

Summary

Introduction

Older adults are at a high risk of falls, and most of these falls occur during locomotor activities such as walking [1,2,3,4]. Older adults may opt to walk slower to improve their resilience to unexpected balance challenges and mitigate their risk of falls. Prior to eliciting slower preferred speeds, advanced age is associated with a precipitous reduction in propulsive forces (i.e. the anterior component of the ground reaction force vector, FP) exerted during the pushoff phase of walking [7].

Methods

Results

Conclusion