What do it mean to be "Planting Under"?

[fpt2012]

I was looking up how to relieve lower left back pain, and they said, that it is cause by "planting under"
I don't know what it means so I can't fix it.
Can you please help me I want this pain to go away.
Thank you

[VaultPurple]

When your takeoff foot is on the ground and your top hand is as high in the air as possible with the pole tip in the back of the box, you should make a right triangle with you, the pole, and the ground. For instance if your body makes a right angle with the ground at 11' but you are taking off at 10', you are a foot under.

[vcpvcoach]

What vault purple said or, simply, from your last step, you should draw a line from your foot straight up to your top hand. If you toe on your takeoff foot is right under your top hand, you are right on. If you toe is towards the box , you are under.

To fix it, run upright with high knees. Make sure your plant is on time. If it's late, you will always be under.

[vquestpvc]

A thing to remember is that pole vaulting, despite many efforts to the contrary, is another track and field jumping event. Be that as it may, I believe many vaulters are "under" because they don't "jump" at takeoff; especially young vaulters. Meaning, the takeoff foot needs to be put down through the ground creating a jumping action instead of "running" through the takeoff. Running through the takeoff, instead of jumping at takeoff, causes one to stride past the optimum point where the top hand is over or slightly in front of the takeoff foot. Funny how the same "under" concern is "over" in the long jump when both events have many similarities; similar driving approach, similar upright position at takeoff, but more importantly an athlete needs to jump at takeoff. If a long jumper "runs" through a jump they may be "over". If a jumper is on the board while "running" off the takeoff the jump will be "flat" with little distance. For a high jumper, "running" through may mean blowing through the cross bar. "Jumping" makes it possible to clear a bar in the high jump. So, any individual just learning to vault must learn to jump. Spend time in particular learning to long jump as well as vaulting. And please, before someone suggests that you move back because you're "under", ask yourself: am I actually jumping at takeoff? Honestly, pole vaulting is not that difficult or as difficult as some would have people believe. But, one should learn the basic mechanics for safety and success!