For buns that defy gravity, the lunge is the move to do. Lunges target the glutes and quads, and there are a variety of ways you can perform them.

To do a basic forward lunge, start in a standing position. Take a big step forward with one leg, so that your knee is right above your ankle. "Make sure your front heel is always down while you lunge. The focus should be on your front leg/glute/heel and never the leg that's behind," Mathews says. "I often tell people that it is similar to the lunge of 'tying your shoelaces.'" Lower your body down so that the opposite knee lightly kisses the ground. Step back into your starting position, and then repeat on the opposite leg.

You can also perform a jumping lunge; instead of stepping back into the starting position, jump up switch your legs in midair (you should land with the opposite foot forward in the lunge position).

Squats are a foundational movement in Crossfit. And, if you want a butt that looks like it could squat for days, you've got to, well, squat for days. Squats are a great lower body workout, because they work the muscles in your glutes, hamstrings, quads and inner thighs.

An air squat is a fundamental bodyweight movement that sounds easy, but can be difficult to perform with full range of motion. "Your feet should be slightly wider than your hips and pointing more forwards than outwards," Mathews says. "This will allow you to drive your hips outward as you squat to create tension in the hips and use the glute muscles more." An ideal squat is "ass to grass:" your hip crease should fall below your knees. If you can't get that low, focus on form over depth. Meaning: keep your chest up the whole time, and never let your knees go past your toes.