Content taken from A Little Theology of Exercise by David Mathis, ©2025. Used by permission of Crossway, a publishing ministry of Good News Publishers.

On weekdays I spend most of my work time in front of a screen. As a pastor who teaches, writes, and edits for a living, I am not paid to lift, dig, carry, push, or even move (other than my fingers). My job is not physically demanding, though it is often emotionally taxing enough that I’d be happy to swap in some manual labor.

Not that I want to do hard physical work full time! I enjoy mental labor—reading, researching, thinking, brainstorming, writing, and editing. Yet I’ve learned that I cannot undertake those sedentary tasks at my best when my whole life is sedentary. My brain is wonderfully served by bodily movement.

As I’ve aged, I’ve sensed more tangibly how much better I feel after exercise and with a pattern of exercise in my life. In particular, I seem to think clearer, more effortlessly, more creatively, and with more focus and mental stamina. Overall, when exercising regularly, I sense that I have more energy not only for further exertion but also for thinking and working hard with my mind. I’ve heard other people say the same.

But is this just in our heads, or is there any known biological basis for it? Can we get some clarity about this perceived mental clarity?

A few years ago, I stumbled upon a book by a professor of psychiatry at Harvard Medical School named John Ratey. He spent most of his career focusing on ADHD and co-wrote some important works in the field. As a doctor, former amateur athlete, and runner, he had noticed over the years how exercise seemed to serve as amazing “medicine” for his patients. Eventually, he put his findings together in the 2008 book Spark: The Revolutionary New Science of Exercise and the Brain.

Now, if it sounds too good to be true—that exercise demonstrably improves brain function—remember what the prescription is here: exercise. Apparently, many people just want to take pills. Few want to take exercise. The prescription may be simple, but it’s not easy.

Here’s how Ratey opens the book:

We all know that exercise makes us feel better, but most of us have no idea why. We assume it’s because we’re burning off stress or reducing muscle tension or boosting endorphins, and we leave it at that. But the real reason we feel so good when we get our blood pumping is that it makes the brain function at its best, and in my view, this benefit of physical activity is far more important—and fascinating—than what it does for the body. Building muscles and conditioning the heart and lungs are essentially side effects. I often tell my patients that the point of exercise is to build and condition the brain.

How many of us have started some new exercise regimen because we felt overweight and out of shape or because we were confronted with metrics from a doctor? We wanted to reduce our cholesterol, lower our weight, live longer, or look better. All these benefits, motivating as they may be for millions, are at best side effects of regular exercise.

The point of exercise, in our sedentary modern lives, is building and conditioning our brains. Ratey continues, “To keep our brains at peak performance, our bodies need to work hard. . . . The brain responds like muscles do, growing with use, withering with inactivity”—and movement activates the brain. Then Ratey explains how it is that exercise improves learning—which matters to us as Christians seeking to love our Lord with heart, soul, strength, and mind.

As Christians, we call ourselves disciples, which means learners. Chris­tian­ity is a teaching movement, with instruction from the Torah, the Psalms, the prophets, the apostles, and Christ himself—the consummate teacher. Correspondingly, Chris­tian­ity is also a learning movement—in Christ we are lifelong learners. Brain function matters greatly to me not only as a pastor and teacher but as a Christian. So here’s “how exercise improves learning on three levels”: “First, it optimizes your mind-set to improve alertness, attention, and motivation; second, it prepares and encourages nerve cells to bind to one another, which is the cellular basis for logging in new information; and third, it spurs the development of new nerve cells.”

First, mind-set is no small issue today in the age of digital distraction and dullness. If I can be more alert to the world, to others, and to mentally challenging texts and sequences of thought, then I’m interested. Alertness is a deeply Christian pursuit (and a key reason many of us make use of caffeine). And in a day when so many are woefully and tragically distracted by unceasing devices and the mirage of multitasking, we could hardly list many more valuable benefits than improved attention.

Second and third, modest exertion of the body and persistence in it (say twenty-plus minutes) produces a cascade of good effects in the brain and body, from neurogenesis (actually growing new brain cells) down to the nitty-gritty strengthening of, in Ratey’s words, “the cellular basis for logging in new information.”

So, active bodies improve learning. Exercise helps to develop new brain cells, encourages the binding of those cells, and improves our focus and eagerness to learn. Christians, of all people, would not want such discoveries to be lost on us.

Now, it’s one thing to hear that moderate bodily exertion improves learning; it’s another to hear specifically about three ways it does this; and it’s another still to learn how it happens. For me, specifics like these motivate me even further, especially in those moments when I feel happy to stay sedentary and not take the uncomfortable step of overcoming the inertia of inactivity. How does it work? According to Ratey,

Going for a run is like taking a little bit of Prozac and a little bit of Ritalin because, like the drugs, exercise elevates…neurotransmitters. It’s a handy metaphor to get the point across, but the deeper explanation is that exercise balances neurotransmitters—along with the rest of the neurochemicals in the brain.

And we can go one step further:

BDNF [Brain Deprived Neurotrophic Factor, which Ratey calls “Miracle Grow” for the brain] gathers in reserve pools near the synapses and is unleashed when we get our blood pumping. In the process, a number of hormones from the body are called into action to help…During exercise, these factors push through the blood-brain barrier, a web of capillaries with tightly packed cells that screen out bulky intruders such as bacteria… Once inside the brain, these factors work with BDNF to crank up the molecular machinery of learning. They are also produced within the brain and promote stem-cell division, especially during exercise…The body was designed to be pushed, and in pushing our bodies we push our brains too.

Make no mistake, the above observations are not explicitly Christian. At their best, they are in the realm of natural revelation. How, then, might we reflect as Christians on these fairly recent findings in neurology and their relationship to our God and his calling on us in Christ?

Train the Body, Serve the Soul

“Bodily training is of some value,” says Paul, even as he emphasizes that “godliness is of value in every way, as it holds promise for the present life and also for the life to come” (1 Tim. 4:8). Some value is a carefully crafted phrase. Doubtless, many in Paul’s own day, as in ours, held the human body in too high regard. They needed to hear that bodily training is of some value but not too much. Yet others—perhaps especially Christians who had been awakened to the far greater value of holiness and life in the Spirit—needed to open their minds afresh to Paul’s affirmation of any value at all.

Even as we affirm and seek to celebrate the far greater value of Christlikeness, we might ask ourselves, practically, What tangible value do I see and act on in bodily training? And for those of us who do find value in exercise, we might also ask, Do I simply want to lose fat, look better, and live longer in this fallen world? Or might I find a value in bodily training that serves godliness and (among other things) my brain function in the service of Christ?

Put another way, might my Christian life—my increasing godliness and Christlikeness—be compromised because I’ve failed to love my Lord with all my mind? In the words of John Piper, have I failed to “embrace serious thinking as a means of knowing and loving God and people”?…I am waving a little flag for you to consider, perhaps for the first time: how modest, regular exercise might be a means of building and conditioning your brain for serious thinking by improving mental energy, focus, clarity, and stamina. That is, serious thinking in the service of Christ and Christian joy.

In B. B. War­field’s famous essay “Religious Life of Theological Students,” he poses what seems to be an either-or dilemma for some: Should I study or should I pray? War­field answers with a memorable both-and: How about “ten hours over your books, on your knees”? Today, we might only add, “And how about after twenty minutes of modest exercise?”