Earlier this month, the Surgeon General released a call to action: Americans need to walk more. The announcement, formally titled “Step It Up” (which does make you want to walk more, right?), notes that physical activity reduces the risk of a whole host of chronic diseases, plus boosts healthy aging and mental health.

Not that this is news to us—no doubt you’ve heard us extolling the virtues of exercise before. Walking regularly, or doing any form of moderate physical activity, is good for your heart, your memory, your blood sugar levels, your mood, and way, way more.

But you might not know why exercise improves your memory—it actually changes your brain. How, you ask? Well, that’s what we’re here for.

First, several studies have shown that exercise has profound effects on aging brains. Olga Kotelko, who began her athletic training at 77, went on to hold more than 30 world records in her age group. A study conducted when she was 93 and published last month (Kotelko died last year) found that, despite the late age at which she began training, her brain looked pretty different from other nonagenarians. Her white matter had fewer abnormalities, and her hippocampus (the region of the brain that is key for learning and memory) was bigger. In short, her brain was younger. Of course, this was an incredibly small sample size (of one), and the study’s authors hadn’t looked at Kotelko’s brain before she began training. But luckily, this isn’t the only research that shows exercise decreases the effects of aging on your brain!

A study of men and women aged 60 to 80 found those most physically active had more, and healthier, brain activity than those who exercised less. In particular, there was activity in the hippocampus (yup, that again—it’s pretty important!) and in connecting different parts of the brain. Another study of elderly men and women, this time between 70 and 89, suggests that exercise may have prevented cognitive decline.

But physical activity isn’t just good for the brains of the elderly. At the other end of the spectrum, researchers found that women who exercised for 20 minutes, three times a week while pregnant (starting in the second trimester) gave birth to infants with more active brains. This is no minor thing: such a boost in early brain development could impact kids their whole lives.

As for the rest of us in the middle of the age bell curve, exercise can reduce brain-based mood disorders like anxiety and depression, lower stress and anger, and help boost self-esteem, memory, and concentration.

One study found that just an hour of yoga increases levels of gamma-Aminobutyric (GABA), a neurotransmitter that protects against anxiety and depression, by 27 percent. And research out of Georgia found that riding an exercise bike for 50 minutes increased participants’ levels of endocannabinoids, the very receptors that allow marijuana to trigger a feel-good response. There is also the very logical fact that when you do cardio, your body pumps extra blood everywhere, including your brain—which helps it perform.

No matter your age, there are huge brain benefits to getting regular physical activity. So step it up, okay? We advise at least 150 minutes of moderate exercise, or 75 minutes of vigorous exercise, every week, or better yet 10,000 steps a day, 20 minutes of cardio three times a week, 20 minutes of resistance exercise and 40 jumps a day.

You can do it! Get a buddy and boost each other.