Megan Quann wins the gold medal at the 2000 Summer Olympics.

The Olympic aquatic center buzzed with noise. The fans were cheering, but Megan focused on her form—stroke, stroke, breathe, stroke. This 100-meter breaststroke race was her best event.

At the 50-meter mark, Megan was in third place. But she swam a furious final lap, and then it was over. The race was so close that Megan didn’t know the results until she looked up at the scoreboard. It read: 1. Megan Quann, U.S.A. She had won the gold medal! Megan, a teenager from Puyallup, Washington, had traveled to the 2000 Olympic Games to win a gold medal. She had trained hard, and her body met the challenge.

Whether you’re winning Olympic medals, riding your bike, or simply sitting on the couch, your body is at work. Like a complex machine, your body parts work together in systems to keep you breathing and moving.

This text is about the body—the human machine. It’s about Megan’s body, your body, and every human body on the planet. Because on the inside, our bodies all work pretty much the same way.