James Harrison vs NFL Rookie in Savage Strength Showdown

James Harrison is the KING of crazy strength training videos ... but an NFL rookie might be comin' for the throne.

In the blue corner ... 39-year-old Steelers LB pushing a sled weighing OVER 1,800 POUNDS -- that's one plate for each year of his life.

In the red corner ... 22-year-old Falcons LB Duke Riley pulling an SUV weighing AT LEAST 5,500 POUNDS -- a 2017 Yukon Denali plus his buddy in the driver's seat.

James takes a few tries. Duke did his easy.

Keep in mind, though ... pushing is harder than pulling -- and Duke has wheels workin' for him too.