What constitutes proper depth in a squat for it to be valid?

For a squat to be considered valid, the key requirement is that the hip crease must be below the top of the knees. This definition ensures that the lifter is achieving adequate depth during the lift, which is a fundamental aspect of the squat in powerlifting competitions. When the hip crease is below the top of the knees, it indicates that the lifter has successfully performed a full-range squat, demonstrating proper mechanics and control throughout the movement.

While other options describe various aspects of a squat, they do not specifically address the criteria for depth in relation to the knees and hips. For instance, thighs parallel to the ground might suggest a level of depth, but it doesn't confirm that the hip crease is adequately below the knees. Similarly, the requirement regarding the knees not extending beyond the toes relates more to technique and injury prevention rather than defining proper depth. The position of the torso being upright is important for maintaining balance and proper posture during the lift, but it does not directly correlate with achieving the correct depth requirement.