Minimum toe clearance: probing the neural control of locomotion

Tim Killeen,Björn Zörner,Lilla Lőrincz,László Demkó,Michael Linnebank,Marc Bolliger,Armin Curt,Christopher S Easthope,Linard Filli

doi:10.1038/s41598-017-02189-y

Abstract

Minimum toe clearance (MTC) occurs during a highly dynamic phase of the gait cycle and is associated with the highest risk of unintentional contact with obstacles or the ground. Age, cognitive function, attention and visual feedback affect foot clearance but how these factors interact to influence MTC control is not fully understood. We measured MTC in 121 healthy individuals aged 20–80 under four treadmill walking conditions; normal walking, lower visual field restriction and two Stroop colour/word naming tasks of two difficulty levels. Competition for cognitive and attentional resources from the Stroop task resulted in significantly lower mean MTC in older adults, with the difficult Stroop task associated with a higher frequency of extremely low MTC values and subsequently an increased modelled probability of tripping in this group. While older adults responded to visual restriction by markedly skewing MTC distributions towards higher values, this condition was also associated with frequent, extremely low MTC values. We reveal task-specific, age-dependent patterns of MTC control in healthy adults. Age-related differences are most pronounced during heavy, distracting cognitive load. Analysis of critically-low MTC values during dual-task walking may have utility in the evaluation of locomotor control and fall risk in older adults and patients with motor control deficits.

Highlights

Falls from standing height in adults over the age of 60 are associated with 1-year mortality as high as 33% and lead to considerable morbidity, reduced independence and financial burdens[1, 2]
We developed a paradigm to investigate the effect of cognitive load and attention on the control of Minimum toe clearance (MTC) in healthy adults of all ages
We demonstrate that a combined analysis of the response of MTC to different locomotor conditions, including distribution analysis, is feasible and capable of revealing age-dependent and task-specific differences in motor control mechanisms in a large cohort of healthy adults

Summary

Introduction

Falls from standing height in adults over the age of 60 are associated with 1-year mortality as high as 33% and lead to considerable morbidity, reduced independence and financial burdens[1, 2]. Cognitively demanding, walking with restricted vision appears to be associated with minimal gait adaptations in healthy older adults[27] and with a slightly increased mean MTC relative to normal walking[28,29,30]. Relying solely on changes in MTC mean/median or variability values to understand tripping risk and/or locomotor control under challenging walking conditions implicitly assumes normal distribution of MTC values. This is rarely the case in groups or individuals[22, 29, 31] and task-related shifts in frequency distribution may significantly increase an individual’s tripping risk. We hypothesise that condition effects on MTC will be most pronounced in the group of adults aged over 60 and that the characteristics of MTC frequency distributions will result in higher modelled tripping risk in this group

Methods

Results

Conclusion