Cognitive Function and the Risk of Dementia: The Influence of Physical Fitness and Exercise in Older Adults

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Cognitive impairment is one of the most common health problems among older adults and has become a major focus for healthcare providers due to the ageing of the global population. The prevalence of cognitive impairment has been estimated to be around 7% among older adults aged between 60 and 65 years, and is reported to increase to about 40% among older adults aged 80 years and over. Moreover, the most common mental and neurological disorders among older adults, which are Alzheimer’s disease (AD) and Parkinson’s disease (PD), are either defined by or associated with cognitive impairment. Cognitive impairment describes a continuum of signs ranging from subjective cognitive impairment (SCI) to mild cognitive impairment (MCI) and dementia. No cure for dementia currently exists, prompting increased efforts to understand the preclinical stages such as SCI and MCI as potential opportunities for new interventions. The current guidelines of the American Academy of Neurology (AAN) promote regular exercise for these individuals. However, only two studies underpin this recommendation of the AAN, and there is a clear need for studies with larger sample sizes, standardised neuropsychological testing methods, longer intervention periods and well-defined diagnostic criteria for MCI. A primary prevention strategy that delays the conversion to dementia by even two years would greatly reduce the total number of patients living with dementia, and result in important public health, economic and societal benefits. Therefore, this thesis explored the effects of exercise on cognition in individuals at high risk for dementia to determine if targeted exercise presents an optimal primary prevention strategy. In particular, this thesis focused on different modes of exercise, while also evaluating methods to monitor exercise intensity and physical activity. In addition, this thesis investigated the efficacy of electroencephalography (EEG) markers for cognitive decline in older adults. Physical activity, exercise capacity and cardiorespiratory fitness were compared between older adults (n= 121) across the spectrum of SCI and MCI, which was further divided into early (EMCI) and late MCI (LMCI), in study 1. Further, study 1 assessed the strength of the relationship between these physical characteristics and cognition. Participants with LMCI had significantly lower activity levels in both subjective (p=0.018) and objective (p=0.041) measurements. Additionally, participants with LMCI had a lower exercise capacity (p=0.041). Furthermore, a modest and positive relationship between cardiorespiratory fitness and cognition (r=0.25; p<0.05) was found. These findings suggest that physical activity and exercise capacity might present a marker for the risk of further cognitive decline. In order to determine the efficacy of EEG markers for cognitive decline, study 2 compared auditory evoked event-related potentials (ERPs) between participants with SCI (n = 13) and MCI (n = 13). In contrast to neuropsychological tests, in which participants with MCI performed significantly worse (Trail Making Test A: p=0.001, Cohen’s d=1.5; Trail Making Test B: p=0.030, Cohen’s d=0.94; verbal fluency letter: p=0.001, Cohen’s d=1.08; verbal fluency category: p=0.038, Cohen’s d=0.86), ERPs were similar between individuals with SCI and MCI. Based on these results, neuropsychological tests may be best to discriminate between individuals with SCI and MCI and should be used in future studies. Study 3 aimed to assess whether a target score on the subjective rating of perceived exertion (RPE) scale during light, moderate and vigorous exercise can be used to prescribe exercise intensity on an individual’s heart rate (HR)-RPE relationship in older adults (n=97, 75 ± 6 years) with MCI and SCI. Even though no differences between mean target and measured HR (mean difference 1.2 bpm) were observed, this study revealed some variance between the participants, with half of them demonstrating that the HR response differed by around 10 bpm when exercise was monitored with RPE alone. Therefore, this study concludes that the RPE should only be applied with caution and, if possible, with other measurements (e.g. HR monitors) to ensure that target intensity is reached. Study 4 investigated the validity of a commonly used wrist-worn activity monitor for tracking steps in older adults. 32 older adults (mean age 74.8 ± 5.9 years) walked for 200 meters wearing the activity monitor on the wrist of the non-dominant arm, while an operator counted steps manually. Lin’s concordance correlation coefficient revealed a strong correlation (rc=0.802) between the manually counted and objectively tracked steps, and accuracy was confirmed by creating Bland-Altman plots. Therefore, the results confirmed the validity of the activity monitor to assess steps accurately. Addressing the limitations of previous studies, the multicentre NeuroExercise study, which is study 5 of this thesis, aimed to investigate the effects of a 12-month structured exercise program (either aerobic exercise or stretching and toning exercises) on the progression of cognitive decline in people with MCI compared to a control group. This randomized controlled trial was conducted in three European countries and a total number of 183 individuals with amnestic MCI were randomized into three different groups. Primary ANCOVA analysis revealed no differences in cognition (Cohen’s d 0.11; mean difference 0.13; 95% CI -0.02-0.28) or quality of life (Cohen’s d 0.02; mean difference -1.89; 95% CI -4.59 – 1.00) between the exercise groups and the control group after 12 months. In contrast, cardiorespiratory fitness increased significantly in the exercise groups compared to the control group Cohen’s d 0.40, mean difference -1.76, 95% CI -3.39 – -0.10]. Secondary analyses showed centre specific and exercise-frequency related changes. Further, differences between the two exercise groups were found regarding physical fitness with the aerobic exercise group improving significantly more than the stretching and toning group. The improved physical fitness may be an important moderator for long term disease progression for individuals with MCI but did not have a positive effect on cognition after 12 months. It was the aim of study 6 to systematically review the effect of different exercise modes reported in randomized controlled trials on cognition in patients suffering from PD. This systematic review included a search of five electronic databases combining keywords from three categories, which were disease, exercise, and cognition. After screening abstract, title and full texts of 2,000 studies, 11 studies met the inclusion criteria. Study quality was modest (mean 6 ± 2, range 3-8/10). In 5 trials a significant between-group effect size (ES) was identified for tests of specific cognitive domains, including a positive effect of aerobic exercise on memory (ES = 2.42) and executive function (ES = 1.54), and of combined resistance and coordination exercise on global cognitive function (ES = 1.54). Two trials found a significant ES for coordination exercise (ES = 0.84–1.88), which led to improved executive function compared with that of non-exercising control subjects. All modes of exercise are associated with improved cognitive function in individuals with PD with a tendency towards aerobic exercise leading to greatest effects. Based on outcomes of this thesis, it cannot be concluded which form of exercise is best for individuals in the earliest stages of cognitive decline. Nevertheless, the results highlight the importance for considering this in future studies and the need for further direct comparisons of different exercise modes. These future studies should rely on valid methods to identify the target populations, and describe exercise interventions (e.g. exercise intensity) and their outcome parameters (e.g. steps) adequately – outcomes of this thesis will help future studies to do so. Even though a direct influence of supervised exercise on cognition was not demonstrated with this work, the relationship between cardiorespiratory fitness and cognition may indicate long-term benefits of an increased fitness for cognitively impaired individuals. As high physical fitness is a driving force for a socially integrated and fulfilling later life – especially in individuals at risk of cognitive decline – regular exercise should become routine in older adults with and without cognitive impairment.
Original languageEnglish
Place of PublicationKöln
PublisherDeutsche Sporthochschule Köln
Number of pages202
Publication statusPublished - 18.02.2020

ID: 5133907


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