Kettlebells are unmatched in their ability to give you an amazing cardio and strength workout at the same time. The basic kettlebell swing (the simplest kettlebell move of all) involves swinging the bell from the ground out in front of you to shoulder height and back down again. It sounds easy, but most people don't use proper form and risk serious injury to their back. To master this move, "reach back with your hips on the backswing as if you are trying to touch a wall behind you," says Jenn Nims
, RKC certified kettlebell trainer. "As you do this, keep your shoulders back and your spine neutral. At the top of the swing, contract your abs as if you're getting punched in the stomach, while simultaneously squeezing your glutes as if you're crushing a penny. Maybe not the best image, but it helps people to activate the right muscles."
Tip: You should feel this move in your inner thighs, quads, and especially your glutes. If you feel a pull in your lower back, you're doing it wrong.