Dual-Task Training with Cisual Stimulation Affect Cognitive and Physical Performances and Brain Wave Ratio of Patients with Alzheimer's Disease: A Randomized Controlled Trial

Background: This study aimed to investigate the effect of a 12-week period dual-task training on cognitive status, physical performance and brain waves of patients with Alzheimer's disease (AD). Methods: Twenty-six AD patients were randomly assigned to two groups, training group (TG) and control group (CG). TG executed progressive combined exercises with visual stimulation twice a week for 12 weeks. Training included muscle endurance, balance, exibility and aerobic exercises with eyes closed and opened. Brain waves on EEG and a series of physical, cognitive and mental tests were taken prior and post intervention. Results: There was a signicant improvement after training protocol in cognitive function, particularly in short-term memory, attention, working memory and executive function (p<0.01). In addition, there were substantial improvements in depression status (GDS scale), aerobic tness (6 min walking), exibility (chair sit and reach) functional ability (chair stand, timed up and go test), strength (knee extensions, preacher biceps curl, handgrip) in TG compare to CG. These progresses was associated with signicantly increase (p<0.05) in the frequency of brain waves and decreased in the theta/alpha ratio. Conclusions: In addition to physical performance, the regular combined training with visual stimulation improve brain health as indicated by improving cognitive function and reducing the theta/alpha ratio. Trial registration: Iranian Registry of Clinical Trials,

Epidemiological evidence suggests exercise training as a non-pharmacological approach to protect against AD (10,11), increase the hippocampus size (12), and increase brain neurogenesis (13). These structural changes are associated with functional improvements, such as improved independence and cognition of AD patients (11). Moreover, these exercise-induced brain changes are associated with alterations in the power of brain waves. However, to the best of our knowledge, there are no studies investigating the effects of physical training on the frequency of brain waves in AD. In this regard, Gutmann et al. (2015) reported that the individual alpha peak frequency remained unchanged after four weeks of moderate exercise training in healthy individuals (14). Also, researchers have reported that acute bouts of exercise increase the power of beta waves in the frontal and central areas of the brain, which may indicate an increase in cortical activation (15,16); however, the long-term effects of physical training are unclear.
Researchers have shown that brain activation during exercise (a dual-task exercise) is bene cial for cognitive function (17,18). Generally, training with eyes closed and remembering to do speci c exercises with several stations are simple mental activities. In this regard, Hutt and Redding (2014) showed that an eyes-closed dance training increased the dynamic balance of ballet dancers (19), as closing the eyes led to a shift from visual to proprioceptive dependence for balance control. Moreover, researchers have found that closing the eyes activates different areas of the brain, especially the amygdala, which is involved in memory and learning (20,21).
According to some researchers, unlike other waves, the power of alpha waves increases in a resting state with the eyes closed (22), whereas it differs when the person focuses on performing activities with the eyes closed. Dual task exercises can be used to maintain the brain structure and function and improve physical independence in AD patients. Accordingly, eyes-closed exercises can activate the brain areas involved in memory to focus on activities; they may also increase alpha and beta rhythms.
Overall, AD causes disorders in different physical and mental functions. To the best of our knowledge, this is the rst study to assess the effects of combined physical training with visual stimulation on the physical and cognitive functions of patients with AD. It is known that the power of brain waves re ects brain changes and that AD increases the theta/alpha ratio. Accordingly, we hypothesized that physical training combined with mental challenge could modify the power of brain waves. In this study, we aimed to investigate the effects of combined training with visual stimulation on the theta/alpha ratio, as well as cognitive and physical health of patients with AD.

Study design
This randomized clinical trial, with control and parallel groups, phase two, and single-blind design was conducted on patients with AD. We aimed to investigate the effects of a 12-week, low-intensity training, combined with visual stimulation, on the brain waves (alpha, beta, and theta), cognitive and physical Before and after training, the participants underwent a series of tests. All training sessions and tests were performed at Roozbeh Hospital Medical Center under the supervision of a sports medicine physician.

Cognitive status
The Montreal Cognitive Assessment (MoCA) test, developed by Nasr al-Din et al. for MCI and dementia, evaluates different domains of cognitive functioning. The reliability of this test was 92%, based on Cronbach's alpha, and its internal consistency (IC) was 83% (24). The maximum score of the test is 30, with a score of 26 or higher considered to be normal. This test, which is executed within 10 minutes, includes different domains: short term memory (5 points); executive function, including Trail Making Test B (TMB), Clock Drawing Test (CDT), and visuospatial function test (cube copying) (5 points); attention and working memory (6 points); language, including naming, repetition, and uency (6 points); abstraction (similarity) (2 points); and orientation to time and place (6 points). Patients with scores of 26 or higher did not have any cognitive impairments (normal MoCA), whereas patients with scores lower than 26 probably had cognitive impairments.

Depression questionnaire
The Geriatric Depression Scale (GDS) was used to assess depression in the participants. In this questionnaire, all questions are of similar weight and have a yes/no response format. The maximum score of GDS is 15, and the minimum score is zero, with higher scores indicating more severe depression. This scale is one of the best tools for measuring depression in the elderly and patients with dementia.
Sensitivity of 92% and speci city of 89% have been reported for this questionnaire (25). The validity and reliability of 15-item GDS were measured by Malekouti et al. in Iran, and the best cut-off point was eight, with 90% sensitivity and 84% speci city (24).
The 15-item GDS captures depressive symptoms over the past week, using a yes/no response format. For ten items, a positive response ('yes') is given a score of one, and for ve items, a negative response ('no') is given a score of zero. Also, ve items are reverse-scored (one for 'no' and zero for 'yes'). The total score of the items ranges from 0 to 15, with higher scores indicating more depressive symptoms. The GDS-15 score has been used as both continuous and categorical variables elsewhere. We used a cut-off score of ≥ 5 to indicate the presence of clinical depression symptoms (0, GDS-15 score < 5 and 1, GDS-15 score ≥ 5). We also considered the continuous score of GDS-15 as the outcome (26-28).

Maximum strength
The maximum strengths of knee extensions, preacher curls, and handgrips were measured for all participants. One-repetition maximum (1-RM) for leg extensions and preacher curls was also determined, based on the procedures described by Sheppard and Triplett (29). The participants performed a general warm-up, consisting of ve-minute pedaling on a stationary bicycle (50-70 rotations per minute at a resistance level of 1-5), followed by a speci c warm-up of two sets (5-20 repetitions at 40-50% of perceived maximal effort). Next, they made 3-5 attempts to reach 1RM, with 3-5 minutes of rest between attempts.
For knee extensions, the participants were asked to sit on a machine (Impulse IT95 Leg Extension, Impulse Health Tech Co. Ltd., Shandong, China). The researcher adjusted the chair in a way that the subject's legs were placed under the pad, and his/her feet pointed to the pad, while extending the knees.
In preacher biceps curls, the participant adjusted the preacher bench, held a dumbbell with fully extended arms, and curled it up to shoulder level. Also, a grip strength dynamometer was used to measure the maximum isometric strength of the hand and forearm muscles. After adjusting the handle of the dynamometer for the subjects, they were asked to hold it in their hands, while keeping the arms at the right angles and the elbows on two sides of the body. Participants pressed the dynamometer with maximum isometric effort, which was maintained for about ve seconds (30). The best result of the three trials was recorded for each participant.

Functional tests
The timed up and go (TUG) and chair stand tests were used to measure functional abilities. The TUG test requires the participant to stand up from a chair without the use of arms, walk 2.4 meters, turn, return to the chair, and sit (31). Also, the chair stand test requires the participant seated on a chair to stand up as many times as possible within 30 seconds. The participants were instructed to keep their arms crossed at the wrists and hold them in front of the chest. The examiner counted the number of stands performed correctly within 30 seconds (32). Chair sit and reach (CSR) test requires the participant to sit on the edge of a chair, with one foot at on the oor and the other leg extended forward with the knee straight and heel on the oor. By placing one hand on top of the other, the subject stretched his/her hands toward the toes by bending at the hip. Next, the distance between the tip of the ngertips and the toes was recorded as a score. If the ngertips reached the toes, the score would be zero; if the ngertips did not touch the toes, the score would be negative; and if the ngertips overlapped, the score would be positive. Overall, two trials were conducted for each participant, and the best distance was recorded (31). The Six-minute walk test (6MWT) was designed to assess aerobic tness. In this test, the participants walked at a selfselected pace and were allowed to stop or change their pace (32). In the indoor setting, two cones were placed 30 meters apart, and the participants were asked to walk back and forth. The walking path was marked every one meter to determine the distance accurately. For safety, a supervisor accompanied the participants.
Brain waves Electroencephalography (EEG) (SOMNO medics, SSP full EEG, Germany) was used to evaluate the brain waves with high sensitivity. The information related to beta, theta, and alpha changes on EEG test, investigated by a neurologist, was used to determine the patient's status. EEG was obtained over ten minutes, and then, the percentage of each brain wave and the brain wave index were extracted, based on the visual scale. We also divided theta power by alpha power to calculate the theta/alpha ratio.

Training protocol
The participants in the experimental group performed 24 workouts twice a week for 12 weeks. Each session lasted about 40-60 minutes, including ten minutes of warm-up, 20-40 minutes of main exercises, and ten minutes of cool down. The participants adhered to a combined protocol, including simple brain activities (eyes-closed training and cognitive activities) and physical activities (muscle endurance, balance, and aerobic capacity). The main training protocol consisted of ve parts.
The rst part of the training protocol included sitting and standing on an armchair, accompanied by shoulder girdle strengthening (three sets with 5-15 reps, followed by a gradual increase in resistance and repetition, using dumbbells and TheraBand). The second part included crossing over ve sponge obstacles (height: 15-20 cm) with eyes closed (two repetitions in the rst three sessions, gradually increasing to two reps every three sessions); the distance between the obstacles was variable. In the third part, the participants crossed over a safe balance beam board (2 m) with eyes closed (two repetitions in the rst three sessions, gradually increasing to two reps every three sessions).
In the fourth part, six-vowel stations were placed in a semicircular arrangement at a four-meter distance in front of the subject with eyes closed. The subjects were asked to identify the sound of each station, move toward it, perform the predetermined exercises for 15 seconds (e.g., butter y curls, Hercules curls, knee raises, hand raises, and biceps curls), and return. There were only two stations in the rst session, which increased by one station every three sessions to reach a total of six stations. In the last part, there were four colored lights in front of the participants, each indicating a predetermined exercise. As long as the light was on (10-15 seconds), the subject was required to perform the relevant exercise (e.g., red light: side-right lunge; blue light: side-left lunge; green light: backward right lunge; and yellow light: backward left lunge). This part lasted for two minutes in the rst session, which increased by one minute every three sessions to reach ve minutes by the end.
The exercises changed every three sessions and became more intense. The workouts were performed individually, and each individual attended the center at a certain time. The researcher accompanied the participants throughout training. The intensity of training was di cult due to the variety of exercises. To monitor the workout intensity, heart rate (HR) was monitored by a smart watch.

Statistical Methods
Data presented in mean ± standard deviation (SD). The Statistical Package of Social Sciences (SPSS, IBM, v19) was used to analysis data. A repeated measure analysis of variance ANOVA with the time (T1 vs T2) and protocol (TG vs CG) was performed to analysis data. To assess the magnitude and direction of the linear correlations between percentage change of the performance parameters and perceptual indices (MoCA & GDS), bivariate Pearson's correlation coe cient (r) was calculated. Effect size (ES) was also computed as the change score divided by the SD of the change score to examine the magnitude of differences while controlling for the in uence of the sample size (33) with 0.2 considered as a small ES, 0.5 as a moderate ES and > 0.8 as a large ES (34). The signi cance level was set at p ≤ 0.05 for all statistical analyses. To determine the test-retest absolute and relative reliability, the coe cient of variation (CV) and intra-class correlation coe cient (ICC) was calculated. The ICC was calculated by a two-way single measure absolute agreement model and the CV was calculated by formula (CV= [SD/mean] × 100). The CV for tests was < 4.0% and ICC was > 0.98.

Results
The   (Fig. 3). Table. 2 presents the bivariate Pearson's correlation coe cient (r) between the percentage change of performance parameters and MoCA and GDS. In general, there were moderate to large, positive correlations between MoCA changes and performance induces. Moderate, negative correlations was found between changes in GDS, and performance induces. In addition, MoCA correlated negatively with theta/alpha ratio, while GDS correlated positively. *** Table 2 near here*** The mean (SD) of HR during the intervention period was presented in the Fig. 4. The training begun at 50% of maximal HR and reached to 70% of maximal HR toward the end of intervention. The range of HR were 80 to 125 beat per minute.

Discussion
This study aimed to evaluate the e cacy of a 12-week combined training intervention with visual stimulation on the frequency of brain waves, cognitive status, and physical performance of patients with AD. The results revealed that following the intervention, patients in the TG group experienced signi cant improvements in cognitive function, particularly short-term memory, attention, working memory, and executive function. We also found signi cant improvements in the depression status of the TG group, compared to CG.
Moreover, signi cant improvements were observed in the overall physical performance of the participants. These improvements were associated with the reduction of the theta/alpha ratio, suggesting that the intervention was effective in involving and activating neurons. Also, moderate to relatively strong correlations were observed between cognitive and performance indices. The ndings of our study revealed that the combination of exercise training with mental challenges (such as closing the eyes, attending to auditory stimuli, and trying to control balance by relying on proprioceptive receptors) can be used to improve the independence of patients with AD.
Cognitive disorders, including memory, speech, attention, and executive function impairments, are among the characteristics of AD, which can be measured with MoCA test in this population. In our study, after the intervention, cognitive performance (MoCA test) improved with a large effect size (28.4%; ηp 2 = 1.7).
Improvements were observed in short-term memory, executive function, attention, and working memory. Also, closing the eyes, as part of our training protocol, activated different brain areas, especially the hippocampus, which are involved in attention, memory, and executive function. Our results are in agreement with previous research, supporting the protective effects of physical training on cognitive function (35,36).
Although the exact mechanisms of the protective effect of exercise training on the mental health of AD patients are less clear, several mechanisms have been proposed, including the increase of blood supply to the brain, improvement of metabolic health, production of neurotrophic factors (37), increased size of the hippocampus (12), and increasing gray and white matter volumes in the inferior parietal cortex and the hippocampus over a long period (35,38). These alterations are associated with memory and cognitive performance, as well as changes in the power of brain waves. In this regard, a previous study showed that even a 12-week period of aerobic training could expedite neuroplasticity and promote brain health in sedentary adults (39); the observed improvements in brain function were attributed to the increased physical activity of the participants.
Depression is one of the most common symptoms and consequences of AD, which exacerbates the negative consequences of this disease. Research has shown that regular exercise training in the shortterm had obvious effects on depression management (40). The results of the present study also demonstrated the effectiveness of combined training in reducing depression. Based on the results, depression was inversely correlated with physical tness indices and positively correlated with the theta/alpha ratio. Several mechanisms can justify the positive effects of exercise on depression. Improvement of independence, daily life activities, and mood is among the advantages of exercise training for reducing depression.
Moreover, exercise-mediated production of neurotransmitters, such as dopamine, serotonin (41), and brain-derived neurotrophic factor (42), contributes to the treatment of depression. Also, AD-induced high cortisol levels exert neurotoxic effects on the hippocampus and promote oxidative stress, leading to depression, neurodegeneration, and cognitive decline (43). On the other hand, one of the protective effects of regular exercise is lowering the serum cortisol level (44). Although these factors were not measured in this study, the observed improvements can be explained by these mechanisms.
The resting alpha and beta waves indicate relaxed and alert wakefulness, and the theta/alpha ratio is indicative of cognitive de cits. Decreased alpha wave power has been reported in AD (4,5), which is associated with an increase in the theta/alpha ratio. Therefore, the reduction of theta/alpha ratio in our study suggests that a combined training period with mental challenges for AD patients activates the mechanisms in the brain, which improve cognitive processing. This nding is in line with a previous study, which showed that ten weeks of limb exercise signi cantly increase the alpha and beta wave power in all brain areas of older adults with MCI (45); however, this study did not report the theta/alpha ratio.
Although the exact mechanisms of change in the brain wave ratio due to exercise training are unknown in AD, the alpha wave power seems to be correlated with higher cerebral blood ow in the brain areas, involved in attentional modulation (46). Alpha waves are generated mainly in the occipital and parietal lobes, as well as thalamocortical feedback loops, whereas beta waves mainly originate from the frontal and temporal lobes (47). The eye-closing part of our training protocol forced the individuals to focus on the auditory and proprioceptive data, originating from beta and alpha waves.
Moreover, the sensory data are distributed in different areas of the cortex through the thalamus.
Therefore, our intervention was highly effective in activating the brain parts involved in attention. In contrast, Gutmann et al. (2015) were reported no changes in alpha wave power after four weeks of moderate exercise training (14). It seems that methodological differences can explain these contradicting results. The subjects of the latter study were healthy young men, while the populations of our study were older AD adults. Overall, the ndings demonstrated that 12 weeks of training combined with mental challenge reduced the theta/alpha ratio by improving the neurophysiological mechanisms.
AD is associated with the loss of muscle mass and strength, reduced balance, and reduced cardiovascular tness, leading to inability to perform daily activities, loss of independence, and poor quality of life (1,3,48); therefore, our subjects' baseline tness level was very poor. Our ndings showed that three months of combined training caused substantial improvements in the performance indices.
Resistance exercises (dumbbells, TheraBand, and rubbers) led to increased strength and maintenance of muscle mass, balance exercises (walking on a beam board) and eyes-closed exercises improved proprioception, and consecutive exercises led to increased cardiovascular tness.
Improved balance in the present study is especially important, as balance and mobility impairments in AD patients are associated with the risk of falling and reduced quality of life. It is worth mentioning that the observed improvements after exercise training are not population-speci c, as comparable increments have been observed in the physical capacity of other populations after a short-term training program (49).
Improved tness components appear to be correlated with the ability to perform daily tasks and quality of life. This nding is in line with a previous study, which examined the effects of exercise training on functional capacity in AD patients (48).  (48). Also, moderate-to-large positive interactions were observed between changes in physical parameters and cognitive function. Moreover, there was a strong association between the change of muscle strength (especially handgrip) and MoCA. This nding was supported by a previous study, which showed a strong relationship between muscle atrophy and declined cognitive function (3). cardiorespiratory tness is associated with reduced brain atrophy in AD patients (35). Based on the ndings, exercise training can be an important adjunct to the pharmacological treatment of AD.

Limitations
We acknowledge that there are some limitations in this study. First, the posttest date coincided with the pandemic of COVID-19 in Iran, and we lost some of our participants. Second, due to the lack of full-time caregivers, transportation was di cult, and the workout time was not consistent; however, all participants completed 24 workout sessions. Third, we did not have access to quantitative EEG; therefore, we suggest using structural and functional brain imaging to assess quantitative changes in the brain structure and function in the future. Finally, we did not determine the period of time when these adaptations remained constant, which indicates the importance of follow-up after three, six, or even 12 months.

Conclusions
In conclusion, a 12-week combined training program, including resistance, balance, and cardiovascular exercises with closed-eyes stimulation, improved the performance capacity of patients with AD. Also, this intervention improved the brain health and activated neurophysiological mechanisms, which are associated with increased cognitive function and decreased theta/alpha ratio. Moreover, our ndings supported the hypothesis that cognitive functions are correlated with muscle strength-related physical tness in patients with AD. Helsinki. We obtained written informed consent from participants.

Consent for publication
Consent for publication is not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests Funding This research did not receive any speci c grant from funding agencies in the public, commercial, or notfor-pro t sectors.
Authors' contributions SA-S and EP conceived the study. EP, FM and BT conducted the experiments. SA-S and MB analyzed the study. SA-S, FM, and MB interpreted the data for the study. All authors made substantial contributions to the design of the work, drafted the work or revised it critically for important intellectual content, provided nal approval of the version to be published, and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All authors read and approved the nal manuscript  The absolute changes in the scores of the MoCA test following the 12-week intervention in both groups. TG; Training Group, CG; Control Group. *; signi cant difference between groups.