Looking up at the ceiling when squatting has so many detrimental effects on proper technique that some law against it will eventually have to be adopted. It is the enemy of correct bottom position, hip drive out of the bottom, and correct chest position, the three most important factors in a safe, correct squat. This bizarre neck position is inherently unsafe anyway. To place the cervical spine in extreme hyperextension and then to place a heavy weight on the trapezius muscles directly underneath it is, at best, imprudent.
Try this: assume a good deep bottom position as described earlier, with knees out, toes out, and heels down. Put the chin slightly down and look at a point on the floor five or six feet in front of you. Now drive your hips
up out of the bottom, and make note of how this feels. Now do the same thing while attempting to look at the ceiling (fig. 2-25). You will discover an amazing thing — that chin-down (looking down keeps the chin down) with the neck in a normal anatomical position enables your hip drive. And it helps you keep your chest up, so that your upper back is in the normal anatomical position for the thoracic spine under load. Correct chest position is an important factor in placing the lumbar spine in the correctly extended, slightly arched position. Correct lumbar position is essential for full utilization of the hamstrings and glutes out of the bottom, because when they are stretched more completely they can contract more completely and generate more power over a longer range. So bad neck position sets up a series of bad positions that greatly diminishes the safety and effectiveness of the squat.