Many cite winning more Super Bowls, defying father time and general love of the game as the main reasons for Tom Brady still football playing in his 40s.

But the New England Patriots quarterback is focused on something far more specific, apparently.

In an Instagram post Friday afternoon, Brady shared a video of himself sprinting on a beach with a resistance band around his waist. In the caption, the 40-year-old future Hall of Famer, who has 968 career rushing yards, revealed the real reason for why he hasn’t retired: the pursuit of 1,000 yards on the ground.

(You can click here to view Brady’s video.)

“Ok so the main reason I’m still playing is I haven’t hit 1,000 career rushing yards yet,” Brady wrote. “… 32 to go! #TB1K #CatchMeIfYouCan #whereyouatAP #watchandlearnruss #cominforyouarodg #notsoeasyanymorevon #qbsneakon3rdand1”

Brady’s post garnered appropriate reactions from some of his past and current teammates.

“I actually laughed,” Jacoby Brissett wrote, along with some laughing emojis. “I’m ready for our race,” Brady replied.

“I’ll still beat u in the conditioning run!” ex-Patriots long snapper Lonie Paxton wrote, to which Brady replied, “no chance doc.”

“It’s only taken u almost 21 yrs to do it studdd,” Willie McGinest quipped.

NBA guard Isaiah Thomas also shared his two cents, saying “Looking quick TB lol.”

There were many more reactions, including one from Mark Wahlberg, but you get the idea.

Brady recently ended offseason speculation by confirming he’ll play for the Patriots in 2018. As for his pursuit of 1,000 rushing yards, it might seem like a tall order for the slow-footed QB to rack up 32 in a season — but would you doubt him?

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Thumbnail photo via Mark J. Rebilas/USA TODAY Sports Images