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Background: Individuals with Parkinson’s disease (PD) with freezing of gait (FoG) exhibit difficulty with changes in sensory input, indicating a potential sensorimotor integration deficit. Understanding how levodopa impacts balance particularly in FoG, is critical. As traditional postural sway measures may not fully capture the complexity of balance control, rambling and trembling decomposition of the center of pressure allows a more detailed assessment of postural control by distinguishing between supraspinal and spinal contributions, offering insights into sensorimotor integration deficits. This study aims to analyze the effects of medication and FoG on rambling and trembling in quiet standing in individuals with PD. Methods: We analyzed 13 individuals with PD with FoG (PD freezers) and 19 individuals with PD without FoG (PD nonfreezers) while quiet standing on a rigid and malleable surface under (ON) and without (OFF) dopaminergic medication. Area, root mean square, and mean velocity were calculated for rambling and trembling trajectory. Results: For the rambling, all variables were significantly higher on the malleable compared with the rigid surface. For trembling, (a) all variables were higher on the malleable compared with the rigid surface (p < .001), and (b) area and medial–lateral root mean square were significantly higher ON compared with OFF medication for both groups of participants similarly. Conclusion: Our results strengthen the evidence that PD freezers have the same postural sway in quiet posture as PD nonfreezers, using similar mechanisms to control the posture. In addition, levodopa influences spinal mechanisms more than supraspinal ones in individuals with PD in quiet standing.

Task difficulty is a major factor that affects postural control and stability. However, there is little information about the effects of task difficulty on postural control during gait termination in combination with a manual task. The present study investigated postural control during combined gait termination and a manual task with different levels of manual task difficulty. Right-handed, healthy young adults (n = 15) performed five trials of combined gait termination with a manual fitting task for each of four different manual task conditions, varying target size (large and small) and distance (short and long). Average time-to-contact of the center of pressure and upper body (sternum) was assessed in three separate phases of the combined task: preparation, reaching, and stabilization phases. Longer reaching distance reduced time-to-contact not only in the reaching phase but also in both the preparation and stabilization phases. However, there were no effects of target size on time-to-contact. These results indicate that increasing manual task demands requires integration throughout gait termination and can impact postural stabilization after task completion even in young healthy adults.

Background: Increased sway within a stationary base of support (BoS) is often interpreted as worse postural control. However, larger persons may have larger feet, facilitating broader sway patterns within their wider/longer base. Time to boundary (TtB) incorporates foot placement dimensions into the calculation and, thus, may not be confounded by dissimilar anthropometric features. Methods: Ninety-seven healthy adults stood quietly on a force platform for 150 s with their feet together while barefoot. BoS characteristics, center of pressure motion, and TtB were calculated and correlated with body height for eyes open and closed conditions. Results: BoS width, length, and total area positively correlated with body height. Path length and sway area were positively correlated with height for both vision conditions, with stronger correlations observed with eyes closed. At the same time, TtB was not correlated with height in either visual condition. Consequently, the tallest 20 individuals in the sample displayed greater path length and sway areas but equal TtB as the shortest 20 persons. Conclusion: Observed differences in position-based center of pressure measures could be an artifact of body size inequality not postural (in)stability. Meanwhile, TtB is normalized to BoS and is, therefore, not confounded by anthropometric differences.