Kinematic and neuromuscular characterization of cognitive involvement in gait control in healthy young adults

The signature of cognitive involvement in gait control has rarely been
studied using both kinematic and neuromuscular features. The present study
aimed to address this gap. Twenty-four healthy young adults walked on an
instrumented treadmill in a virtual environment under two optic flow
conditions: normal (NOF) and perturbed (POF, continuous mediolateral
pseudorandom oscillations). Each condition was performed under single-task
and dual-task conditions of increasing difficulty (1-, 2-, 3-back).
Subjective mental workload (raw NASA-TLX), cognitive performance (mean
reaction time and d-prime), kinematic (steadiness, variability and
complexity in the mediolateral and anteroposterior directions) and
neuromuscular (duration and variability of motor primitives) control of
gait were assessed. The cognitive performance and the number and
composition of motor modules were unaffected by simultaneous walking,
regardless of the optic flow condition. Kinematic and neuromuscular
variability was greater under POF compared to NOF conditions. Young adults
sought to counteract POF by rapidly correcting task-relevant gait
fluctuations. The depletion of cognitive resources through dual-tasking
led to reduced kinematic and neuromuscular variability and this occurred
to the same extent regardless of simultaneous working memory (WM) load.
Increasing WM load led to a prioritization of gait control in the
mediolateral direction over the anteroposterior direction. The impact of
POF on kinematic variability (step velocity) was reduced when a cognitive
task was performed simultaneously, but this phenomenon was no modulated by
WM load. Collectively, these results shed important light on how young
adults adjust the processes involved in goal-directed locomotion when
exposed to varying levels of task and environmental constraints.