Call the fire department-this squat variation is about to set everything ablaze. Squats will always light up your glutes and quads. But the cardio king of the squat family-the squat jack-does so much ...

(a) Ready for this one? Stand with your feet shoulder-width apart and sink down into a squat – your feet should be flat on the floor, bum out and knees behind your toes. (b) From this position, jump ...