Effect of physical activity on the cognitive performance of middle aged New Zealand workers
Thomas, Judith Ann
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Given the projected ageing of the population over the next twenty years, age-related cognitive decline will become a significant contributor to New Zealand’s burden of disease, unless factors which provide some protection against these changes are identified. Proponents of the cognitive reserve model postulate that cognitive ageing is highly individual and that healthy behaviours can ameliorate age-related declines in cognitive performance through building of neural reserve. Physical activity has been purported to enhance cognitive performance. However, the literature focuses largely on older populations which does not capture the potential protective effects of physical activity throughout adulthood. The majority of these studies are correlative and do not provide sufficient detail on the type of physical activity which is most beneficial. Given the vast number of neuropsychological tests employed across cognitive domains, good quality research is needed which employs reliable and valid instruments. Objectives: The primary aim was to determine whether cognitive performance in middle age could be enhanced by either of two contrasting exercise interventions compared to no exercise. The secondary aim was to investigate whether cardiovascular function would moderate changes in cognitive performance. Methods: A pilot study was employed to test a high intensity exercycle protocol for its feasibility and its effectiveness in improving cardiovascular function. Five females aged 45-61 years participated in a six-week intervention. Cardiovascular function was assessed prior to and upon completion of the program. A postintervention survey was used to gather information on the perceived advantages of the program and on recommendations for improvement. For the main study, sixty-two healthy but low-active individuals (aged 40-64 y) participated in one of three 16-week programs: walking, exercycling or control. Episodic memory (verbal recall) was assessed using the Wechsler Memory Scale-III-A Logical Memory and Family Pictures subtests. Executive function (set shifting) was assessed by the Wisconsin Card Sorting Test. Cardiovascular variables included: body mass index, systolic and diastolic blood pressure, fasting blood cholesterol profiles and glucose. Pretest to posttest changes in cognitive performance were compared among the intervention groups, with respect to participant cardiovascular function and risk level. Results: Results from the pilot study supported the feasibility of the exercycle program, indicating that participants enjoyed the program’s activity and social support aspects. Participant recommendations for program development included: greater choice of music, more convenient session times and more motivational tools. Cardiovascular function variables did not significantly improve over the short intervention period. Results from the main study did not indicate any effect of exercise on memory. However, compared to low cardiovascular risk participants, those of high risk improved immediate story recall to a greater extent. Decreases in systolic blood pressure were significantly correlated with improvement in immediate story recall, with correlations stronger for those of high cardiovascular risk. Although executive function was not differentially affected by a specific exercise program, involvement in any physical activity resulted in greater improvement in set shifting compared to controls. Cardiovascular function did not significantly modify changes in executive function. Conclusions: Engagement in a physical activity program of any type can improve set shifting in middle age. However, memory-dependent processes such as verbal recall depend more on the improvement in cardiovascular function, particularly for individuals of high risk. Multi-faceted programs focused on cardiovascular health may have important flow-on effects for maintaining the memory function of the ageing population.