No pain, no gain. So goes the familiar expression we invoke to justify the lingering aches that can result from exercising. However, if you need extra motivation, consider that the gains are not just measurable physically, but mentally as well. Kelly McGonigal is a psychologist, movement instructor, Stanford lecturer and bestselling author whose work explores the relationship between physical activity and a healthier state of mind.

How does your work as a psychologist intersect with your work as an instructor for activities like dance and yoga?

I honestly believe that physical movement is the single most effective thing that you can do to improve your happiness and resilience. I’ve always used movement to support my mental health, to deal with stress, find happiness and connection, and build community. For the past 20 years, I’ve seen how movement changes people’s lives and can support happiness, resilience and social connection.

What is happening when we move our body that can have a positive impact on our mental health?

When people are physically active, one of the first things that happens is your brain and body release chemicals like dopamine and adrenaline, which give you more energy, boost motivation, help you focus and make you more optimistic. So any form of movement, any dose, any intensity can make you feel more energized.

If you continue to exercise — say, 20 minutes of at least moderate-intensity movement — your brain is going to really kick into high gear and recognize that you’re doing something difficult and important. It’s going to reward you for your effort by releasing brain chemicals that are very effective at dampening fatigue, physical pain, stress, anxiety, anger, all of the negative interstates that we often struggle with.

At the same time, these brain chemicals enhance pleasure, joy and purpose. So people start to get what we call an exercise high after about 20 minutes. This feeling of whatever was bothering you starts to quiet down, your mind becomes more clear, and then you start to feel like you can take on the world. And this exercise high can last for hours afterward. This profound reset of brain chemistry, it’s one of the reasons on days when people exercise, they’re more likely to make progress on an important goal and have positive interactions with friends and family.

You also talk about recent science that demonstrates this link more directly.

For centuries, human beings thought muscles were only about movement. But in the last decade, biologists have discovered that your muscles are basically like pharmacies, manufacturing, creating and storing different chemicals that are extremely beneficial for your health. Some kill cancer cells. Some reduce inflammation. Some boost immune function. Some help regulate your blood sugar.

Here’s what’s so fascinating: Your muscles store them up and wait until you exercise. It’s only through continuous contraction of your muscles through movement that they start pumping out all of these incredibly beneficial chemicals.

What’s most exciting to me, because I’m a psychologist, is that a lot of those chemicals target your brain. Let’s say you go for a walk or run. You’re using all the muscles of your lower body, your back, your core. They’re releasing these chemicals that will travel to your brain and start to make it more resilient to stress and more sensitive to pleasure, joy and positive motivation.

It’s one reason exercise is so powerful for reducing anxiety and helping people recover, even from things like grief, trauma and addiction. In one of the first papers that discovered this, the scientists called those chemicals “hope molecules.” They help your brain stay motivated, move forward in life, resist depression and despair.

When it comes to the kind of movement you’re talking about, is there a disadvantage for those who face physical challenges?

Most people will think, “OK, but you’re really talking about young people, natural athletes, people without disabilities. You’re not talking about the stroke survivors, people going through cancer treatment, people suffering from severe depression.” And I absolutely am. Hope, joy, connection, meaning, focus, courage — movement is even more likely to give you those things than if you’re young, fit and without any barriers.

It’s all about asking, “What is my body capable of in this moment? How do I connect it to something that has a sense of meaning and purpose, like a positive challenge, or something I enjoy, like nature or music or other people?” Everything that I’m talking about right now, it’s almost more available to you if you do have some challenges around movement or physical health.