Age-related differences in dynamic force control: pursuit tracking and compensatory tracking

Abstract

Objective: There are two major forms of visuomotor tracking compensatory and pursuit tracking The former tracking is to counter virtual perturbation in need of closed-loop control while the later entails to couple movement output to a moving target with a predictable trajectory Central processing of visual feedback have been proved to degenerate with aging that causes changes in structure of movement variability The age-related changes in force behaviors reflect a selective decline in the feedback and feedforward processes for force control with aging The purpose of the present study was to investigate the age-related differences in force fluctuation properties between the conditions of compensatory tracking and pursuit tracking Methods: 17 young health adults (23 0 ± 2 3) and 17 older health adults (68 4 ± 7 3) participated in the study All participants were required to exert a load-varying isometric force to couple 0 2 Hz sinusoidal target wave in the range of 9%–11% MVC of index abduction of right first dorsal interosseus in pursuit tracking The participants stabilized the target movement on the monitor at a constant level of 10% MVC by resisting sinusoidal virtual perturbation during compensatory tracking Normalized changes in force behaviors and force fluctuation properties between compensatory tracking and pursuit tracking for the two populations were contrasted Results: The results of the study indicated that normalized difference in force fluctuations of the older adults was significantly greater than that of the young adults In addition the normalized difference in SampEn of the older adults was significantly greater than that of the young adults Other force fluctuation properties in ratio of residual power task error correlation between the target and force trajectory and peak amplitude did not significantly differ with the older and the young adults Conclusions: In summary older adults had more force variability in visuomotor tasks by virtue of the differential age effect on force characteristics for the two tracking patterns The greater normalized change in the size of force fluctuations for the elderly indicated the elderly were more variable in force control than young adults when tracking task shifts from pursuit modes to compensatory mode In addition the less normalized change in the complexity of force fluctuations for the aged symbolized the aged exhibited a more regular force fluctuations than the young when tracking task shifts from compensatory modes to pursuit modes Thus the provision of feedback-based visuomotor practice to the elderly should be aware of the fact that degenerative changes in feedback control could destabilize force output with less strategic richness for a visuomotor task

Date of Award	2017 Aug 29
Original language	English
Supervisor	Ing-Shiou Hwang (Supervisor)