I tried this lower-body workout from ACE-certified personal trainer and Blogilates creator Cassey Ho, and in four minutes it lit up my quads big time. Of course, it's set to "All I Want For Christmas Is You" and features narrow squats and narrow squat pulses, side squats, sumo squats and sumo squat pulses, as well as fun dance moves. When I do this next, I'm going to add weights and repeat it a second time to make it even more challenging.