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