Picture Lee Constantinou as a young boy growing up in North London: overweight, into video games, last one chosen for pick-up games, suffering from asthma and a lack of confidence. He wasn't, as he readily admits, naturally gifted when it came to sports. That began to change when his dad enrolled him in a local karate school. Four years later, he earned his black belt.

But even then, he didn't really have much muscle on him. "I saw pictures of guys like Jean-Claude van Damme and thought, 'I want to look like that,' says Lee. "I wasn't 16 yet, so I started sneaking into the gym with my older brother to start hitting our upper bodies."

Lee and his brother would do chest and triceps one day, back and biceps another day, and for the last day, shoulders—just shoulders. "We were young then and didn't see any value in working on our legs," he says.

At that time, he was often depressed. He found that by applying the discipline he had learned from martial arts, he was able to progress rapidly with his weight training. The harder he worked, the more his body responded. The more ripped he looked, the more his confidence grew.

Years later, when Lee enrolled at a university, he had his sights set on entering the business world. But he found his heart wasn't in that curriculum. "I switched my major to personal training, got certified, and focused on becoming the most amazing trainer I could be," he says. "I wanted to be good so I could help other people overcome their challenges."

Having surmounted so many barriers of his own, Lee wants to pass on the lessons he's learned the hard way. "I know what it feels like to be out of shape, to lack confidence," he says. "I saw firsthand how developing your body can build self-confidence. I want to pass that lesson on to others."