You’re probably underestimating your muscles. In fact, almost everyone does. While everyone knows, for instance, that muscles are important for function—activities such as walking, climbing, and lifting—few appreciate just how important muscles are for feeling.
If you haven’t noticed this mood-muscle connection yourself, take heart; it is only a recent discovery. Surprisingly, the entire scientific community remained in the dark until approximately 2003 (1) when a team of Copenhagen-based researchers reported a remarkable discovery: Muscles at work secrete tiny chemical messengers called myokines that exert powerful effects on organ function, including brain function (2).
Through the actions of myokines, muscle tissue communicates directly with the brain about its activity, triggering a cascade of biological responses that improve memory, learning, and mood (see Figure 1 below). This newly discovered mechanism implies that a person engaging in physical activities that build and maintain healthy muscle tissue can expect to enjoy a range of cognitive and mental health benefits. Recent clinical trials show precisely this effect (3).
If anyone has ever accused you of being complicated, they really had no idea. Although you can’t tell by looking in the mirror, the body you see reflected is comprised of more than 100 trillion cells. Cells are tiny; if you put cells side-by-side in a police lineup, for example, about 200 of them would fit in a single millimeter.
But that’s just the beginning of the miracle we call you. Every cell in your body is a thriving civilization in itself, populated by hundreds of millions of proteins and other molecules, each possessing a work ethic that would put John Henry to shame. Scaled to our size, your cellular citizens fly around at the speed of fighter jets, each busying themselves completing hundreds or even thousands of life-preserving functions per second. They must maintain this frenzied pace without interruption for you to survive, totaling billions of trillions of precisely performed chemical activities every day.
If you somehow possess a superhuman imagination capable of conceiving of this cellular cacophony, you may entertain a question: what powers all this? Remarkably, the enormous energy required to run your cells ultimately comes from the oxygen you breathe and the food you consume.
The latter seems important to remember the next time you don’t feel like eating your vegetables. Digested to the smallest denominator, nutrients are converted by mitochondria—arguably the VIP citizens of your cells—into billions of adenosine triphosphate (ATP) molecules per minute. Although even an ordinary cell may house thousands of these energy-producing mitochondria, muscle cells are mitochondrial beehives, possessing tens or even hundreds of thousands to power their operations. Once made, ATP is feasted upon by your cells like exhausted runners devouring PowerBars at the finish line of the Boston Marathon.
Emerging almost impossibly from this molecular mayhem is you. Every thought, feeling, and action results from and depends on this unceasing cycle of energy demand and energy production. And if it isn’t apparent from this description, the better your cells function at the level of the little, the better you feel and function at the level of the large.
This brings us back to resistance training. Given the vital roles your muscles play in energy production and brain function, perhaps it is time to begin appreciating resistance training and muscle building as being useful for more than athletes and magazine models.
Using your muscles against resistance, for example, is far more effective for strengthening your bones than any calcium supplement (4). Regular muscle activity also improves insulin resistance (the cause of diabetes and many other metabolic conditions) better than any prescription medicine.
And now we know that stimulating muscle tissue with resistance training has emotional effects rivaling those of conventional antidepressants and psychotherapies (3). Recent neuroscience suggests that we evolved brains for one primary reason: to move (5). Counterintuitive to our traditional preoccupation with thinking, the primary function of the human brain is to coordinate complex movement (this is probably why we have brains while giant but stationary redwood trees do not).