Movement variability and limb loading symmetry during simulated daily functional tasks.

Movement variability describes an individual's capacity to repeatedly perform motor skills and provides better understanding of coordination during a task. The purpose of this research was to assess the impact that task type and sex assigned at birth have on movement variability and load symmetry in healthy younger adults. It was hypothesized that the between trial variability of peak impact force and average loading rate would not differ between sexes or between tasks (level walking, stair ascent, stair descent, and sit-to-stand) and that load symmetry would not differ between the four tasks for an individual participant using a level of significance of α = 0.05. Peak impact force (PIF) and average loading rate (ALR) were measured during level walking, stair ascent and descent, and sit-to-stand using loadsol® sensors collecting at 200 Hz (Novel Electronics, Pittsburg, PA, USA). Coefficients of variation (CV) and the Absolute Symmetry Index (ASI) were used to assess symmetry and movement variability. Between the 39 female and 33 male young adults that participated in this study, significant differences (p < 0.001) were observed between groups for mass, height, and limb length. PIF did not show an interaction between sex and task (p = 0.627) or between sexes (p = 0.685) but did show between-task differences (p < 0.001). The PIF ASI also showed a difference between tasks (p < 0.001). Tukey's post hoc testing showed that the PIF ASI differences between the sit-to-stand task and the other tasks were clinically meaningful (d > 0.8). The ALR did not show an interaction between sex and task (p = 0.069) or between sexes (p = 0.624) but did show between-task differences (p < 0.001). Tukey's showed that the ALR was different between tasks and was clinically meaningful (d > 0.8) except between level walking and stair ascent (p = 0.546). The ALR ASI showed a different between tasks (p < 0.001). Tukey's showed that the ALR ASI differences between tasks were all clinically meaningful (d > 0.8) except between level walking and stair ascent (p = 0.220).These findings suggest that the movement variability for all loading metrics that existed between tasks could be due to difference in motor control and the width of the base of support needed to complete the various tasks. For example, the joint coordination to complete a sit-to-stand task is different than what is needed during walking, stair ascent and stair descent. Understanding variability observed between daily tasks helps identify movement patterns that could be potential risk factors for injury.