Actor Ryan Reynolds is ready to do the unthinkable for a cause he believes in: exhaust himself physically and mentally and show his vulnerability during the frightening, for him, New York City Marathon on November 2.

Ryan Reynolds has written an emotional open letter on The Huffington Post where he bravely looks at life’s mysterious ways and how, from cowering in terror at the thought of bloody nipples he is now ready to take the risk of suffering the horrific injury himself.

All in the name of standing up for a noble cause.

Reynolds recounts how two years ago he witnessed the last part of a New York City Marathon and how impressed he was with the participants’ incredible willpower and effort. How amazed he was to see them suffer for their victory, how they reached the finishing line “crying, limping, hobbling, screaming, crawling” yet experiencing “sublime rapture.”

The detail that most astounded him were guys finishing the race with bleeding nipples – “Why in the hell were their nipples bleeding?” and he promised himself that day that he would never, ever subject himself to such a terror. “Bleeding nipples. Bleeding. Nipples.”

Maintaining the humorous approach, Reynolds goes on to explain how this Nov. 2, he too will attempt to reach that finishing line, on behalf of his father, Jim Reynolds, who has spent the last 15 years struggling with Parkinson's Disease.

The actor found inspiration in Michael J. Fox, whom he says he admires wholeheartedly for his own struggle with the disease and for his ample endeavors to help others afflicted.

Reynolds invites all those interested to donate to his cause or another and to come witness his own pain next month as he becomes the first participant to “sob uncontrollably” for 26.2 miles straight.

Ryan Reynolds may just have one very special supporter during the marathon: his wife of less than two weeks, Hollywood star Scarlett Johansson.