Originally Posted by Danny
My personal suspicion about all this discussion that spearing deeper helps keep your legs up amounts to the simple observation that, if you spear too high, your spine arcs and it ruins your alignment. So it's not really the weight of the arm up front, or anything like that. Spear wherever you want as long as you can keep a straight spine, and you'll be OK. As soon as your spine starts to bend, your legs will also drop.
Arching the back will induce a downward force at the hips/legs. Since water is not solid, you are only bracing against your buoyancy point, which is at your lungs, where the air keeps you afloat. That is why your hips drop when you arch your back.
Try it yourself. Launch into SG. Maintain good posture and see where your hips are at. Then arch your back. What happens? You don't even have to raise your lead arms. Then try it in Skate. Arch the back without raising the lead arm. What happens?