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APPLIED SCIENCES

Dual-Task Walking Capacity Mediates Tai Ji Quan Impact on Physical and Cognitive Function

LI, FUZHONG1; HARMER, PETER2; CHOU, LI-SHAN3

Author Information
Medicine & Science in Sports & Exercise: November 2019 - Volume 51 - Issue 11 - p 2318-2324
doi: 10.1249/MSS.0000000000002051

Abstract

With the rapidly growing aging population worldwide, the quality of life and functional mobility of older adults are increasingly important from the perspectives of public health and preventative health care of geriatric diseases. Advancing age is associated with declines and impairments in physical and cognitive capacities (1–4), and deterioration in these functional abilities poses major challenges to older adults, especially in activities that require dual-task capacity (e.g., walking while talking or counting coins for the fare while stepping onto a bus) (5,6), with evidence showing increased variability in gait speed (7), reduced dual-task ability (8,9), and elevated risk for dementia (10) and falls (11).

There is increasing evidence supporting the health benefits of regular physical and mental exercise (12,13), either standalone (physical) or in combination (dual-task intervention), to improve cognition (14–18) and dual-task performance (19–21) in old age. However, there is a significant knowledge gap with respect to whether exercise-induced gains in dual-task capacity can serve as the mechanism(s) linking to improved mobility, balance, and cognitive function, as well as reduced falls, all of which are outcomes of high clinical relevance and functional importance in maintaining independence and quality of life (2,22). Filling this knowledge gap is important for developing tailored dual-task-enhancing exercises that can directly ameliorate disabilities and improve life independence among older adults who are at risk for impaired cognitive function, reduced mobility, and falls.

Evidence indicates that both multimodal and Tai Ji Quan exercises improve cognition in older adults (14–18). Multimodal interventions commonly consist of different types of physical exercises (i.e., aerobic, strength, flexibility, balance) that are configured to impose cognitive demands (23) and have been shown to improve cognition (14–16,18) including dual task ability (16). Tai Ji Quan (24) provides an alternative exercise regimen that involves learning and practicing a set of mind- and goal-directed, deliberate, choreographed spiraling movements, features that are inherently multitasking with high demands on attentional resources (17,25) and that have been shown to reduce dual task gait variability, offering a potential mediator of fall risk in older adults (26).

On the basis of the evidence that exercise training improves physical/mental and dual-task gait outcomes (15–17,19–21) and that dual-task exercise interventions, including integrated exercise-cognitive training, improve physical performance (16,17), enhance balance confidence during daily activities (27), and reduce fall risk (28), the purpose of this study was to test an unexplored mediational hypothesis: that Tai Ji Quan and multimodal exercise interventions, compared with stretching (control) exercise, will improve physical performance, activity confidence, and global cognitive function, and reduce falls through exercise-induced change in dual-task gait performance in older adults at high risk of falling. Given the intertwined motor-cognitive nature of Tai Ji Quan, we predict that, compared with multimodal exercise, the mediational effects would be most pronounced by Tai Ji Quan.

METHODS

Study Design and Participants

This study involved a secondary analysis of a randomized clinical trial that was registered at ClincialTrials.gov (NCT02287740) and took place from February 2015 to September 2018. The study protocol was approved by the Institutional Review Board of the Oregon Research Institute. The participants received verbal and written information about the study and its procedures and provided written consent to participation. The original trial, which followed the Consolidated Standards of Reporting Trials reporting guidelines, was designed to examine the effect of exercise on reducing incidence of falls, with details of trial design and methodologies presented elsewhere (29). In brief, the randomized clinical trial compared Tai Ji Quan: Moving for Better Balance (TJQMBB; n = 224) and multimodal exercise (n = 223) to stretching exercise (n = 223) on incidence of falls and injurious falls (29,30).

The study participants (N = 670, mean age = 77.7, men = 234; women = 436) were community-dwelling older adults 70 yr or older who were identified as being at high risk of falling, which was operationalized as individuals who fell at least once in the preceding 12 months (with a medical referral indicating that the participant was at risk of falls) or a performance score of greater than 13.5 s on Timed Up & Go) (31). The entire study was divided into two phases: 6 months of structured in-class exercise and a 6-month (nonintervention) follow-up. Upon agreeing to participate, the participants were randomized into one of the three active intervention groups described previously. The study assessors were blinded to group allocation during the data collection period whereas the participants were aware of their group assignment.

Intervention

The three active interventions were implemented twice weekly for 24 wks, with a total of 48 class sessions of 60 min in duration scheduled for each arm (29). Participants assigned to the TJQMBB group received training on Tai Ji Quan forms mixed with variations and therapeutic movement exercises derived from Tai Ji Quan (32). The training protocol focused attention on bilateral weight shifting, excursion of the center of mass around the participants’ limits of stability, and integrated breathing in unison with the Tai Ji Quan movement execution. Participants assigned to the multimodal exercise group received training that combined aerobics (e.g., walking), balance (e.g., heel-toe and line walking, single-leg standing, standing on balance foams), strength (e.g., with and without equipment [tubing, dumbbells]), and flexibility (stretching) exercises (33). The training protocol primarily emphasized repetitive movements of various exercises (e.g., stepping, lunging, standing). Finally, serving as an exercise control, participants allocated to the stretching group received exercises that consisted of breathing, stretching, and relaxation activities, with most of the exercise activities performed in a seated position.

Measures

Distal outcomes

These measures, ascertained at 12 months, included Short Physical Performance Battery (SPPB) (34), Activities-Specific Balance Confidence (ABC) (35), Montreal Cognitive Assessment (MoCA) (36), and falls (29). Details of each are described below.

The SPPB measures gait speed (4 m), repeated chair stand (five times), and ability to stand for 10 s with feet in three different positions (feet together, semi tandem, tandem). The total scores from these sub-measures range from 0 (worst performance) to 12 (best performance), with higher scores indicating better lower-extremity function. The ABC contains a 16-item self-report measure that assesses an individual’s confidence in performing daily activities without losing balance, with items rated on a 0 (no confidence) to 100 (complete confidence) scale. The overall score was calculated by adding item scores and then dividing by the total number of items with higher scores indicating higher activity confidence. Montreal Cognitive Assessment was measured by a 30-item scale that assesses global cognitive function involving the domains of memory recall, visuospatial abilities, executive functions, attention, language, and orientation to time and place. The scores range from 0 to 30, with higher scores indicating better global cognitive function.

The number of falls during the entire 12-month study was recorded via a self-reported monthly falls calendar, which recorded the number of falls in the past month. This information was collected from the date of the first intervention class and continued until 12 months later, or until a participant withdrew, died, or was lost to follow-up. As a distal outcome for this study, the number of falls reported in this study was summed, as a count variable, from the end of the 6-month active intervention to the end of the 12-month follow-up.

Mediator

The Instrumented Timed Up & Go (iTUG, APDM, Inc) was used to assess gait performance. Before the iTUG test trial, participants were instructed to stand up, from a chair, walk a 14-m walkway at normal pace (7 m toward a line, turn, and 7 m toward the chair), and turn around and sit down on the chair (37). The iTUG test was administered with two walk formats: first without a cognitive task (i.e., single physical walk; two trials) and then with an added verbalized serial subtraction cognitive task (i.e., counting numbers backward by 5 starting with the number 95 in trial 1 and number 65 in trial 2). Within dual-task trials, serial subtractions of 5 were not performed at random, and no specific instructions were given regarding task prioritization.

For the purpose of this study, the total walking duration (measured in seconds) during the 14-m walk, at normal pace, was recorded. Using the average score (in seconds) of each walk, a dual-task cost measure was estimated using the following formula:

Scores derived from formula 3 above were used to define the intervention mediator for which positive values indicate deteriorated performance in dual task (i.e., dual-task cost), whereas negative values represent an improvement in dual-task performance with respect to single-task (i.e., dual-task benefit).

Covariates

These included participants’ age, sex, and number of falls 6 months before intervention. In controlling for the effect of intervention and physical activity during follow-up, SPPB, ABC, and MoCA scores at 6 months (intervention termination) and levels of moderate-vigorous physical activity (in minutes per week), measured by the International Physical Activity Questionnaire (38), during follow-up (ascertained at 12 months), as well as length of follow-up, were included.

Data Analysis

At the 12-month follow-up, full data on SPPB, ABC, and MoCA measures were available on 566 participants (TJQMBB, 188; multimodal, 191; stretching, 187), representing a 16% loss at follow-up. A total of 634 (95%) participants provided full follow-up data on falls. Data on iTUG at 6 months were available on 633 (94%) participants (TJQMBB, 211; multimodal, 211; stretching, 211).

Statistical analyses were performed using the Mplus software (version. 8.2; Muthén & Muthén, Los Anglos, CA). We first examined between-group differences on the distal and mediating variables. Differences among the three intervention groups were examined by testing the differences between a constrained model (in which the parameter of interest was constrained to be equivalent across the two comparison groups) and a nonconstrained model (in which the parameter was allowed to vary across the groups). The null hypothesis (i.e., equal value) was rejected if the Wald test was significant. Analyses were conducted with intention-to-treat. Missing data for SPPB, ABC, and MoCA scores were imputed via a maximum likelihood approach. Falls data were the total number of falls for each participant reported during follow-up adjusting for follow-up times.

We tested the hypothesized meditational effect of change in dual-task cost on lower-extremity physical performance, activity confidence, and incidence of falls through a moderated intervention mediation approach (39). A schematic model of the mediational effect of intervention on the distal outcomes is displayed in Figure 1, where mediation of the distal outcomes is defined by change in dual-task cost (mediator) as moderated by intervention (dummy coded with 1 = TJQMBB/multimodal exercise, 0 = stretching exercise) controlling for covariates. With this approach, the mediating effect of dual-task cost on lower-extremity physical performance, activity confidence, and incidence of falls was moderated by the a priori specified intervention conditions (i.e., TJQMBB or multimodal exercise with a cross-product of intervention by change in dual-tasking cost) controlling for outcome-specific covariates (including age, sex, SPPB, ABC, MoCA, falls outcomes at 6 months, levels of physical activity during follow-up, and length of study follow-up). Within the path analysis framework, the indirect effect can be calculated as (β1 + β3 × Intervention_TJQMBB/Multimodal) × γ1 × (Intervention_TJQMBB/Multimodal − Intervention_Stretching). Unstandardized structural equation coefficients (B) along with 95% confidence intervals (95% CI) are reported. The level of statistical significance was set at P < 0.05 for all computations.

FIGURE 1
FIGURE 1:
A schematic model of the hypothesized mediational effect of intervention on study distal outcomes.

RESULTS

Baseline characteristics of the study participants were similar in the three randomized exercise interventions. There were no between-group differences in intervention adherence (77%) with an overall attrition rate of 13% over the 6-month intervention (29). No adverse effect related to the intervention or the assessment was reported. There were differences between 6 and 12 months in the outcome and mediator variables across intervention groups (see Table, Supplemental Digital Content 1, Between-group differences between 6 and 12 months in the study outcome and mediator variables, http://links.lww.com/MSS/B637).

Descriptive statistics of the distal outcomes and the mediator are shown in Table 1. Tests of between-groups showed a statistically significant difference between TJQMBB and stretching exercise in the variables of SPPB, ABC, MoCA, falls at 12 months, and the mediating variable of change in dual-task cost, with the scores in favor of TJQMBB. Compared with stretching exercise, multimodal exercise exhibited an improvement on SPPB, ABC, and MoCA and a reduction in falls, but showed no difference in dual-task cost (P = 0.11). Although TJQMBB significantly lowered dual-task cost (P = 0.009) relative to multimodal exercise, the two exercise interventions did not differ on other outcomes.

TABLE 1
TABLE 1:
Descriptive statistics of the study outcomes.

Estimates from the tests of mediation of intervention, including both direct and indirect effects, are presented in Table 2, with the results summarized below.

TABLE 2
TABLE 2:
Model estimates predicting change in the study outcomes.

SPPB

There was a significant TJQMBB intervention–mediator interaction effect (P = 0.008), indicating that reduced dual-task cost resulting from the 6-month intervention significantly improved lower-extremity function at 12 months among TJQMBB participants relative to those in the stretching group (B = 0.02, 95% CI, 0.01–0.07). Furthermore, the indirect effect of intervention (B = −0.10, 95% CI, −0.21 to −0.03) through change (in a reduced direction) in dual-task cost to SPPB was significant (P = 0.04). The intervention–mediator interaction effect, however, was not significant (P = 0.94) for multimodal exercise, which showed a significant direct effect of intervention on improving lower-extremity functioning (B = 0.36; 95% CI, 0.03–0.61; P = 0.02).

Activities-specific Balance Confidence

There was no significant TJQMBB intervention–mediator interaction effect (P = 0.12). However, there was a significant indirect effect of intervention, through the mediation of change in dual-task cost (B = −0.59, 95% CI, −1.26 to −0.15; P = 0.03). Multimodal exercise showed a significant direct effect of intervention on improved perceptions of activity confidence (B = 2.39; 95% CI, 0.32–4.63; P = 0.03) but a marginal effect on the dual-task cost (P = 0.05). The intervention showed no mediational effect of change in dual-task cost on the ABC scores (P = 0.83).

Montreal Cognitive Assessment

There was a significant TJQMBB intervention–mediator interaction effect (P = 0.03), indicating that reduced dual-task cost improved global cognitive function during follow-up among TJQMBB participants relative to those in the stretching group (B = 0.04; 95% CI, 0.007–0.08). The direct effect of intervention on MoCA was not significant (P = 0.7), but there was a significant indirect effect (B = −0.09; 95% CI, −0.21 to −0.02, P < 0.05). Multimodal exercise showed no significant direct effect of intervention on cognitive function (B = 0.56; 95% CI, −0.005 to 1.05) or on the dual-task cost (P = 0.06). The intervention showed no mediational effect of change in dual-task cost on the MoCA scores (P = 0.44).

Falls

There was a significant TJQMBB intervention by mediator intervention effect (P < 0.001), indicating that reduced dual-task cost significantly lowered the incidence of falls during follow-up among TJQMBB participants relative to those in the stretching group (B = −0.05; 95% CI, −0.07 to −0.02). Although the mediational effect was significant, the indirect effect was not (P = 0.7), indicating that some of the significant mediation was reduced due to the significant direct effect of intervention on falls (B = −0.64, 95% CI, −1.04 to −0.29, P = 0.001). For multimodal exercise, the results showed no indication of the mediational effect of dual-task cost on the outcome (P = 0.61). Multimodal exercise, however, had a significant effect on lowering the dual-task cost (B = 2.08; 95% CI, 0.15–4.09) and a direct effect on reducing falls (B = −0.55; 95% CI, −0.91 to −0.26) during follow-up.

DISCUSSION

In this comparison study of two different types of exercise interventions with stretching exercise, we found support for our hypothesis that improvement in dual-task physical-cognitive performance as a result of a 6-month Tai Ji Quan training intervention mediated improvements at follow-up in the measures of physical performance, activity confidence, global cognitive function, and falls among older adults at high risk of falling. The hypothesized mediational effect was not supported for multimodal exercise. However, the multicomponent exercise modality had a direct effect on follow-up measures of physical performance, activity confidence, and falls.

To the best of the authors’ knowledge, this is the first study to examine the association between intervention-induced dual-task capability and subsequent improvements in outcomes of physical performance, confidence of performing daily activities, cognitive function, and falls. Previous exercise intervention studies showed that improvements in lower-body strength resulting from resistance training mediated the significant effect of strength training on cognitive function in older adults with mild cognitive impairment (40) and in healthy older adults (41). The current study provides novel data on the potential role of Tai Ji Quan training-induced change in dual-tasking capability to positively impact physical performance, activity confidence, cognitive function, and falls in older adults at high risk of falling.

Performance of Tai Ji Quan involves physical and cognitive responses to concurrent task demands for motor control of postural stability and focused attention to visual and auditory instructional cueing during learning and practicing (32,42). Therefore, its practice involves engagement of multiple cognitive domains that has potential to mediate the relationship between Tai Ji Quan and physical and cognitive function. Despite these inherent features, Tai Ji Quan has mainly been conceived as a physical/calisthenic-like activity and has been operationalized as such in practice (42). Findings from the current study on the mediation by physical-cognitive ability performance, however, suggest opportunities to capitalize on the multitasking nature of Tai Ji Quan for optimizing future interventions. This involves efforts to tailor Tai Ji Quan toward cognition stimulation that explicitly integrates motor-sensory-cognitive activities into a single, treatment-specific, cognitively engaging intervention with the ultimate goal of improving cognitive function, balance, and physical performance, and reducing falls among older adults at higher risk for cognitive decline (e.g., people with mild cognitive impairment).

In contrast to the mediational effects observed for Tai Ji Quan, for multimodal exercise we found no significant improvement in dual-task capability relative to stretching exercise or mediational influence of change in dual-task capacity on the study outcomes. We also observed no prospective intervention effect on global cognitive function. The lack of the mediating and cognitive effects in this exercise modality may be due in part to the explicit emphasis on engaging in repetitive, automated, mechanical exercise movements that may not be of sufficient stimulation to tax older adults’ attentional resources. Although evidence supports the cognitive benefits of multimodal exercise interventions (41,43), as well as combined exercise with cognitive training (44,45), the effects on dual-task capability from controlled and uncontrolled studies are less clear and have conflicting findings (46–49). Thus, the extent to which multimodal exercise improves dual-task performances and whether the gains can translate into improved physical and cognitive performance warrant further investigation.

The strengths of the present study include its rigorous trial design and well-defined and appropriately powered study outcomes that targeted a population of older adults at high risk of falling (29). Nevertheless, the study has limitations that future studies can address. First, the data analyzed were from a trial that was not specifically powered for detecting the mediational mechanism of the intervention on the distal clinical outcomes investigated. Nevertheless, these results provided compelling preliminary data for designing, optimizing, and powering future mechanistic trials. Second, the study used counting numbers backwards as the cognitive component of a dual-task performance. Future studies could further tap into the cognitive reserve or dual-task capacity by using performance measures that resemble real-world scenarios, such as negotiating physical hurdles on foot while making mathematical calculations. Third, though we used two starting numbers (i.e., 95, 65) for the iTUG during the dual-task test, we did not use a randomized number (e.g., serial subtractions of 5 from a random number) or vary the subtraction number (e.g., −7 or − 3). Therefore, it is possible that our approach may have led to a possible bias in terms of gait behavior and learning effect.

In conclusion, both Tai Ji Quan and multimodal exercise improved physical performance and perceived daily activity confidence, and reduced the number of falls. Tai Ji Quan, however, effectively enhanced dual-task walking capability, which in turn led to improved physical performance, activity confidence, and global cognitive function, and a reduced incidence of falls in older adults at high risk of falling. Findings from this study provide impetus for developing more effective and tailored Tai Ji Quan cognitive interventions targeting community-dwelling older adults at high risk for physical and cognitive declines and concomitant challenges in performing daily activities.

Competing interests: Li reports a grant from National Institutes of Health during the conduct of the study and being the founder and owner of Exercise Alternatives, LLC, a consulting company to which a voluntary licensing fee for Tai Ji Quan: Moving for Better Balance is paid. No other disclosures were reported.

All authors contributed the planning, drafting and approval of this article.

This work was supported by grant AG045094 from the National Institute on Aging. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by ACSM.

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Keywords:

COGNITION; EXERCISE; DISABILITY; QUALITY OF LIFE

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