As a fitness trainer known for calisthenics, I'm often asked about adding weights to squats. Though bodyweight training has become more acceptable as a legitimate tool to sculpt the upper body, some people are not convinced that it can do the same for the lower half.

There are actually several variations within the bodyweight-squat family that will strengthen and sculpt your legs and butt using zero equipment. With progressive bodyweight training, you never have to add any external load to your squats in order to get stronger.

Two of my favorite ways to progress bodyweight squats are to move them into other planes of motion—lateral or rotational, for instance—or to remove a point of contact. Single-leg squat variations not only build strength, they test your unilateral stability and balance, too. When you're learning them, don't be surprised if you "feel" them in places beyond your quads—like your hips, glutes, and even your core.

Here are three awesome squat variations that can shake up your stale squat routine!

Skater or "Curtsy" Lunge

The curtsy lunge, sometimes called a skater lunge, is a unilateral squat variation that will target the outer legs, hips, glutes, inner thighs, and ankle joints. It can be practiced dynamically at a slow pace or explosively by jumping from side to side giving it that "skater vibe."

In a standard lunge, you step one leg directly behind your hips, keeping the same parallel position. In a curtsy lunge, however, you increase the range of motion by stepping your leg not only behind, but also across your other leg. This exercise is unique, because unlike most of what happens in the gym, it puts you in all three planes of movement: sagittal (front to back), frontal (side to side), and transverse (rotational).

Curtsy Lunge

Begin by standing with your feet hip-width apart and your arms at your sides. Initiate the lunge by taking a big step behind and outside your front leg, balancing on the ball of your back foot. Bend your back knee, allowing it to hover a few inches above the ground. At the bottom position, the shin of your front leg should be more or less vertical. It can be helpful to bring your arms up into a fighter stance or place your hands on your hips to improve your balance as you lunge.

Maintain a neutral pelvis by rolling your tailbone under to engage your abs at the bottom position. Return to center by fully extending your hips and legs, and repeat on the opposite side.

Archer Squat

This squat variant involves squatting to one side as you extend your opposite leg. You may see it called a "Cossack squat" by some people. This squat increases flexibility in your legs by stretching your inner thighs, groin, hamstrings, calves, and even the muscles of your ankles. Like the skater lunge, the archer squat also strengthens the muscles of the outer hips, quads and glutes.

If you are particularly tight in the places this move hits—and most of us are—it can help to practice this move by holding on to a suspension trainer, bar, or other sturdy object for support. When you hold on to an object, it minimizes the challenge of stabilizing your spine as you squat, helping you stay more upright and allowing you to go deeper into the bottom position.

Archer Squat

Begin with your legs significantly wider than your hips and your toes turned slightly out. You'll probably have to experiment to find your ideal width. Reach your arms forward as you bend one knee and squat to that side. As you lower yourself, slowly begin to turn the toes of your opposite leg upward so you are rotating on to your heel and flexing your foot. You may need to lean fairly far forward at first in order to engage your abs if you are particularly tight in your ankles or hips, but don't let that heel come up!

At the bottom position, your knee should be tracking in line with the toes of your squatting leg. Squeeze your glutes, push through your heel, and turn the toes of your opposite leg forward as you flatten your foot to return to a standing position. Transition to the other side and repeat.

Hover Lunge

The hover lunge or "airborne" lunge is a unique variation where you keep your back leg hovering above the ground as you lunge, rather than touching the toe to the ground as you would in a standard lunge.

This might not sound like a huge change, but it requires plenty of stability in the foot and ankle joints of your standing leg, as well as powerful hips, serious core strength, and laser-like focus. Fortunately, it can help you build these attributes, too! When you are learning this variation, it may help to practice on a mat or other soft surface behind your standing leg in order to avoid crashing down on your back knee while you learn to control the descent.

Hover Lunge

Begin standing on one leg with your opposite knee bent and that foot out behind your body. Extend your arms forward as you bend into your standing leg, reaching your opposite leg behind you. Lower until the knee of your hovering leg is a few centimeters away from the ground before standing back up.

It may feel like a long way down at first, so take your time. You will need to lean your chest forward more than you do in a traditional lunge to maintain your center of gravity over your lead leg. Like the archer squat, it can help to hold on to something for balance when you are learning this difficult variation.