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THE EFFECTS OF DUAL-TASK TRAINING ON COGNITIVE AND PHYSICAL FUNCTIONS IN OLDER ADULTS WITH COGNITIVE IMPAIRMENT; A SYSTEMATIC REVIEW AND META-ANALYSIS

 

N. Ali1,2, H. Tian1,3, L. Thabane4,5, J. Ma4, H. Wu6, Q. Zhong6, Y. Gao7, C. Sun6, Y. Zhu8, T. Wang8

 

1. First School of Clinical Medicine, Nanjing Medical University, Nanjing, Jiangsu, China; 2. Swat Institute of Rehabilitation & Medical Sciences, Swat, Khayber Pakhtoonkhwa, Pakistan; 3. School of Rehabilitation Medicine, Nanjing Medical University, Nanjing, China; 4. Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada; 5. Biostatistics Unit, St Joseph’s Healthcare, Hamilton, Ontario, Canada; 6. Rehabilitation Department, Nanjing Drum Tower Hospital Clinical College of Nanjing Medical University, Nanjing, Jiangsu, China; 7. Rehabilitation Department, The Affiliated Suzhou Hospital of Nanjing Medical University, Suzhou Municipal Hospital, Gusu School, Nanjing Medical University, Suzhou, Jiangsu, China; 8. Department of Rehabilitation Medicine, First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China. N. Ali and H. Tian have contributed equally.

Corresponding Author: Tong Wang, Department of Rehabilitation Medicine, The First Affiliated Hospital of Nanjing Medical University, No. 300 of Guangzhou Road, Nanjing, Jiangsu 210029, China. Tel: +86 13951680478, fax: +862583318752. E-mail: wangtong60621@163.com; Yi Zhu, Department of Rehabilitation Medicine, The First Affiliated Hospital of Nanjing Medical University, No. 300 of Guangzhou Road, Nanjing, Jiangsu 210029, China. Tel: +86 13705164030, fax: +862583318752. E-mail: lucky.zyx@163.com

J Prev Alz Dis 2022;
Published online January 20, 2022, http://dx.doi.org/10.14283/jpad.2022.16

 


Abstract

Background and objective: Individuals with Alzheimer disease and dementia experience cognitive decline and reduction in physical capabilities. Engaging in cognitive challenges and physical exercises is effective in reducing age-related cognitive and physical decline. It is believed that physical activity in the context of cognitive challenges might enhance the process of neurogenesis in the adult brain, but how effective are such interventions? Is there enough evidence to support that dual-task training is more effective than cognitive or physical training alone? To what extent can such training improve cognitive and physical functions in patients at various stages of cognitive decline?
Methodology: This systematic review with meta-analysis summarizes the emerging evidence of dual-task training for enhancing cognitive and physical functions in older individuals with cognitive impairment, dementia or Alzheimer’s disease. A systematic search was carried out in MEDLINE, PubMed, EMBASE, and Cochrane Library with the following search terms: randomized control trials, dual-task training, SCD, MCI, dementia, and Alzheimer’s disease.
Results: A total of 21 studies with 2,221 participants were identified. The results of dual-task tanning intervention are summarized as change in global cognitive function; SMD = 0.24, (P= 0.002), memory; SMD = 0.28, (P = 0.000), executive function; SMD = 0.35, (P = 0.000), attention; SMD = −0.19, (P = 0.1), gait speed; SMD = 0.26, (P = 0.007), dual-task cost; SMD 0.56, (P = 0.000), and balance; SMD 0.36, (P = 0.004).
Conclusion: Primary analysis showed a small-to-medium positive effect of dual-task training interventions on cognitive functions and medium-to-large positive effect on gait functions and balance.

Key words: Dual-task training, cognitive functions, gait speed, balance, mild cognitive impairment, dementia, Alzheimer’s disease.


 

 

Introduction

Owing to the upswing in the aging population the number of patients with Alzheimer’s disease and dementia is soaring, which poses a significant global healthcare challenge (1). With no reliable cure for these conditions, healthcare professionals are looking for an affordable and effective treatment (2). At present, there are about 50 million cases of dementia globally, and the number is expected to reach over 75 million by 2030 (3). The informal annual healthcare costs of dementia and Alzheimer’s disease account for 81.3% of the total care costs in China, and they are expected to further raise up to 114.2 billion US$ by 2030 (4). Disappointing results from the available clinical trials and laboratory findings suggest that finding a single treatment for dementia is very unlikely (5). Therefore, the focus is on the development of preventive and early treatment strategies for the cognitive decline during the early stages or preclinical stage of dementia (2, 6). One such particular stage of interest is subjective cognitive decline, which refers to the early stage of cognitive decline, manifesting as worsening of memory and diminished thinking skills, despite preserved cognitive functions based on traditional neuropsychological tests (7). These patients show a pattern of hippocampal and cortical atrophy and is considered a transitional phase between normal aging and dementia (8). In contrast, in MCI patients, other processing abilities such as attention, planning, organizing, perception, learning, reasoning, and judgment are also affected, in addition to memory loss (9). Depending on various conditions the annual conversion rate of MCI to dementia is between 5% and 20% (10). Dementia is a progressive and severe cognitive decline with motor deficits and behavioral problems, which can lead to decline in the ability to perform activities of daily life (1). Alzheimer’s disease, the most common type of dementia (60%–80% of all cases) is a progressive condition that affects memory, thinking, and behavior (11). It is believed that older people with subjective cognitive decline may be an ideal group for starting early preventive intervention programs. These patients are at a high risk of developing pathological cognitive decline in the future, and therefore, early intervention could improve their clinical outcome and reduce future burden on the healthcare system (12).
Cognitive deficit in older adults is strongly association with impaired spatiotemporal gait parameters such as slowing of gait and high stride time variability (13). It is believed that slow gait speed is the early sign of cognitive decline and an indicator of shorter life expectancy (14). In fact, it has been shown in a recent retrospective study that slow gait velocity and high gait variability occur up to 25 years before the accentuated cognitive decline (15). Higher gait variability is strongly associated with a greater degree of cognitive impairment and increased risk of fall in older adults (16).
It is possible to slowdown the progression of MCI, or even reverse the incidence of dementia through various interventions (17). Recent studies have shown that regular physical activity is very effective in reducing cognitive decline and enhancing brain functions and neurogenesis in older adults with MCI (18). Cognitive training and cognitive rehabilitation have also been reported to improve cognitive functions in older adults (19). Results from epidemiological studies have suggested that dual-task training (simultaneous or subsequent combined physical and cognitive training) may have far better results on physical and cognitive performance than either of them alone (20). Recent systematic analyses have shown that combined intervention can significantly improve cognitive functions in older people with or without dementia (21, 22). It has been suggested that dual-task training may induce combined effects of physical exercise and cognitive training (23). Physical exercise is believed to facilitate synaptic plasticity and cell proliferation, while cognitive training guides these newborn neurons into synapses with preexisting neural networks (24-26). Animal studies have shown that physical activities performed in a cognitively challenging environment are more beneficial in inducing neural and cognitive benefits than physical activities alone (27, 28). Several meta-analyses have shown that dual-task training is very effective in enhancing global cognitive function, memory, executive function, mood and activities of daily life in adults with cognitive decline (23, 29). Therefore, the hypothesis that, if dual-task training can improve cognitive and physical functions in cognitively impaired patients, the progression of subjective cognitive decline and mild cognitive impairment into Alzheimer’s and dementia could be halted. Furthermore, improvement in balance and gait will reduce the risk of fall and improve functional independence. These benefits are enormous and their clinical application will be highly appreciated.
Although several reviews and meta-analysis have highlighted the benefits of dual-task training, they have a few shortcomings. Firstly, the quality of their included studies is not very high and the majority had not included randomized control trials. Secondly, their main focus was on cognitive benefits only and had not evaluated changes in motor functions such as gait speed, dual task cost and balance. In fact, to date, there have been no such studies that have focused on the overall effects of dual-task training in individuals with subjective cognitive decline, mild cognitive impairment, dementia, and Alzheimer’s disease. The aim of this systemic review and meta-analyses was to assess the effects of dual-task training on cognitive and motor functions in older adults at various stages of cognitive decline. The secondary aim was to quantify the effects of DTT on global cognition, memory, executive functions, attention, gait speed, dual-task gait cost, and balance in the chosen population.

 

Methods

The review was registered in the International Prospective Register of Systematic Reviews (PROSPERO, https://www.crd.york.ac.uk/) on 5th July 2020 and is available at, https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020179392. The study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines (30).

Search strategy

A systematic search was performed in MEDLINE, PUBMED, EMBASE, EBSCO, Cochran library, and Google scholar databases for papers published in English from inception to 30th September 2020. Search terms were intersections of cognitive intervention terms (subjective cognitive decline “cognitive training” OR “cognitive intervention” OR “memory training”), AND physical intervention terms (“exercise” OR “physical training” OR “aerobic training”), AND aging population terms (“aging” OR “aged” OR “older”), AND combined intervention terms (“combined” OR “combination” OR “multimodal”). Reference lists of the selected papers and related review papers were further screened and additional search of the gray literature and unpublished articles was performed.

Selection criteria

Studies were considered eligible if they met the following inclusion criteria: 1) randomized control trials (RCT); 2) older adults with SCD, MCI, dementia, or Alzheimer’s disease; 3) dual-task training; 4) having a control group for comparison (physically active or cognitive intervention, placebo, and health education). The exclusion criteria were as follows; (1) non-RCT study design; (2) case studies ;(3) review articles; (4) unpublished articles, theses, and dissertations; (5) study protocols; and (6) studies published in languages other than English. In accordance with the Cochrane Handbook of Systematic Review of Interventions, two authors (N Ali and H Tian) independently selected search results based on their titles and abstracts. Eligible articles were further screened for full-text assessment. Disagreements about the eligibility of studies were resolved by discussion with a third author (Y Zhu). The flow chart of study selection and numbers of included and excluded studies is shown in Figure 1.

Figure 1. Prisma flow diagram of the studies selected

Prisma flow chart of the systemic review and meta-analysis.

 

Data extraction, processing, and analysis

The main outcomes of interest were objective measures of cognitive functions and changes in motor function. Based on the popular classification used in a recent meta-analysis, cognitive outcome measures were further grouped into global cognition and cognitive domains (memory, executive function, and attention), while changes in motor functions were grouped into gait speed, dual-task gait cost, and balance. The two authors extracted data independently using spreadsheets for each study, including the information about the methodology, study population, type of intervention, delivery, frequency, duration, outcome measures, and any follow-up if present. In most of these studies, the selected outcome summary statistics were, mean difference (MD), standard deviation (SD), and number of participants before and after the intervention. If MD and SD were not available, standard mean difference from baseline, confidence interval (CI) (95%), P- and F- values, and regression coefficient were used. Open Meta [Analyst] OSX Yosemite (10.10), was used for data processing (31), while RevMan V5.4 was used for data analysis (32). In this meta-analysis we have used continuous outcome data (MD, SD, n) when the same measurements were used, however when different measures for the same outcome were used, we took standardized mean difference (SDM) to obtain their summary effect. The random-effects model was used if significant heterogeneity was found among the included studies so as to pool the effect with 95% CI; otherwise, the fixed-effect model was used.
I2 statistic was used to examine the heterogeneity of the included studies. As a general rule, large I2 of more than 75% suggests high heterogeneity, less than 60% represents moderate heterogeneity and less than 40% indicates low heterogeneity; therefore, we only pooled studies when I2 was below 60%. To determine the causes of the heterogeneity, we conducted sensitivity analysis by eliminating the included studies one by one to identify the study that is heterogeneous, and to see if the I2 statistics changed substantially. We also conducted subgroup analysis to modify the effects of the outcomes and to obtain the two-sided p-value (< 0.05 represents significant effect) (33). Furthermore, funnel plots were used to assess the publication bias and to identify outliers, studies that fall out of the normal funnel plot. Effect size was considered small (d=0.2), moderate (d=0.5), and large (d=0.8).

Risk of bias assessment

The Cochrane risk of bias assessment tool was used to measure the quality of the included studies (34). Here the risk of bias is reported in six domains, these are, selection bias, performance bias, detection bias, attrition bias, reporting bias, and other bias. These domains were rated as low, high, or unclear. Both authors (N Ali and H Tian) independently performed the risk of bias assessment and any difference in the outcome was resolved through discussion with a third author (Y Zhu). The total risk of bias judgment was obtained based on the accumulated assessment of all the above domains and is presented in Figure 2.

Figure 2. Risk of Bias assessment

Risk of bias assessment using Cochran collaboration’s risk of bias assessment tool (RoB).

 

Results

A summary of the selection process is shown in Figure 1. The initial database search provided 443 relevant articles, out of which 408 were identified through the actual databases and 35 from additional sources. After the removal of the duplicates 409 remained, out of which 91 articles were selected for full-text inclusion. The reasons for exclusion the remaining studies were, irrelevant population (n=159); in-eligible design (n=85); thesis, dissertation, protocols (n=32); irrelevant interventions (n=24); review papers (n=11); and non-RCTs (n=7). Full-text scanning of the 91 articles resulted in excluding certain studies due to irrelevant outcome (n=32); no cognitive or motor outcomes (n=10); single-tasking (n=12); healthy controls (n=10); lack of control group (n=5); and published in languages other than English (n=1). Finally, two more studies (n=2) were added after cross-referencing and of the total articles, a total of 21 articles were included in the qualitative analysis and 20 papers were used for quantitative analysis.

Characteristics of the included Studies

Table 1 provides a summary of the included studies. There were 11 (n=11) studies with Mild cognitive impairment patients and the total number of the included individuals was 1176 (Intervention group 1176 and 1168 in the control group). There were four studies with dementia patients (n=4) and the total number of people in these studies was 345 (1153 in the intervention group and 142 in the control group). There were four studies of patients with subjective cognitive decline (n=4), where the total number of participants was 410 (Intervention group 207 and 203 in the control group). The remaining two studies (n=2) were of patients with Alzheimer’s disease and there were 290 participants in these studies (200 people in the intervention group and 90 in the control group). The majority of the included studies were from Japan (n=5), followed by Canada (n=4), Germany (n=3), and Italy (n=2). The remaining studies were carried out in Belgium, France, Finland, Hong Kong, Korea, Slovakia, and Taiwan.

Table 1. Characteristics of the included studies

AD, Alzheimer’s disease. MCI, mild cognitive impairment. SCD, subjective cognitive decline, MMSE, mini mental state examination. MoCa, Montreal cognitive assessment. CDT, clock drawing test. STD, Stroop word color test. RCT, randomized control trail. GCF, global cognitive functions.

 

Primary and secondary analysis

Effect of dual-task training on global cognitive function

Primary analysis showed that dual-task training had low-to-moderate effect on global cognitive function in older adults with SCD, MCI, and dementia or Alzheimer’s disease (SMD = 0.24 [0.11; 0.36], 95% CI, Z = 3.37, and P= 0.002). Furthermore, secondary analysis significantly reduced heterogeneity across the studies (Ch2 = 5.74, I2 = 0%, Figure 2). The overall effect for subgroup MCI, SCD, and dementia patients was low-to-moderate (SMD = 0.29 [0.16; 0.43], Z= 4.18, P= 0.000), and was negative for Alzheimer’s disease patients (SMD = −0.02 [−0.31; 0.28], Chi2 = 5.92, P=0.82), without significant heterogeneity (I2 =0%). Furthermore, funnel plot did not reveal risk of publication bias (Figure 3b).

Figure 3a. Pooled effect of dual-task training on global cognition

Forest plot efficacy of combined cognitive physical intervention compared to control group on global cognitive function. Study ID, mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), random effects model.

 

Figure 3b. Funnel plot of dual-task training on global cognition

Funnel plot showing symmetrical distribution of studies indicating absence of publication bias.

 

Effects of dual-task training on domain-specific cognitive function

Effects of Dual-task training on memory

Figure 3c shows the combined effect of dual-task training on memory calculated with random effects model. Earlier there was high heterogeneity among the studies therefore, secondary analysis between various groups was performed that reduced heterogeneity significantly. SD mean with CI 95% for MCI, dementia and Alzheimer’s was 0.33 (0.2, 0.47), effect size Z = 4.81, and P = 0.000, while for subjective cognitive decline was SDM = 0.09 (-0.18, 0.37), Z = 0.68, and P =0.5. In addition there was no heterogeneity among these studies (I2 = 0%.). Furthermore the overall effect of dual task training on memory was SMD = 0.28 (0.16, 0.41), with Z = 3.75, and P = 0.000.

Figure 3c. Forest plot of the effects of dual-task training on memory

Forest plot efficacy of combined cognitive physical intervention compared to control group. Study ID, Mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), weight indicates influence of individual study on the pooled results, random effects model. MCI mild cognitive impairment, AD Alzheimer’s disease, SCD subjective cognitive disorder.

 

Post-intervention effects of the dual-task training intervention on executive function

Figure 3d shows that dual task training had moderate effect on executive function calculated through the random-effects model. Mean SD with 95% CI was 0.35 (0.23, 0.48), with Z = 5.43 and P = 0.000. In addition, heterogeneity was low among the studies included (I2 = 8%).

Figure 3d. Forest plot of the effects of dual-task training on executive function

Forest plot efficacy of combined cognitive physical intervention compared to control group. Study ID, Mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), random effects model.

 

Post-intervention effects of dual-task training on attention

The results of the random effects model analysis showed that dual task training has a low impact on attention; {SMD −0.19 (0.42, 0.4), Z= 1.63, and P = 0.1}. There was no heterogeneity among the included studies; (Chi2 = 1.94, P = 0.86, and I2 = 0%). One study (Maffeil et al. 2017) was excluded based on visual inspection of the funnel plot and was considered an outlier. Furthermore, attention was measured with Trail Making Test part-A by majority of the included studies (n=3), while two had (n=2), used the Strop test and one study (n=1) had used Digit Symbol Test as their measuring tool. The negative sign of the results indicate a reduction in time to complete the test representing improved attention. The results are shown in Figure 3e.

Figure 3e. Forest plot of the effects of dual-task training on attention

Forest plot efficacy of combined cognitive physical intervention compared to control group on attention. Study ID, Mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), random effects model.

 

Post-intervention effects of dual-task training on physical functions (gait parameters)

Effects of dual-task training on gait speed

Figure 4a shows the overall effect of dual-task training on gait speed calculated through the random effects model. Mean SD with 95%CI was 0.35 (0.17, 0.54), Z = 3.72, Chi2 =6.5, and P = 0.000 for subgroups SCD, MCI and dementia. The pooled effect of gait speed for Alzheimer’s disease patients was −0.17 (−0.5, 0.16), Z=1.02, P = 0.31. Subgroup analysis highly reduced heterogeneity among the included studies, while the overall effect size was 0.26 (0.04, 0.49), Z=2.26, and P= 0.02. The two groups were significantly different from each other Z=7.3, P= 004 and I2 = 86%.

Figure 4a. Forest plot of the effects of dual-task training on gait speed

Forest plot efficacy of combined cognitive physical intervention compared to control group on gait speed. Study ID, mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), random effects model.

 

The impact of dual-task training on dual-task gait cost (DTC)

The result showed that dual-task training had huge impact in reducing dual-task gait cost {SMD 0.65 (0.24, 0.88), Z= 3.4, and P = 0.000}. In addition there was low heterogeneity among the studies included (Chi2 = 2.88, P = 0.41, and I2 = 27%). Dual-task gait cost was measured as the percentage of the rate of dual tasking subtracted the rate of single tasking divided by rate of single tasking (35). The results are shown in Figure 4b.

Figure 4b. Pool effect size of the effects of dual-task training on Dual task gait cost

Forest plot efficacy of combined cognitive physical intervention compared to control group on dual task gait cost [(dual-task RT – simple RT) / simple RT Å~ 100]. Study ID, mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), random effects model.

 

Effects of dual-task training on balance

Results of the random effects model analysis showed that dual task training had low-to-moderate impact on balance {SMD 0.36 (0.12, 0.61), overall effect Z= 2.87, and P = 0.004}. In addition there was no heterogeneity among the studies included (Chi2 = 4.64, and I2 = 0%). Furthermore, balance was measured with different measures by these studies, which were, Tinetti-POMA scale (Performance-oriented Mobility Assessment), Disjunctive Reaction Time (DRT-II), Falls Efficacy Scale International (FES-I), and Timed Up and Go test. The results are shown in Figure 4c.

Figure 4c. Forest plot of the impact of dual-task training on balance

Forest plot efficacy of combined cognitive physical intervention compared to control group on balance. Study ID, mean difference between pre and post intervention, N= number of patients, SD standard deviation, StD standardized mean difference (95% confidence interval), random effects model.

 

Discussion

This review and meta analysis extend our knowledge of the beneficial effects of dual-task training on cognitive and physical functions in older individuals at various stages of cognitive impairment. In addition, here we have quantified the effects on global cognitive function, memory, executive function, attention, gait speed, dual task cost and balance. Twenty-one RCTs published between 2010 and 2020 were included in this study, representing relatively new and emerging field of research.
To our knowledge, this is the first meta-analyses about the effects of dual-task training on cognitive and motor functions in cognitively impaired older adults. By summarizing the findings of 21 RCTs of older individuals at various stages of cognitive impairment, we have analyzed the effects of dual-task training on cognitive and physical functions. A small effect size of dual-task training was found on global cognitive function and attention domain, while low-to-moderate impact on memory and executive function. We have also found low-to-moderate impact on gait speed and balance, and moderate-to-high impact on dual task cost. Surprisingly, a minimal-to-low negative impact of dual-task training was found on global cognitive function and gait speed in Alzheimer’s disease patients and minimal-to-low positive impact on memory in subjective cognitive decline patients. This might be due to the limited number of available studies in this population, stage of the cognitive impairment, and/or other age-related dysfunction (36).
Our results are in line with the findings of other reviews and meta-analysis carried out on the same population and same intervention (22, 29). These reviews have found low-to-medium effect on global cognitive function, although they had included older adults with and without cognitive problems and have also included non-RCTs in their review. Karssemeijer et al. (2017) have also reported a mild-to-moderate on executive function, attention and memory, although, attention and executive function was considered as a single domain in their study. In addition, Bruderer-Hofstetter et al. (2017), and Yang et al. (2019), have also reported similar findings in cognitive and physical performance (37, 38). Furthermore, only a few studies have focused on changes in motor functions such as gait speed and balance in individuals with cognitive impairment; thus, no reviews are available about the impact of dual-task training on dual-task cost. This might be due to the limited number of studies with gait function outcome.

Strengths, limitations and future recommendations

The main strength of our review and meta-analyses is that the evidence is much stronger than the previous reviews because we have included RCTs only. The data used to synthesize the estimated pool effect size were obtained from articles searched through a wide range of databases that reduced the incidence of bias. The aim of this meta-analysis was not only to evaluate the impact of dual-task training on older adults with cognitive problems, but also to replicate previous findings while addressing methodological and heterogeneity problems. In addition, we have analyzed the outcomes of cognitive function as well as physical outcomes, which have not been addressed before. Our findings support the clinical application of dual-task training for patients at various stages of cognitive decline. Although the intensity, duration, frequency and contents of our intervention (dual-task training) are different its cognitive and motor benefits are immense and can lead to improved mental capabilities, better coordination, fall prevention and independent life. Therefore devising a combined mind-body training program for older adults with dementia and Alzheimer’s disease could be a very good strategy for the prevention and rehabilitation of cognitive decline and fall prevention.
The findings from this study should to be considered in the context of several methodological limitations. In particular, variations of the intervention, duration, frequency, settings and the classification of cognitive impairment was not consistent among the included studies. Complexity of the dual-task and systematic differences between population groups base statistics makes the findings of this meta analysis prone to bias and differential outcome. In addition we have only included RCTs published in English and might have missed studies published in other languages. Furthermore, all the interpretations in the current meta-analyses are based on the estimated effect size and not the actual outcome; therefore, these results should be considered with caution.
Future research should focus on domain specific intervention for cognitive problems in older individuals and should aim at slowing down or preventing progression of cognitive impairment in MCI, dementia or Alzheimer’s disease. In addition, further research is needed to establish the optimum intervention intensity, duration, and frequency of dual-task training for long lasting impact. Furthermore researchers should ideally use a standardized protocol for the studies to be more conclusive and facilitate interstudy comparisons.

 

Conclusion

To conclude, this review and meta-analysis support the notion that dual-task training is an effective non-pharmacological intervention, which can improve cognitive and physical functions in older people with cognitive impairment, when compared to other therapies. We have found that 2–5 sessions (30-–120 minutes) of dual-task training per week has the potential to improve global cognition, executive function, attention and memory in cognitively impaired older adults. There is also evidence that such training programs can enhance physical functions such as gait speed, reduce dual task cost, and improve balance. These findings support that dual-task training impart diverse cognitive and physical improvements for older individuals with cognitive diseases. However, long-term studies are needed to determine the effectiveness of dual-task training in the wider community and whether or not such effects can be sustained in the long term.

 

Ethical approval and consent to participate: not applicable.

Consent for publication: All the authors agreed the manuscript for publication.

Availability of data and material: All the data could be made available on request.

Conflict of interest: The authors declare that this research was conducted in the absence of any commercial or financial relationships that could be considered as potential conflict of interest.

Author Contributions: Yi Zhu: Completed the funding application managed and coordinated the study and drafted the initial protocol and registration. Tong Wang: Provided the research ideas and revised the manuscript. Nawab Ali, Huifang Tian: Database search, study selection, data collection, analysis, interpretation and manuscript draft. Qian Zhong, Yaxin Gao, Han Wu, Cuiyun Sun: Revised the study design, data process and interpretation. Lehana Thabane, Jinhui Ma: Study design, guided statistical analysis and manuscript.

Funding: This work was funded by National Natural Science Foundation of China (NSFC) (Grant No. 81802244), and National Key R&D Program of China (Grant No.:2018YFC 2001600, 2018YFC 2001603) and Nanjing Municipal Science and Technology Bureau (Grant number of 2019060002).

Acknowledgments: The authors would like to thank all the authors of the included trails and their participants. We also like to thank Majid Yousafzai from Nanjing medical university for his contribution and guidance.

Trail registration: CRD42020179392.

 

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