Exercise – What are the Benefits for the Brain?
By: Raphael Gabiazon
It is widely known that there are many physical health benefits that can be derived from engaging in physical activity. Exercise is associated with a longer health span and reduces the risk of various diseases and chronic conditions (1). However, recent advancements in technologies and scientific fields, particularly within neuroscience and kinesiology-related disciplines, have determined that there are benefits for cognition as well. Cognition is a fundamental human process as it allows the acquisition of knowledge and understanding through thought, experience, and the senses. It is used as an umbrella term to encompass many different cognitive functions, like attention and memory, that are essential for cognition (2). Exercise is strongly suggested to have advantages for cognition because it can help with sleep, age-related cognitive decline, and cognitive functions. This article will examine the research supporting the brain-based benefits of exercise.
An indirect benefit of enhancing cognition with exercise is through promoting better sleep. Having good sleep can affect cognitive functions which are typically utilized in all processes that require one to acquire and retain knowledge. For example, work productivity which is a measure of job performance is shown to be associated with cognitive functions (3). To demonstrate the importance of sleep and productivity, a Japanese study investigating the impact of sleep health on work showed that workers with short sleep durations had lower productivity (4). While having good sleep is the priority, it is not always guaranteed that it will occur. It is estimated that 10%–30% to even as high as 50%–60% of the population suffer from insomnia - a common sleep disorder that negatively affects sleep initiation, duration, consolidation, or quality – and is expected to increase in prevalence (5-7). Novel research would suggest that such concerning trends can be attenuated with exercise to facilitate sleep. A systematic review - which summarizes academic literature pertaining to a topic under investigation (8) – looked at 34 studies and found that most of the studies supported the use of exercise, regardless of the mode and intensity of activity, to improve sleep quality or duration (9). While the underlying mechanism of this effect remains unclear, one of the studies examining biomarkers included in the systematic review reported that a 12-week aerobic exercise intervention in sleep-disordered individuals reduced their levels of interleukin-1β (9, 10). Interleukin-1β is an inflammatory protein that is generally thought to enhance sleep but extreme elevations of it in the body may impair sleep (11, 12). Further research is needed to elucidate the exact mechanisms behind the positive effects of exercise on sleep. Although, from a behavioural perspective, there is strong evidence to recommend that exercise can be beneficial for sleep which can translate into improving cognitive functions for performing daily tasks, such as with productivity.
Exercise may also help with mitigating the negative consequences associated with age-related cognitive decline. Although the decline of certain cognitive functions is normal with aging (13), it may progress that could be detrimental to daily function. This process is widely observed during mild cognitive impairment (MCI) which is considered the transitional period between normal age-related cognitive decline and dementia – an overall reduction in memory and other cognitive functions severe enough to impair a person's ability to perform everyday activities (14, 15). While there are no medications that are proven to cure MCI, contemporary research has identified interventions that may help decrease the risk of further cognitive decline, particularly with exercise. This research interest for such interventions is driven by a globally aging population as it is expected that 1 in 6 people in the world will be aged 60 years or over that are at risk for MCI and subsequent cognitive decline (16, 17). A 12-month study contributing to these efforts from the University of British Columbia looked at 155 senior women and reported an increase in measures of cognitive function with resistance training compared to a non-resistance training group that was observed to have a decrease in their cognition (18). Similarly, a meta-analysis investigation – a research process that statistically analyzes studies examining the same question (19) – found that aerobic exercise in older adults with MCI significantly improved cognitive performance (20). It is important to note that the mechanisms underlying MCI and forms of dementia, like Alzheimer's disease (21), are still unknown. Given this, the exact mechanisms of how exercise exerts its cognitive benefits for MCI can only be postulated. One prevailing hypothesis is that resistance training may prevent cognitive decline by reducing levels of homocysteine and increasing levels of insulin-like growth factor 1 (IGF-1) (22 – 25). Increased levels of the compound homocysteine in the body are associated with impaired cognitive performance and Alzheimer's disease whereas the hormone IGF-1 is thought to improve cognitive performance (22, 26-28). The mechanisms in aerobic exercise are thought to be different as it is suggested that aerobic exercise can increase concentrations of brain-derived neurotrophic factor – a protein responsible for reorganizing neurons (the fundamental cells in the brain) that is related to learning and memory (29, 30). Based on the evidence provided, the mechanisms underlying the cognitive-related benefits of exercise are yet to be determined but would advocate the use of exercise to mitigate age-related cognitive decline.
As mentioned previously, the process of cognition is predicated on the performance of its functions such as attention and memory (2). Enhancing these would predict a better ability for acquiring knowledge and understanding through thought, experience, and the senses. Previous research has shown that exercise can enhance these cognitive functions. A study assessing the effects of aerobic exercise on measures of attention in individuals diagnosed with attention deficit hyperactivity disorder found it improved their attention as measured by faster reaction times and decreased errors during a cognitive test (31). While the mechanism that explains this effect is still unclear, it has been suggested that aerobic exercise can elicit greater increases in catecholamines – a type of neurohormone thought to be involved in attentional processes (32, 33). Another systematic review and meta-analysis study found both resistance training and aerobic exercise to have beneficial effects for working memory in older adults (34). These effects associated with resistance training may be due to reductions in homocysteine and increased IGF-1 as previously stated (22, 26-28). Regarding aerobic exercise, it is thought that the increased blood flow to relevant brain areas for memory during this exercise mode may be responsible in some populations (35). Taken together, exercise is beneficial for improving cognitive functions, but further research is needed to clarify its mechanisms.
In conclusion, recent research has demonstrated that exercise is beneficial for cognition through its indirect effect on sleep, mitigating age-related cognitive decline, and improving cognitive functions. Further research is warranted to determine the underlying mechanisms that drive these effects due to exercise. Regardless, any training mode whether it is through resistance or aerobic exercise can be advantageous for both physical and cognitive health.
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