May 13, 2016, 12:16 p.m. (ET)

Marlen Esparza has never understood the barrier between women and boxing, but she hasn't let that stop her. Without having a female boxer to mentor her, Esparza was forced to train with the boys. They never went easy on her, which Esparza says was a blessing, because it helped turn her into the world-class boxer and Olympic bronze medalist she is today.