Insufficient physical activity is a problem in the modern world. We know it contributes to things like issues with our metabolic health and cardiovascular systems, but it also contributes to mental health issues, like depression. This is a clear example of the inseparable relationship between exercise and cognitive function. Indeed, the amount and type of physical activity that you include in your life influences how well you think and learn.

This evidence points to the idea that adequate physical activity provides an important input for the proper functioning of our brain. In fact, exercise not only appears to have an important role in mental health and cognition, but it also appears to protect the brain from diseases (e.g., Parkinson’s disease, Alzheimer’s dementia, and stroke). A lot of research on how adequate physical activity helps the brain has been published in the last 10 years. I will describe some of the key findings in this new blog series. In this article, I cover blood flow.

I’m not done with my series on better aging (1 – introduction, 2 – calorie restriction, 3 – protein restriction, – alcohol, 5 – metformin) quite yet, so these series will overlap for a period of time. But since I’m doing another project on exercise and cognition for organizational and employee performance, I decided to write about it here on the blog.

 

Exercise and cognitive function: how does exercise intensity affect blood flow to the brain?

The body needs a good supply of blood to receive oxygen, nutrients and energy substrates, and to remove waste. When you move your body, you increase the energy demands of the muscles being used for movement. In order the shuttle blood to the right place, vessels release nitric oxide – formerly known as endothelial-derived relaxing factor – to open nearby vessels and allow blood to flow to the areas where it’s needed.

When you exercise regularly and continue to increase blood to the extremities, two important acclimatizations happen: 1) the same nitric oxide that opens vessels also stimulates new vessel formation, and 2) it increases total blood volume by about 15% (sedentary to trained). Both of these acclimatizations better enable you to get blood to high-usage areas, and for that matter, to all other areas of the body that require blood. The brain is one of those areas.

In contrast to other organs, it was traditionally thought that total brain blood flow was not changed during physical activity. Research in the last 10 years, however, changed this perspective. We now understand that the increased neuronal and metabolic activity of the brain during exercise drive increases in blood flow to it. Exercise that is about 60% of maximal effort – so equivalent to a brisk walk to a jog – elevate brain blood flow, which then declines towards baseline flow levels as the exercise gets more intense (mediated by a lowered partial pressure of carbon dioxide gas in the arteries which causes the vessels to narrow in diameter letting less blood through). In fact, this decreased brain blood flow at high exercise intensities reduces the amount of oxygen to the brain, which is thought to be one of the mechanisms by which we fatigue. It would stand to reason that lower intensity exercise should enhance cognition while higher intensity efforts would impede it. This reminds me of a quote from one of my favorite books, Thinking Fast and Slow by Nobel Prize winner, Daniel Kahneman.

“One of my great pleasures there [in Berkeley, California] is a daily four-mile walk on a marked path in the hills, with a fine view of San Francisco Bay. I usually keep track of my time and have learned a fair amount about effort from doing so. I have found a speed, about 17 minutes for a mile, which I experience as a stroll. I certainly exert physical effort and burn more calories at that speed than if I sat in a recliner, but I experience no strain, no conflict, and no need to push myself. I am also able to think and work while walking at that rate. Indeed…. I did the best thinking of my life on leisurely walks with Amos. Accelerating beyond my strolling speed completely changes the experience of walking, because the transition to a faster walk brings about a sharp deterioration in my ability to think coherently. As I speed up, my attention is drawn with increasing frequency to the experience of walking and to the deliberate maintenance of the faster pace. My ability to bring a train of thought to a conclusion is impaired accordingly. At the highest speed I can sustain on the hills, about 14 minutes for a addition to the physical effort of moving my body rapidly along the path, a mental effort of self-control is needed to resist the urge to slow down. Self-control and deliberate thought apparently draw on the same limited budget of effort.”

It’s likely that some of the cognitive effects described by Kahneman are in part mediated by the blood flow vs. intensity effects described above. Now, it’s not that you can’t think well when you exert yourself more intensely. It’s that the demands of the exercise start to consume more of your focus making it harder to direct the increased energy supply through enhanced blood flow to deep thinking and complex problems even before you start to experience greater-intensity induced oxygen decline. Like Kahneman, I have found that long hikes do wonders for solving complex challenges related to work and life. That recognition made me wonder, “can I induce this state more regularly while at work?”

 

60% max effort exercise (like jogging) elevates brain blood flow, which declines with higher intensities Click To Tweet

 

Exercise and cognitive function: the importance of exercise intensity

The information above is one of the reasons I have always promoted a mixed intensity, mixed modality movement practice as a part of our Enduring Mover philosophy. Mixed intensity means that you are doing physical exertions all along the intensity spectrum – for example, exercises equivalent to jogging to sprinting. Mixed-modality training means you include a variety of movement styles in your regular activity routine to promote mobility, strength, and stamina.

It is important to note this because our society has systematically removed the need for physical activity in life (think cars and desks). Most of us were born into a world that doesn’t require much of it. Yet, most people believe physical activity is good for health, and because it’s inconvenient,  we have sought ways to minimize the time requirement for it. In doing so, it’s been found that high-intensity training is, indeed, very efficient at promoting health outcomes. For example, this meta-analysis just published by Jelleyman and colleagues showed that:

“high-intensity training is a suitable alternative to continuous exercise training in the promotion of metabolic health and weight loss, particularly in those with Type 2 diabetes or metabolic syndrome.”

This is a good thing: valuable health outcomes with less time. As such, high-intensity exercise styles are increasingly preferred and endorsed. This alone is not a problem. It’s problematic when lower intensity exertions are marginalized by the media making people feel there is no merit to them. I’m all in favor of finding efficient solutions to inactivity, and I do include high-intensity training in my weekly exercise practice.

Currently, for intense activity, I do body weight training (push ups, pull ups, bodyweight squats, etc) four to six times a week (via InTUNE Training), and indoor cycling classes (Soul Cycle and Peloton) and / or outdoor bike riding one to three times a week. On a side note, in my mind, my gifted Soul Cycle instructor, Heather Anderson, has transcended the role of trainer and has sublimated to the status of a Greek Goddess-level health muse. I will be sure to have her on the nascent humanOS Radio podcast so she and I can discuss her unique ability to motivate people to do high-intensity exercise joyfully.

So intense exercise is useful and efficient at promoting health outcomes. But, I also walk, jog, hike, or even dance 10K steps per day, and mix bursts of activity into my day. I do this to increase blood flow to my brain and to stimulate better cognition across the day. So don’t just sit then burst. Rather, fill your day with lower intensity movement to keep yourself as sharp as possible.

So far I have only discussed how exercise intensity impacts blood flow to the brain.  I have not discussed any associations to physical activity and specific cognitive processes. But this post is getting long so I will end with this teaser: One area of the brain that has been shown to receive heightened blood flow during exercise is the hippocampus, which is a brain structure critical to memory formation. In a future post in this series, I’m going to talk about the effects of regular exercise to see if there are benefits on memory. But in the next article, I’ll discuss the effects of exercise on various brain growth factors that help our neurons be healthy and connect to one another, which is critical for learning and brain health.

 

Photo credit for Daniel Kahneman: http://www.nobelprize.org/nobel_prizes/economic-sciences/laureates/2002/kahneman-facts.html