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The Motor-cognitive Training on Cognition and Physical Performance in the Older Adults with Mild Cognition Impairment : A Literature Review

Objective: Older adults with mild cognitive impairment (MCI) are more likely to progress to dementia. Motor-cognitive training is applied as a dual-task to improve the cognitive and physical functions of older adults with MCI. The purpose of the study was to know the recent trends in motor training types and outcome measures used for motor-cognitive training in older adults with MCI. Methods: This literature review was conducted in Pubmed, MEDLINE® and Google Scholar with the following key words: older adults, mild cognitive impairment, motor-cognitive training, cognition, and dual-task. The 7 studies were found with the search tool and all studies were randomized controlled trials. Results: In motor-cognitive training in older adults with MCI, 6 studies applied aerobic exercise. And 3 out of 6 studies also applied strengthening exercises. One study applied dual tasks without aerobic exercise. In the 6 studies, overall cognitive and executive function were used as outcome measures, and physical function was evaluated as gait performance. Memory and physical frailty were also used as measurement tools. As a result of all studies, when motor-cognitive training was applied, cognition and physical performance showed significant results. Conclusions: A recent five-year study applied mainly aerobic exercise and strength training to older adults with MCI and found it to improve cognitive and physical performance.

There are previous studies that showed the effect of cognitive ability and physical function by applying exercise training with cognitive training for cognitive improvement of the older adults [9,14,15]. Motor-cognitive training is beneficial to enhance cognitive and physical function even for older adults with MCI [3,16]. In the method of applying motor-cognitive training, applying tasks at the simultaneous has an advantage in cognitive improvement than applying them sequentially [17].
Recently, dual-task training using virtual reality (VR) [18,19] and aerobic exercise [20] have been mainly implemented for motor-cognitive training. Aerobic exercise significantly increases functional activation of MCI brain regions and helps to effectively improve cognitive function [21]. The improvement of physical function and cognitive ability through exercise training has raised the possibility that biological pathways and neural substrates may be shared between them, but the exact mechanism has not yet been elucidated [9,22]. Nevertheless, studies that improve cognition through exercise training continue to be published.
Therefore, this study intends to identify the latest trends by reviewing recent studies related to motor-cognitive training, which is mainly conducted in an environment similar to real life. And to suggest what the ideal motor-cognitive training is for in the older adults with MCI.

Data sources and study criteria
The collection of theses was conducted by 3 physical therapists using selected keywords, and the collected documents were organized, compared, and analyzed through a bibliographic information program (EndNote 20, Thomson Reuters, USA). In the case of inconsistency between the abstract and the main text of the thesis during the selection process, it was excluded from the collection process( Figure 1).
The study criteria used in the analysis of this study Figure 1. flow diagram were as follows: (1) studies in which subjects were diagnosed with MCI, (2) a study applying dual-task for motorcognitive training, (3) a study that included cognitive and physical function as an outcome according to each intervention method, (4) a study conducted as a randomized control trails study. In addition, studies on cognitive enhancement of neurological diseases other than MCI, a study written in languages other than English and Korean, and studies that could not accurately explain the effect of motor-cognitive training due to the study design were excluded. In this literature review study, studies from 2016 were searched using the databases of PubMed, MEDLINE® and Google Scholar.

Search terms
The keywords used in the search were as follows and were used either in combination or independently: 'older adults', 'elderly', 'elderly cognition', 'cognitive decline','mild cognitive impairment', 'motor-cognitive training', 'exercise', 'aerobic exercise', 'physical training', 'dual-task', 'cognition', 'cognitive task', and 'physical function'. As a result, the 7 studies were found with the search tool and all studies were randomized controlled trials.

Study selection process
For studies collected through the database, duplicate studies were removed using a reference management program (EndNote 20, Thomson Reuters, USA). After screening through the abstract and title, the original text of the thesis was reviewed according to the selection criteria. In the process of data extraction, general characteristics, specific interventions, and research results were extracted. If the data do not match, the original text was reviewed and finally selected and summarized.

Results
According to our selection criteria, 7 studies were classifiedusing the PICO search strategy (Table 1) (Figure 1). As a result of all studies, when motor -cognitive training was applied, cognition and physical performance showed significant results.
In motor-cognitive training in older adults with MCI, 6 studies applied aerobic exercise. And 3 out of 6 studies also applied strengthening exercises. One study applied dual tasks without aerobic exercise.
In study of Park JH [23], motor training in motor -cognitive training was applied simultaneously with cognitive training such as range of motion (ROM), TheraBand strengthening (low intensity), passing/throwing a ball. And for aerobic exercise, wrist, elbow, shoulder, ankle, knee range of motion exercise and walking motion were sequentially applied for during intervention program.
Kwan et al. [19] was the under-desk ergometer with adjustable cycling resistance was applied alone without combining with other exercises as a motor training during cognitive training using virtual reality program.
Park HT et al. [3] was motor training, aerobic exercise combined activity program was applied. The combined activity program includes a warm-up, stretching training, aerobic exercise, balance exercise, aerobic and cognitive training, resting time with feedback and encouraging active daily living physical education, and cool-down exercise. And the aerobic exercise applied was stair stepping, endurance walking and stair climbing, and walking on an agility ladder. During aerobic exercise, the target heart rate zone was at 55% to 80% of the maximum heart rate in the intervention [24].
Lia et al. [18] were also applied motor training combined with aerobic exercise. And the program was composed of a simplified 24-form Yang-style Tai Chi, resistance exercise, aerobic exercise, ADL relating functional tasks, and included for that to improve upper and lower extremity balance, stability, strength, and endurance.
The motor training applied in the study of Law et al. [25] is warm-up of light stretching, moderate-intensity aerobic exercise, whole-body movement exercise, bicycle, arm ergometry, cool-down exercise. The functional task exercise group was appliedwarm-up, core functional tasks exercise, and cool-down exercise.
Shimada et al. [8] was applied an activity program that combines aerobic exercise, and also included muscle strengthening, and postural balance training. Aerobic exercise includes climbing stairs, endurance walking, and walking on a balance board. Average aerobic exercise intensity was 60% to 80% of maximum heart rate (HR) identically with previous studies [24].
In the 6 studies, overall cognitive and executive function were used as outcome measures, and physical function was evaluated as gait performance. Memory and physical frailty were also used as measurement tools. Of the 7 studies, 3 studies [18,19,23] were using a montreal cognitive assessment (MoCA) as eligibility criteria were, and 1 study [1] was using a Korean version of mini-mental state examination (MMSE-K). For cognitive evaluation of motor-cognitive training, a trail making test A and B (TMT-A/B), the stroop color-word test (SCWT) to evaluate executive function were mainly used, and MoCA, modified alzheimer's disease assessment scale-cognitive subscale (ADAS-Cog), and MMSE were used for overall popular intelligence. Memory function was evaluated by a digit span test forward and backward (DST) and Chinese version verbal learning test (CVVLT).

Discussion
As a result of analyzing a recent study applied for motor-cognitive training to older adults with MCI, it was confirmed that the dual-task was applied simultaneously, and that motor training was applied either alone or in combination with aerobic exercise as an activity program. Therefore, simultaneous application of aerobic exercise and cognitive tasks will be an intervention method that can lead to improvement in cognitive ability and physical function.
In the study of Park HT et al. [3], the physical and cognitive combined intervention program applied increased the prefrontal cognitive function of MCI, and Shimada et al. [8] was find out the volume loss in the left brain hemisphere was smaller than the right during of the motor-cognitive exercise. Park JH [23] described a significant decrease in HbO 2 in the prefrontal lobe during executive function tests as an increase in the neural efficiency. According to the results of these previous studies, the brain volume over 65 years of age decreases by 0.5% to 1% annually due to normal aging, and the hippocampal volume decreases by 1% to 2% even in the absence of dementia [26], resulting in a higher risk of cognitive impairment. Therefore motor-cognitive training could expect applied as a good arbitration method.In particular, executive function can improve through aerobic exercise, and neural activation improves neural efficiency in areas where aerobic training supports executive processes of selective attention and response inhibition [27].
The MoCA, which was used the most in previous studies analyzed in this study, was developed to distinguish mild cognitive impairment [28] and is said to show higher diagnostic accuracy than MMSE [29,30]. And a TMT-A/B used to evaluate executive function is the most famous neuropsychological test and can be applied in various ways considering age and educational level [31]. It was confirmed that most studies evaluated cognitive function using similar outcome measures.
A recent motor-cognitive training study for MCI was conducted in virtual reality, but it was also conducted with content related to daily life tasks. In any environment, positive effects of cognitive ability and physical ability can be derived by applying the combination of body movements including aerobic exercise and tasks related to real life. It is believed that good results can be drawn if future experimental studies are conducted with these results as a reference.