Artur Beterbiev is one of the most destructive punchers in boxing today.

The heavy-handed Russian is the only active world champion with a 100 per cent knockout rate, having finished all 20 of his fights inside the distance.

Beterbiev is showing no sign of slowing down at 39GETTY

On Saturday night, he aims to make it 21 when he squares off against Dmitry Bivol for all four major sanctioning body belts at light heavyweight.

And three days before the much-anticipated showdown, Beterbiev and Bivol took to the ring in Riyadh, Saudi Arabia for their open workouts.

While Bivol opted to hit the pads, Beterbiev started off his routine by performing an insane wrist workout that left onlookers stunned.

The remarkable exercise, which has been coined the ‘Iron Fist’ by fans, involves Beterbiev exploding from a press-up position down into a flat fist, a clenched fist and then onto the back side of his hand.

He then transitioned into a hand stand on his forearms.

Beterbiev’s trademark drill helps build wrist and forearm strength, which are crucial components of punching power.

Reacting to his gruelling workout, one fan wrote: “He’s a machine, we’re in for a good one this Saturday.”

Another added: “This guy is a beast!”

A third tweeted: “Always thought Bivol would beat him but now I can’t decide.”

A fourth asked: “Why would you ever want to fight a man who trains like this?”

Beterbiev performed a hand stand on his forearms to finish his insane routineGETTY

Meanwhile, another fan posted: “And people were saying he’s old earlier in the week…”

DAZN presenter Ade Oladipo was just as impressed by Beterbiev’s feat of strength.

“Honestly, one of the craziest workouts I’ve ever seen,” he said on the broadcast.

“Some of the stuff he was doing in there. They say he is 39, I think someone needs to check his passport.

“He looks like a man that could be 30. Incredible from Artur Beterbiev.”