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Title: Physical activity, cardiorespiratory fitness and cognition
Other Titles: Fysieke activiteit, cardiorespiratoire fitheid en cognitie
Authors: Angevaren, Maaike; S0166883
Issue Date: 29-Apr-2011
Abstract: The Western society is rapidly growing older which is reflected in the presence of complaints on cognition. Mild or normal age-related cognitive decline is associated with a negative impact on well being of the individual and the increased use of health care services. Research focuses on ways to improve quality of life and to reduce health care costs in older adults by addressing age-related cognitive decline. Several studies have consistently shown strong associations between physical activity and cognitive function. These studies indicate that people who are physically active either have better cognitive function or have a reduced risk for dementia. A number of hypotheses have been suggested in order to explain these associations between physical activity and cognition. This thesis addressed the idea that cardiorespiratory fitness is a mediator in the association between physical activity and cognitive function for healthy older people. If cardiorespiratory fitness is a mediator in the association, then physical activity should be of sufficient duration and intensity in order to enhance cardiorespiratory fitness. This thesis therefore encompasses studies on the specific parameters of physical activity which could counteract age-related decline. Chapter 2 describes the results of a Cochrane systematic review of randomised controlled trials (RCT’s) on physical activity programmes which enhance cardiorespiratory fitness and could result in cognitive changes in older, healthy people. This systematic review encompassed 11 RCT’s with 667 healthy participants of over the age of 55 years. The methodological quality of the included studies was classified as ’average’. Eight out of 11 studies assessed VO2peak and showed that an aerobic programme resulted in increased cardiorespiratory fitness (increased VO2peak of approximately 14%) for the intervention group whereas cardiorespiratory fitness did not change significantly in the control groups. Participants in the aerobic intervention groups showed better results on tests for motor function and auditory attention compared to participants who were in a ‘waiting list’ control groups. At the same time, aerobic physical activity programmes were beneficial for cognitive processing speed and visual attention, when compared with any other exercise programme (such as strength or flexibility based programmes). Aerobic physical activity programmes did not result in significant positive effects on the other incorporated cognitive domains such as executive function, perception, cognitive inhibition and memory functions in any of the comparisons. These results indicate that improved cardiorespiratory fitness is beneficial for some cognitive domains. The fact that the majority of the cognitive domains was not affected by the increased cardiorespiratory fitness prompts further research in the associations between physical activity, cardiorespiratory fitness and cognition. The results of a cross-sectional study in 1927 healthy participants of the Doetinchem cohort are described in chapter 3.This study aimed to give a partial insight in the question which parameters of physical activity might be associated with cognitive function. Physical activity was assessed with the European Prospective Investigation into Cancer and nutrition (EPIC) questionnaire. This questionnaire included questions on time (hours per week) spent on walking, bicycling, housekeeping, doing odd jobs and gardening and sports. All reported activities were given a specific Metabolic Equivalent (as described by Ainsworth) in order to calculate intensity. Cognitive function was assessed by means of a battery of tests that measured four specific cognitive domains, including cognitive processing speed, memory function, cognitive flexibility and overall cognitive function. The analyses indicated that average intensity (in METs per week) of physical activities was most strongly associated with cognitive processing speed, but there were also associations with memory function, cognitive flexibility and overall cognitive function. In addition, variation in physical activity (defined as the number of activities reported per week) was associated with all four cognitive domains. Duration of physical activities showed no associations with cognitive function in this cohort. The cross-sectional character of this study limits the conclusions that can be drawn from this study. Therefore, the associations between parameters of physical activity and cognitive function were examined in a longitudinal study (chapter 4). Physical activity patterns and cognitive function of the participants of the Doetinchem cohort were re-assessed in a 5-years follow-up study. Assessments of physical activity and cognitive function were similar to the assessments in the cross-sectional study (chapter 3). The longitudinal character of the study opened the opportunity to investigate whether changes in the duration or intensity of physical activities were associated with changes in cognition in a healthy middle-aged population. Analyses showed that changes in the total time spent on physical activities were not associated with changes in cognitive function over a 5-year period whereas an increase or smaller decline in average intensity was associated with a smaller age-related decline in cognitive processing speed. All significantly positive associations were limited to cognitive processing speed and were not found for the other cognitive domains (memory function, cognitive flexibility and overall cognitive function). The cross-sectional study in chapter 5 assessed the possible associations between measured VO2peak and cognitive function in 42 younger (18-25 years of age) and 34 older (55-62 years) employees of the Utrecht police force. This study adds to research in which only a few studies investigated the correlations of measured VO2peak and cognitive function in healthy adults where others used submaximal or estimated VO2peak data as a parameter of cardiorespiratory fitness. At the same time, this cross-sectional study examined whether particular domains of cognitive function might be more vulnerable to aging and whether certain domains of cognitive function would be more responsive to cardiovascular fitness. VO2peak was measured during graded bicycle ergometry until voluntary exhaustion. Cognition was assessed with a neuropsychological test battery and categorised into four domains; cognitive processing speed, motor function, visual and auditory attention. Univariate analysis showed that parameters of cardiorespiratory fitness (VO2peak in ml.min-1.kg-1, OUES or VO2 at VAT) were not significantly associated with any of the cognitive domains of interest in both age strata. However, bodyweight and BMI were significantly and negatively associated with cognitive processing speed in the older age stratum and the older group of men. Physical activity time nor average intensity of those activities nor parameters of cardiovascular risk showed any association with any of the four cognitive domains.The last chapter (chapter 6) contains the general discussion of this thesis. The main conclusion of this thesis is that cardiorespiratory fitness might give a partial explanation for the associations between physical activity and cognitive function. In addition, there are indications that intensity of physical activity rather than duration might be a more effective parameter in the prevention of age-related cognitive decline. This thesis predominantly describes associations between physical activity, physical fitness and cognitive processing speed. The studies in this thesis also showed that variation in activities and aspects of cardiovascular risk (weight and BMI) were associated with cognitive function. This suggests that associations between physical activity and cognitive function might be attributed to other mechanisms than a cardiorespiratory mechanism. Various researchers have suggested that not only cardiorespiratory fitness but also aspects of other hypotheses either slow age-related decline, prevent cognitive dysfunction or improve cognitive function in older people. It is proposed that the mere use of the brain will stimulate cognitive function and possibly promote structural changes to the brain (“use it or lose it” hypothesis). It should be noted that physical activity automatically implies stimulation of the brain and this thesis therefore, cannot rule out the influence of this mechanism. Besides questions regarding the relative influence of specific parameters of physical activity and the possible mediating role of cardiorespiratory fitness, future research must focus on the optimal period in terms of age, physical ability, physical fitness and cognitive decline in which potential preventative interventions should start. Physical activity might be more effective in some (yet to be fully identified) subgroups in the population. Although aspects of all hypotheses for the association between physical activity and cognitive function might still need to be examined in an unimodal design, studies ultimately should target the more multi factorial nature of age-related decline.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Research Group for Cardiovascular and Respiratory Rehabilitation

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