Having three sons himself, fitness guru Curtis Hoekstra understands how finding time to exercise can sometimes be difficult when juggling busy work and family schedules. That’s one of the reasons why he designed Rock Star Boot Camp’s workouts to be fast—each only 40 minutes along. But his interval-based “9xFit” training system isn’t for slouches, packing a mix of strength training, plyometrics, core conditioning, and other types of exercise into one dynamic session. Over the course of the workout, boot camp attendees will warm up with some calisthenics before launching into exercises tailored to their individual needs. Cardio training also factors in, eschewing treadmills and other machines in favor of metabolism-boosting bodyweight circuits. The co-ed fitness classes are held in an indoor/outdoor warehouse.