Improving posture-motor dual-task with a supraposture-focus strategy in young and elderly adults

RESEARCH ARTICLE Improving posture-motor dual-task with a supraposture-focus strategy in young and elderly adults Shu-Han Yu1, Cheng-Ya Huang1,2* 1 Physical Therapy Center, National Taiwan University Hospital, Taipei City, Taiwan, 2 School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Taipei City, Taiwan * a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Yu S-H, Huang C-Y (2017) Improving posture-motor dual-task with a supraposture-focus strategy in young and elderly adults. PLoS ONE 12 (2): e0170687. doi:10.1371/journal.pone.0170687 Editor: Manabu Sakakibara, Tokai University, JAPAN Received: October 25, 2016 Accepted: January 9, 2017 Published: February 2, 2017 Copyright: © 2017 Yu, Huang. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This research was supported by a grant from the Ministry of Science and Technology, R.O. C. Taiwan, under grant no. MOST 103-2314-B002-007-MY3. Competing Interests: The authors have declared that no competing interests exist. Abstract 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 posturemotor 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. Introduction 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 dualtask, 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 PLOS ONE | DOI:10.1371/journal.pone.0170687 February 2, 2017 1 / 16 Task priority of dual-task in the elderly 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]. However, regarding to impose task prioritization in a postural-suprapostural task, the optimal postural strategy for older adults is still an issue of debate. A few studies have reported a decrease in postural stability when older people performed a postural-suprapostural task with paying attention to the suprapostural tasks [17,18], whereas other studies have shown enhanced postural stability when more attention was directed to the suprapostural task [19,20]. In fact, the dual-task cost increased proportionally with the task compatibility of two concurrent tasks, especially in older adults [21,22] who showed a larger performance decrement in posture-motor dual-tasking than posture-cognition dual-tasking [23]. Moreover, variations in task prioritization effect could be ascribed to the nature of the instructions given in the experiment [18,24] as the instruction format was found to influence relative resource allocation between the two tasks. Verbal instruction affects the degree of attention being devoted to the secondary task. In the extreme case, subjects may abort the suprapostural task for the sake of the postural task. In light of this inconsistency in findings of a task prioritization effect on postural control in older adults, the purpose of this study was to reexamine the influence of task prioritization (posture-focus (PF) versus supraposture-focus (SF)) in both young and older adults who were given specific task-priority instructions to maintain postural balance while performing a motor suprapostural task simultaneously. In the present study, a precision grip task was used as the motor suprapostural task. Besides fine force control, a precision grip task required cognitive aspects of motor control such as response to an executive signal as fast as possible and sensorimotor integration during movement preparation period [25,26]. With this complex posture-motor-cognitive task, sophisticated allocation of attentional resources is needed by intensive resource competition between the postural and suprapostural tasks and/or by simultaneously coordinating the two tasks, pertaining to the relative importance of resource allocation between the postural and suprapostural tasks when task prioritization varies. Our main hypotheses were that (1) postural and motor performance of a postural-suprapostural task would be differently affected by the strategy of task prioritization and (2) the effects of task prioritization would be differ (...truncated)