Fitness, aging and neurocognitive function

https://doi.org/10.1016/j.neurobiolaging.2005.09.009Get rights and content

Abstract

In this manuscript we provide a brief review of the recent literature that has examined the relationship among fitness training, cognition and brain. We began with a discussion of the non-human animal literature that has examined the relationship among these factors. Next we discuss recent epidemiological studies of the relationship between physical activity and fitness and cognition and age-related disease such as Alzheimer's dementia. We then discuss the results of randomized clinical trials of fitness training on human cognition. Finally, we conclude with a review of the nascent literature that has begun to employ neuroimaging techniques to examine fitness training effects on human brain. In general, the results are promising and suggest that fitness may serve a neuroprotective function for aging humans.

Introduction

The SPARK workshop focused on the relationship among obesity, diabetes, mood and cognition. Cleary, one important factor that relates to each of these constructs is physical activity and exercise. Lack of physical activity has been implicated in various health conditions including diabetes, cardiovascular disease, cancer, and osteoarthritis [14]. Increased physical activity reduces the risk associated with these diseases. Although less well-known, there is also an emerging body of literature that has found moderate to strong associations between physical activity and cognition, mood and human brain function, particularly in a group of individuals vulnerable to the loss of independence and cognitive decline, that is, older adults.

In the present paper we focus on the literature that has examined the relationship between physical activity and exercise on human cognition, brain structure and brain function. Specifically, we will examine the question of whether exercise can reduce age-related decline in cognition and decrease the risk for age-associated neurological disorders such as Alzheimer's disease. Rather than providing a thorough historical overview of this rapidly expanding literature we will concentrate on the expansion in our knowledge of the relationship among exercise, cognition and brain that has taken place over the past decade or so. To this end we will review both prospective and retrospective epidemiological studies as well as randomized clinical trials of exercise effects on human cognition, brain structure and brain function.

However, before focusing on the human literature we believe that it is important to provide a context for these studies, which largely derives from experiments with non-human animals. The examination of exercise effects in animals represents an expansion of a research program that has focused on the influence of complex environments on the brains of rodents. Given that living in complex environments entails increased physical as well as cognitive challenges, researchers began to decompose the influence of different aspects of these environments on brain structure and function. For example, Black et al. [5] compared the influence of wheel running with motor skills training on the brain function of older rats. Interestingly, the wheel running group developed a higher density of capillaries in the cerebellum than the animals trained on motor skills or a group of inactive controls. On the other hand, the animals in the motor skill group showed a larger increase in synapses in the cerebellum than the other two groups. Other studies have shown similar effects of treadmill exercise on the vasculature in the motor cortex of middle aged monkeys [19].

Exercise training in aging animals has also been shown to increase levels of key neurochemicals that improve plasticity and neuronal survival, such as brain-derived neurotrophin factor (BDNF) and insulin-like growth factor 1 (IGF-1), serotonin, as well as reduced corticosteroid levels [4], [6], [12]. There have also been a number of recent demonstrations of enhanced learning and memory and neurogenesis with exercise training [21], [22]. Finally, voluntary exercise has been found to decrease amyloid load in a transgenic mouse model of Alzheimer's disease [2]. Such data provide a promising context in which to examine the influence of fitness training on human cognition, brain structure and function.

Section snippets

Epidemiological studies of fitness effects on human cognition

A number of recent prospective studies with fairly large numbers of older participants have examined the relationship between measures of physical activity and cognition. For example, Yaffe et al. [23] reported a study of 5925 high functioning community dwelling women (>65 years of age), who were characterized in terms of the number of blocks that they walked per week. The central question was whether higher levels of activity, particularly the number of blocks walked per week, would serve a

Fitness training effects on cognition and brain

Human fitness training studies conducted over the past several decades have produced a varied pattern of results. Some studies find a positive relationship between fitness training and cognition while other studies fail to observe such a relationship. There are a multitude of potential reasons for this mixed pattern of results including the use of different physical training and assessment protocols, different cognitive assessments, and generally small sample sizes. To increase the power to

Conclusions and future directions

The human behavioral and brain data discussed above suggest that fitness training holds great promise as a neuroprotective intervention during the course of the adult lifespan. The human data also are compatible with non-human animal studies of fitness training effects on performance, brain function, and brain structure.

However, there clearly are important questions that remain to be answered. For example, it is still unclear as to the dose response relationship among mode, duration and

Conflict of interest

None of the authors have any conflict of interest to report. The study was conducted consistent with ethical principles.

Acknowledgements

We would like to thank the National Institute on Aging (AG25667 and AG25032) and the Institute for the Study of Aging for their support of our research.

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