This problem tends to show up more often with young kids and women, but the error can happen with anyone regardless of age or gender, and - on a rather important note - this problem tends to cause more back discomfort issues than a rounded (i.e., flexed) back.
Don’t get me wrong - we want a straight, rigid back when we squat, so we’re not looking for either an overextended (arched) back or a flexed (rounded) back, but of these two errors, the overextended back tends to cause more problems, and there are two situations which commonly cause this error to happen, so let’s take a look at them.