How exercise benefits the brain

As New Year resolutions become distant memories, my motivation to exercise is at risk of tapering off...

My mind may or may not be reassessing some goals, as it weighs the benefit-to-cost ratio of my recent exercise behaviour. On one side of the equation, I know exercise is good for my health, but, on the other side of the equation, I have a growing suspicion that missing out on social events, lie-ins, and Netflix may not be such a good thing. Now seems like a good time to weigh in on my thought process with a few reminders, which may be useful to others who are following a similar thought pattern.

Killing 5.3 million people...
Exercise is good for our health. Actually, we don't need to be reminded about this, we already know this statement to be true. However, we often don't think about the reverse of this statement; how dangerous is physical inactivity to our health? One possible answer is to consider the extreme, that physical inactivity has been estimated to kill 5.3 million people worldwide in one year [1]. Physical inactivity was defined in this estimate as doing less than 150 minutes of moderate-intensity exercise per week. Despite this estimate being based off imperfect measurements and calculations, the death toll takes into account the negative impact physical inactivity can have across multiple aspects of health, all of which may reduce our lifespan.

This hints that movement is integral to human health. However, the broad-brush concept that exercise is good for us is not new. In fact, exercise is good for multiple aspects of health, and we can develop a greater appreciation for exercise by understanding its numerous benefits. This is especially true for those interested in brain health, as the connection between brain function and movement may not be immediately apparent. Brain function should not be considered in isolation. In fact, it can be considered to exist as part of a triad (Figure 1) and thus linked to both movement and metabolism (the way our bodies store and use energy).

Researchers think the connections between movement, metabolism, and brain function extend back to the time of our hunter-gather ancestors, who not only had tooutrunbut alsoout-plantheir peers in the hunt for food [2]. Through successive generations, the links between these three components of survival were reinforced to forge what is a strong prerequisite for our health today. In essence, by not fulfilling our requirement to be physically active, we risk a knock-on effect to other components of health that may ultimately cause us harm.

Brain function is one of these components which is important for independence, productivity and quality of life. Brain function is something which can also decline with age, and this decline can ultimately lead to significant loss of functionality. Dementia is an umbrella term which represents conditions characterised by cognitive decline past a certain threshold. Some estimates place the process of cognitive decline to begin in healthy educated adults as early as in their 20s and 30s [3]. However physical activity is widely believed to be able to maintain brain function and is, therefore, integral to the prevention of ageing-associated dementia [4].

Exercise and brains
The benefits of exercise on the brain include changes to the structure and function of the brain which ultimately protect us from cognitive decline. Emerging technologies which image the brain show that important brain regions physically shrink with age, adding weight to our understanding of cognitive decline. Exercise has been shown to protect the brain from this type of shrinking and is even able to increase the volume of brain regions important for learning and memory [5]. In this light, at every stage of our lives, we should look for ways to introduce exercise into our day.

然而,锻炼可能只是答案的一部分nd what we do outside the time we spend exercising may also be important. It turns out that making the choice to sit for large parts of our day is a health risk, even for those who regularly exercise. A recent high-profile study estimated that to offset the increased risk of death associated with sitting for 8+ hours per day, that 60-75+ minutes per day of moderate intensity exercise was required [6]. For many, doing this much exercise every day is impractical. But, in addition to exercise, by reducing and breaking up our sitting time with light intensity activities throughout the day, we may be able to further offset some of this risk. However, one question that remains unanswered is whether reducing and breaking up sitting time has a role in slowing the cognitive decline associated with ageing? A recent systematic review, which compiled 8 separate studies on this topic, suggested that higher sedentary behaviour is associated with lower cognitive performance [7]. However, across these studies, methods for measuring sedentary behaviour and cognitive function were both varied and imperfect, meaning the jury is still out on this question.

Movement engineered out of our lives
To bring it back to the triad, we can focus on the movement component as being an important agent of change. The case could be made that with technological advancement, movement has been engineered out of our lives and this change has had negative consequences not just for our bodies but also our brains. On a positive note, this also implies that by moving more we can improve our body and brain health. Moreover, recent research suggests that this movement may not solely be restricted to planned, structured exercise; like making it to the gym 5 times a week. But could also involve reducing and breaking up our sitting time with frequent light intensity activities. With accumulating evidence, we can take heart that it appears movement of any kind is beneficial. In addition, we can also take heart that discovery of new ways in which movement is beneficial to health is also accumulating. Brain health is a great example of this, and it is what motivates me to stay physically active.

To solidify an appreciation for the link between movement and brain function we can look to the work of neuroscientist Rodolfo Llinás, who eloquently explained the idea that the evolution of the body and mind is connected to movement. In his 2002 book, I of the Vortex: From Neurons to Self, Llinás explains the theory that our nervous system evolved to internalise the properties of the outside world, then to transform those internalisations into movement patterns to increase our chances of finding food. To take a quote from his book which sums up this concept, Llinás writes, "That which we call thinking is the evolutionary internalisation of movement."