Each morning, she visualizes what she hopes to accomplish in the water. Sometimes, she'll swim freestyle reps of up to 50 meters as fast as she can without taking a breath. Other times, she'll swim back-to-back 100s and breathe only 15 times. "I visualize my races and even the lead-up to the races," explains Coughlin. "Swimming is so mental."

Mental, yes, but also physically demanding and taxing. After years of tightness in her shoulders and back, Coughlin was diagnosed with double thoracic scoliosis at age 30. From the time she was a teen, she suspected she might have a mild form of the condition, but it was not diagnosed. When doctors x-rayed her spine three years ago and discovered it was shaped like an S, they marveled at how she was able to win Olympic medals with a crooked back. "The theory is that swimming actually hid it, because I've developed muscles so evenly throughout my body to overcompensate," Coughlin says.

And those muscles have been hard-earned. Coughlin trains six days a week, up to six hours a day—morning swims, afternoon swims and weights, plus physical therapy at least once a week. On Sundays, she rests. On Mondays, she starts all over again. If you want to swim as fast as Coughlin, consider the sheer physical strength it takes: She bench-presses 70-pound dumbbells in each hand and does pull-ups with a 45-pound belt strapped to her waist. She can squat 220.

After a disappointing Olympics in London in 2012, in which she won only one bronze medal as part of the 4-by-100 freestyle relay team, Coughlin is back. Last year, she posted career-best times in both the 50-meter freestyle and the 50-meter backstroke, setting an American record in the latter. She continues to train in the pool at her alma mater, the University of California in Berkeley (where she earned a degree in psychology). In 2012, feeling like she needed a change, she parted ways with her coach of 12 years, Teri McKeever, who runs the Cal women's program, and began training under Dave Durden, who coaches Cal's men's team. This means Coughlin now trains with 30-plus men ranging from 18-year-old college freshmen to fellow Olympian Nathan Adrian, 27, who also went to school there. "I'm old enough to be the mother of some of them," Coughlin jokes. "But it's been great—sort of like training with your brothers. The support and camaraderie are huge."

Training with men has also pushed Coughlin's competitiveness. Every Friday afternoon, Durden puts his charges in heats and has them race 15-meter sprints against each other, then calls out the winners. "Out of three-plus years doing this every week, I think I've only won maybe 10 times," says Coughlin. "But when I do win, I'm so happy."

That feeling of victory is something Coughlin dreams of recapturing on the world stage this summer. And if she medals in Rio, it will probably have as much to do with her mental fortitude as her physical prowess. Swimming with the best in the world requires considerable focus and mindfulness. "A lot of people find swimming monotonous, because you're underwater and you're staring at the black line and you're in your own thoughts," says Coughlin. "But, just like in yoga, the practice of being present is such an important thing. It forces you to be introspective. It's difficult, but it makes you mentally strong." I ask if that mindfulness extends to the rest of her life. "Definitely," she says, biting into her pulled-pork sandwich. "Like, when I'm at lunch, I'm at lunch."

A big part of why Coughlin is still able to compete at the highest level is that she has always eaten well, even when her college classmates subsisted on fast food, soda and candy. "I view food as fuel as much as possible," she says of her diet, which is rich in proteins, antioxidants and healthy fats, including olive oil, avocado and nuts. Smoothies are a favorite; she makes them with almond milk and almond butter, plus chia seeds to help with hydration and fiber, and dark cherries to aid with muscle recovery. These are all key when you go from two-hour lifts straight into two-hour swims. "I need a lot of calories to get through my workouts," says Coughlin. Her postrace dinner is usually some sort of lean protein like salmon or black cod with loads of veggies and a grain like farro or brown rice for carbs. "But I don't really limit myself to not having stuff. If I want fried chicken, I'll have fried chicken. Just not every day."