Why chest up can be a terrible cue for some athlets during squatting.
Occasionally I run into an athlete (usually a very flexible female or someone tight through the quads and hip flexors) who can’t seem to keep a neutral spine through out the range of motion of their squat. As they are standing everything looks beautiful and strong, but as soon as they start, their first move is to create an anterior pelvic tilt. Similarly you might find that an athlete gets to the bottom of their squat appropriately but as soon as they engage to move back up, the first thing you see is that anterior pelvic tilt and extension trough their spine. This extended position through their spine with is why “chest up” can be a terrible cue during a squat. Of course when using this cue we are simply trying to discourage too much hinging at the hip and putting tons of shear force across their spine. This is why you need to know how your athlete moves, and pick appropriate cues to illicit the response you are looking for. If you find you yourself are prone to being over extended trough your spine while squatting, it is important to take a step back and fully learn what it means to be braced and neutral.