Former Titans star Chris Johnson reveals ALS diagnosis

Former Titans star Chris Johnson revealed in an emotional interview with "Good Morning America" today that he was diagnosed with ALS.

The big picture: Johnson, 40, told interviewer Michael Strahan, who is also a former NFL standout, he intends to fight the devastating disease with no known cure.

"Honestly, I don't know if you ever fully process it," Johnson said, speaking with the help of a computerized device. "At first you're in shock, then you realize you have two choices. You can give up, or you can fight. I chose to fight."

Flashback: In a sport of super-athletes, Johnson was even more explosive than almost all NFL players. He recorded one of the fastest-ever 40-yard dash times at the scouting combine.

After the Titans selected him in the first round of the 2008 draft, Johnson rushed for 9,651 yards and 55 touchdowns in his career.

He was known for his blazing speed and ripping off explosive long runs.

"Some people leave a mark on an organization that you just can't put into words," Titans owner Amy Adams Strunk said in a statement. "Chris Johnson is one of those people for us. Learning this news is extremely difficult, and we will support Chris every step of the way throughout his journey."

Zoom out: The shocking diagnosis is already familiar to the Titans family.

Johnson's former Titans teammate Tim Shaw was also diagnosed with ALS, and has been living with the disease since 2014.

Zoom in: Nashville has become a hub of ALS advocacy and research, culminating in the state giving a record-setting grant to Vanderbilt's research center earlier this year.

Watch Johnson and his wife Brittany Johnson's full interview