Gait ratios and variability indices to quantify the effect of using smartphones in dual-task walking

Smartphone use is one of the most common activities performed while walking: recent studies showed how this behaviour affected spatio-temporal, smoothness, symmetry and regularity gait parameters. In this study, we investigated a subset of additional gait parameters, potentially indicative of gait instability, to check whether concurrent smartphone activities cause deviations from stable walking. Ten young healthy adults were asked to walk outdoor normally and while performing five smartphone-based dual-task activities, with different levels of cognitive effort. Three groups of gait parameters, extracted by a single waist-mounted tri-axial inertial sensor, were analyzed: Gait Ratios group included Stride-to-Stance Time Ratio (SSTR)—equal to the golden ratio$$ \upvarphi $$ ≈ 1.618 in normal walking—and Walk Ratio (WR)—the ratio between Step Length (SL) and cadence, roughly constant within healthy subjects—Variability Measures group included Coefficients of Variation (CV) of SL and step time; Acceleration Ratios group composed of Root Mean Squared acceleration Ratios (RMSR)—the ratio between rms along a single direction and the total rms acceleration. When a dual-task is present, SSTR did not show significant variations from Baseline. A continuous typing activity with low cognitive engagement caused a significant decrease of WR with respect to all the other tasks. RMSR in the mediolateral direction and the CV SL showed visible yet not significant proportion with the amount of experienced cognitive effort. The resulting alterations were in general inconclusive as to their possible link with a reduced ability to adapt the locomotion structure to the context changes, even if for some parameters the observed proportion with cognitive effort and visual domain may need to be deepened on a bigger sample size, possibly including more challenging dual-task demands.