F45 Training workouts were designed to both unify the muscle groups of the body while helping you move and feel stronger in every aspect of daily life – it moves beyond just appearing shredded and actually helps to streamline movement. The “F” stands for functional training, and encompasses a mix of circuit and HIIT-style workouts. The “45” is the total amount of time each training session takes – but don’t let the quick workout time fool you: F45 gets your heart pumping in a hurry.