Roller Derby Cross-Training in the palm of your hand, from Roller Derby Athletics! Welcome to your ultimate, sport-specific personal trainer, made by a roller derby athlete, for roller derby. Get stronger and more stable in your skates. Build a rock-solid core. Gain agility and power for jamming and blocking. Feel UNSTOPPABLE! NO TIME? NO PROBLEM Most workouts are 45 minutes or less, and can be done anywhere, without special equipment. Want to lift at the gym? We've got that covered too. The