Tim Duncan hitting the gym hard this offseason

Tim Duncan is one of the oldest active players in the NBA, but he’s coming off his best season in nearly a decade.

What’s his secret to staying in shape?

The Spurs power forward has been spending this offseason training, not on the basketball court, but in the boxing ring.

And Duncan isn’t taking on amateurs. He has been working with two-time world boxing champion Jesse James Leija.

Duncan knows a little bit about winning championships himself, but he came up seconds short of his fifth ring against the Miami Heat in last season’s NBA Finals.

Leija is retired, but he’s helping Duncan get one more title before wrapping up his Hall of Fame career.