In a series of videos posted to Simpson's Instagram story, the two faced off in a challenge to see who could reach the highest Revolutions Per Minute (RPM) on the cardio machine.
Watch the two square off below
In the background, trainer Emily Brabon Hames can be heard saying Karl reached an RPM of 637. Simpson soon follows, but despite his age, is unable to top Stefanovic.
"He's not gonna get there! He's not gonna get there!" Karl can be heard cheering. "Eat my s**t, Simpson."
The SkiErg is one of the most underrated machines in the gym.
“This is a reverse triple-extension move,” Dogpound founding trainer KC McLoughlin previously told Men's Health.
“All the power is coming from your core, your hips, and your legs,” says McLoughlin, who uses the SkiErg in his own workouts to cultivate power and endurance."
“I’ll do 10 100-meter sprints and go as fast as I can, usually towards the end of my workout,” he says.
We'll be following Karl's journey closely from here.