I am the end of the able yet the beginning of the rest.
I am without feeling yet I can cause a heart to break.
I am synonymous with pain yet endorphins provide relief.
I am not indefatigability yet I am a related antonym.
I am renowned for incapacitating yet am really quite nice.
I am a scourge to some yet I am sought after by others.
I am more acute in some bodies yet no body is above me.
I am a free spirit yet can be controlled by a strong mind.
I am a regular at marathons yet I usually wait until the end.
I am started with exertion yet I always finish with an ion.
I am audible like a tailpipe yet I emit identical dioxides.
WHAT AM I?
Last edition’s Fustigator: Miracle