In an effort to teach athletes the thigh level position when doing the squat many coaches use box squats. The concept of this exercise is good but execution of the exercise is potentially dangerous. Perhaps even more important is the question of whether box squats are even needed.
If athletes do enough correct repetitions of the squat, I see no reason why they would not develop the kinesthetic feel needed to recognize the thigh level position. If this is so, why are box squats needed?
Understand that all athletes develop a kinesthetic feel for an exercise if a sufficient number of repetitions are done in the same manner. The most important factor is that each repetition is done with the same technique. This is the key to developing a strong kinesthetic feel.
The opinion regarding the thigh level position as being a critical factor in an effective squat is also open to criticism. Why is this position so important? Is the squat not effective if the body is lowered to a point where the thigh is at a 45-60° angle to the vertical?
In many cases this angle may be more effective for athletes who are involved in jumping and running. The reason for this is because it more closely duplicates the knee angle seen in execution of these skills. In addition, this is a safer knee position for very tall athletes.
Another factor that is often overlooked when trying to achieve the thigh level position in squatting is whether the spinal column is held in its normal, slightly arched, lumbar position. This is important in not only for better support of the weight on the shoulders but for safety of the spinal column.
Because of this I always strongly recommend that spinal position should be the key factor for determining the depth of the squat. Many athletes, in trying to achieve the thigh level position, round the lower spine which creates a very dangerous position. The danger increases as the weight being supported is increased.
If you closely watch a person do a box squat you will see that they too round the lower back to get their weight forward in order to stand up after sitting on the box. I have never seen anyone do box squats while maintaining the normal curvature of the spine throughout the entire moment. The greater the weight that they use, the greater the chance of spinal injury occurring.
In light of all of these factors should you do box squats?
For more information on the squat see Biomechanics and Kinesiology of Exercise.