If you run, you will need me,
If you live, you will breathe me.
When you climb a mountain,
I will start to disappear,
No matter how hard you listen,
No sound will enter your ear.
I'm a reason you're alive,
Without me you would surely die.
The way I come in is not the way I get out,
Another hint is that you use me more when you shout.
Without a helper I would not get in or out at all.
What am I, and what is my helper?
I am oxygen, and without the diaphragm (the helper) I would not get inside the lungs.
Today's brain teaser courtesy of Braingle.com.