Life After Full-time Work Blog

Learn about preparing for life after full-time work through posts from Don's upcoming book.

#160 Think Of Your Brain Like A Muscle

… even though it isn’t. (It’s an organ.)


Before getting to the subject of this blog post,  I’m very happy to tell you that an interview with me has been published as a podcast on That Annuity Show. The hosts, Paul Tyler and Ramsey Smith, are knowledgeable and kind, and I’m delighted to join a long and distinguished list of interviewees.


Why think of your brain like a muscle? Because we’re much more conscious of our muscles than of our organs, and we understand our muscles instinctively, but not our organs. So, since there are ways in which the brain acts like a muscle, it’s much easier to understand the brain if you think of it (in that regard) as being a muscle.

I’ll explain three things, in connection with our muscles and our brain: what they do (how they help us function); their growth; and their decline.


What does a muscle do? Muscles are responsible for movement. They enable us to exercise and be physically active and strong.

They grow when we challenge them with resistance. They waste away not only with certain medical conditions, but also when we’re inactive for long periods, and as we age. After age 30, it’s natural to lose 3% to 5% of muscle mass every 10 years. And as our strength declines, it affects our ability to perform daily tasks and increases our risk of falling, which can have further negative health consequences.

What does the brain do? This requires more explanation than for muscles, because we’re less familiar with the workings of the brain.

The brain controls our thoughts and awareness and feelings, our memories and our speech. Along with the spinal cord, it controls our central nervous system. With our brains, we make sense of things. And the particularly advanced nature of the human brain distinguishes us from other species.

Our brain needs a lot of support. Even though it’s only 2% of our body weight, it uses 20% of the oxygen and blood in our bodies – enough to fill a bottle of wine every minute. I’ve heard it expressed as the brain being the heart’s best customer.

It used to be thought that, most of the time, we used only a small part of our brain. That’s now known to be false. We’re simply not conscious of our brain functions. Most of the time, most of our brain is working. But much of the activity is at a sub-conscious level, such as when we sleep.

The brain consists of many cells – about 100 billion of them. (That’s 1 followed by 11 zeroes!) They don’t touch one another: they have little gaps between them, known as synapses. And they send electrical and chemical currents across the gaps. These transmissions create circuits, depending partly on our genetic make-up and partly on our responses to the environment. There are trillions of these circuits, and there can be as many as 100,000 connections in each circuit. Mind-blowing!

We actually have two types of brain cells: neurons and glial cells. Think of the glial cells as supporting the neurons. So we’ll focus on the neurons.


Now to brain growth. Most of our neurons are there from birth or form shortly after. But important parts of the brain expand in infancy and adolescence too. And in fact we form new neurons (the jargon term is neurogenesis) and new pathways all through our life. Most people don’t know that when they practice and learn new things, parts of their brain change and get larger. This is true even for adults.

That’s just as well, because our brain cells naturally shrink with age, causing a gradual decline in brain function, particularly after age 30, and the rate of decline increases after age 60. That’s why some functions, like learning and memory, can gradually deteriorate.

Perhaps you can now see some similarities between the brain and muscles.

And I’m going to explain why, for both brain and muscles, it’s important to “use it or lose it; but don’t abuse it.”


A very important aspect is that both the brain and our muscles get stronger as we use them. And since both are fundamental to our lives and both decline naturally with age, using them and strengthening them become extremely important. That’s why exercise and sleep are fundamental components of a long and healthy physical and mental life.

Exercise (particularly resistance training) helps to build muscles. If you challenge your muscles to deal with gradually higher levels of resistance or weight, you actually first damage the muscle fibers. In healing, they fuse together and, in so doing, increase in size and strength. So obviously, don’t overdo the exercise to the point of destroying, rather than just damaging, muscle fiber.

Sleep provides the time for our muscles to recover and repair and thereby strengthen themselves. Sleep is also when growth hormone is produced, particularly during the time when delta waves form; this aids bone and muscle strength.

Surprisingly, physical exercise is also the best way to make lots of new neurons. Aerobic activity is very effective: not just things like running and swimming – add sex to that list. Exercise also greatly helps our ongoing mental health. This happens via improved blood flow to the brain, particularly to the brain’s limbic system, which controls our emotional responses, like motivation, mood and stress – that’s why these aspects of our mental health improve with regular exercise.

And now it won’t surprise you to learn that sleep assists neurogenesis too. But it isn’t just sleep that helps. What we need is for these new neurons to join brain networks, and also to form new networks, a process which then protects them by making them part of a collective. This is helped by enriching your environment and challenging your brain when you experience new things. And success in starting something new feeds on itself – practice makes you better – because the more you challenge yourself, the more your new cells grow and the stronger the pathways you develop, which in turn makes it easier for you to continue your learning.

Add diet and mindfulness to the list of things that help grow new neurons and neural networks. But I’ll explain mindfulness in another blog post.


I mentioned earlier that after age 30 both our muscles and our brain start to shrink naturally (and that’s why, to counter it, we should exercise brain and muscles, without overdoing it). Now let’s consider that natural shrinkage.

Muscle atrophy is called sarcopenia. If you don’t use your muscles, your body will eventually break them down, to save the energy that goes into maintaining them. Lack of use therefore accelerates the aging effect, as does poor diet as well as some medical and genetic conditions. That’s what we’re trying here to avoid, along with the negative health and balance conditions that accompany it.

Brain atrophy doesn’t seem to have a specific medical term attached to it, but it’s caused by some injuries, diseases and infections, as well as occurring naturally. And, depending on the part of the brain that is most affected, it can result in dementia, seizures and problems with speaking and understanding language. That’s why we’re trying to slow down the natural process. I found it interesting to discover that when we lose neural cells and connections, the latest ones are lost first. In fact that explains why, as we lose our memories, the earliest memories are the ones we retain the longest. Again, this is why, with neurogenesis, “use it or lose it” is such an important instruction.



In some ways, the brain is like a muscle. Overall, the connection between exercise and sleep, on the one hand, and mental and physical health, on the other hand, is very strong. They help to sustain and build our brain and our muscles, and also slow down the natural rate of decline. So, with both the brain and our muscles, the mantra should be: use it or lose it; but don’t abuse it.



I have written about retirement planning before and some of that material also relates to topics or issues that are being discussed here. Where relevant I draw on material from three sources: The Retirement Plan Solution (co-authored with Bob Collie and Matt Smith, published by John Wiley & Sons, Inc., 2009), my foreword to Someday Rich (by Timothy Noonan and Matt Smith, also published by Wiley, 2012), and my occasional column The Art of Investment in the FT Money supplement of The Financial Times, published in the UK. I am grateful to the other authors and to The Financial Times for permission to use the material here.

4 Responses to “#160 Think Of Your Brain Like A Muscle”

  1. Ted Harris says:

    Having the right genes helps. Off hand I’m thinking of Charlie Munger and Henry Kissinger, both 98 and still working.

    For those interested in further reading on how remarkable the brain can be, even when damaged, read two great books by Dr Norman Doidge: “The Brain That Changes Itself” and “The Brain’s Way of Healing”.

  2. Jeremy Brereton says:

    Thank you for taking us on another important ‘walk’ on our Life Two journey. As ever, you have summarised this complex subject clearly and succinctly. Do you have any exercises for us on this subject (as in your Life Two book).
    Many thanks

    • Don Ezra says:

      Thanks, Jeremy. Nothing specific about brain exercises at the moment. I’m researching them, and they come into play in connection with mindfulness too — which I’ll write up some time.

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