Answer:
What you become during a workout?
What must be looked through in order to see?
It's in your hand though you cannot feel it. Only you and time can reveal it.
What has thousands of ribs and two backbones?
It covers you, you lose it every day and you'd die without it.
I break away from my pack. I create holes in my victims. I can travel for miles and then disappear. I am part of a dying breed. What am I?