Date Published: February 2, 2017
Publisher: Public Library of Science
Author(s): Shu-Han Yu, Cheng-Ya Huang, Manabu Sakakibara.
In a postural-suprapostural task, appropriate prioritization is necessary to achieve task goals and maintain postural stability. A “posture-first” principle is typically favored by elderly people in order to secure stance stability, but this comes at the cost of reduced suprapostural performance. Using a postural-suprapostural task with a motor suprapostural goal, this study investigated differences between young and older adults in dual-task cost across varying task prioritization paradigms. Eighteen healthy young (mean age: 24.8 ± 5.2 years) and 18 older (mean age: 68.8 ± 3.7 years) adults executed a designated force-matching task from a stabilometer board using either a stabilometer stance (posture-focus strategy) or force-matching (supraposture-focus strategy) as the primary task. The dual-task effect (DTE: % change in dual-task condition; positive value: dual-task benefit, negative value: dual-task cost) of force-matching error and reaction time (RT), posture error, and approximate entropy (ApEn) of stabilometer movement were measured. When using the supraposture-focus strategy, young adults exhibited larger DTE values in each behavioral parameter than when using the posture-focus strategy. The older adults using the supraposture-focus strategy also attained larger DTE values for posture error, stabilometer movement ApEn, and force-matching error than when using the posture-focus strategy. These results suggest that the supraposture-focus strategy exerted an increased dual-task benefit for posture-motor dual-tasking in both healthy young and elderly adults. The present findings imply that the older adults should make use of the supraposture-focus strategy for fall prevention during dual-task execution.
Upright stance is a daily task that requires minimal attentional resources. A secondary task (suprapostural task) increases the demand on attentional resources especially in geriatric or neurologically impaired populations [1,2]. When undertaking a postural-suprapostural dual-task, one can prioritize either the postural or suprapostural task; each strategy results in different task outcomes and resource allocations. Young adults focusing on postural task often deteriorate automatic control of posture, resulting in increased postural instability, and postural stability increased when withdrawing attention from the postural task [3–6]. Aging causes degeneration of sensorimotor systems required for stance stability [7,8], and reduces attentional resource availability for undertaking dual-task conditions [1,9]. Therefore, older adults typically prioritize the postural task as a means of fall prevention [10–12]. It appears that under dual-task conditions without imposed task-prioritization, the unconscious “posture-first” strategy is an appropriate solution for the age-related postural destabilization occurring in older adults, as they are less able than young adults to reduce postural sway by adopting automatic postural control in the “supraposture-first” strategy [13–16].
Table 2 shows the baseline characteristics of subjects including the values of force-matching target, postural target and MMSE score. The young and older groups were similar in target force of the force-matching task and target angle of the postural task (p > 0.05). The MMSE score range was 25–30. For the older adult whose MMSE equal to 25 score, the years of education was eight years.
This study aimed to determine the relative contribution of task prioritization on DTEs between young and older adults in dual-task performance with a motor suprapostural goal. In instances where specific instruction were given for both the primary and secondary tasks, our results demonstrated that both postural and suprapostural performance benefited from an SF strategy in young and older adults. This suggests that SF is a better task prioritization strategy than PF for healthy adults, regardless of age.
In conclusion, SF strategy is the better movement strategy for both young and older adults during performance a motor suprapostural task while maintaining balance on an unstable surface. These findings of a potentially optimal task prioritization strategy may inform clinicians about the proper task prioritization instructions in fall prevention education or dual-task training. Because postural ability and attentional capacity might be more limited in patients with neurological diseases, such as stroke or Parkinson’s disease, compared to healthy older adults, future research should examine dual-task prioritization in neurologically impaired populations in order to develop more effective dual-task interventions.