Answer:
Bright as diamonds, loud as thunder, never still, a thing of wonder. What am I?
I make you weak at the worst of all times. I keep you safe I keep you fine. I make your hands sweat and your heart grow cold. I visit the weak but seldom the bold.
I can be winding and I can be straight. I can be smooth and I can be rough. Sometimes both. I start out black but fade to brown. My favorite colors are yellow and white and I love stripes and dashed lines.
What gets sharper the more you use it?
I am an English word with 3 consecutive double letters.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.