Effects of smartphone use while walking on external knee abduction moment peak: A crossover randomized trial on an instrumented treadmill

Introduction: In addition to its effects on cognitive awareness, smartphone use while walking may reduce the speed, regularity, and symmetry of walking. Although its effects on spatiotemporal gait parameters, such as walking speed and step width, have already been studied, little is currently known about the impact of smartphone dual tasking on lower limb kinetics.Research question: Does smartphone use during walking alter gait patterns (i.e., walking speed and step width) and consequently external knee moments?Methods: In a four-period crossover trial, external knee moment peaks, walking speed, and step width were assessed in 27 healthy adults during matched-speed walking, self-paced walking, selfpaced walking with spoken calculation tasks, and self-paced walking with smartphone-entered calculation tasks. Differences between the smartphone use condition and all other conditions were determined using repeated measures ANOVA with predefined contrasts.Results: Decreased walking speed and increased step width were observed during smartphone use. The mean external knee abduction moment peak (Nm/kg) differed significantly (p < 0.01) across the intervention condition, namely walking with smartphone-entered calculations (0.15; 95 % CI: 0.12, 0.18), and the control conditions, namely matched-speed walking (0.11; 95 % CI: 0.08, 0.13), self-paced walking (0.11; 95 % CI: 0.09, 0.14), and walking with spoken calculations (0.14; 95 % CI: 0.12, 0.16). After confounder adjustment for walking speed, step width, gender, and age, this primary outcome was significantly different between using the smartphone and self-paced walking (p < 0.01, r = 0.51). This effect size was reduced when comparing smartphone use with spoken calculations (p = 0.04, r = 0.32).Conclusion: When using a smartphone while walking, walking speed is slowed down, step width is increased, and knee moments are adversely altered compared to walking without dual tasking. These altered knee moments are partially, but not entirely, attributable to the cognitive calculation task. These effects are age-independent, but women are more affected than men. Nevertheless, it remains unclear whether sustained walking while using a smartphone adversely affects the development of knee joint pathologies.