Box squats serve different purposes in a training program and can be used for any fitness level.
Beginning squatter? Box squats are great for beginners for multiple reasons. First, squatting to a box forces you to hit the same depth every single rep. This will train your consistency at hitting a parallel squat. Secondly, squatting to a box trains the beginner lifter to begin the motion at the hips and not the knees. Beginning the squat at the knees shifts all the weight forward and this can cause the common mistake of allowing the knees to come too far forward, or the heels to raise up off the floor. Pushing your hips back lets the bar move straight up and down. Thirdly, sitting back onto a box engages the hamstrings more, which tend to be less developed in beginners. Many professionals recommend starting a back squat as a box squat to teach the hamstrings how to fire and explode out of the bottom of a squat.
Want to increase strength? If your main goal is to get stronger in your squats, box squats are your best bet. This is because when you sit down to a box, you are having to stand up with the weight from a dead stop. This is much harder than squatting without a box and being able to rebound out of the bottom using the stretch-shortening cycle in your muscles. For example, if you work up to a 400 pound box squat, then you can definitely free squat the same weight, plus more. Also, when you sit back on to the box, your shins are no longer parallel to the floor (your shins should point towards your body, or “knees behind the heels”). This places all of the stress on your glutes, hamstrings, and lower back. When these muscles get stronger, you don’t have to rely on the quads to stand up and your squat numbers will skyrocket!
Want to improve your squat depth/mobility? It’s very common for a person’s squat depth to become higher and higher as the weight on the bar increases. Box squats automatically indicate when you are lox (low) enough in your squat. If lack of mobility is the reason you have a hard time squatting low, start with a higher box and over time you can begin to squat lower and lower.
Want to squat several times in a week? Box squats don’t make you as sore as free squatting does. Therefore, you recover faster and can perform heavy box squats a couple times a week.