Dwayne ‘The Rock’ Johnson shares ‘hellish’ bicep routine that gave him 21-inch arms

DWAYNE 'The Rock' Johnson has revealed how to get arms the size of tree trunks - and all you need is a barbell.

The former WWE legend and Hollywood superstar has never been shy in flaunting his ridiculous muscles either on Instagram or the big screen.

And he often provides a few workout tips to give his staggering 137million followers the chance to watch the master in action.

In his latest upload, the 46-year-old showed off a "hellish" routine to bolster those biceps.

He calls it the "21-inch gun salute" and it begins with lifting seven reps from the top going only half way down.

Be sure to pick weights that are reasonably comfortable otherwise it could cause serious injury and you won't turn into The Rock overnight.

Next, without taking a break, he does seven more reps from the bottom going only half way up.

At this point even the Rock appears to be struggling but he powers through with the final stage.

That includes seven full reps before "pushing part your pain threshold to squeeze out a few more extra reps is where success and magic happens."

Here is where you will feel the burn in the arms and even The Rock loses a bit a saliva as he tries to belt out the remaining reps.

In another video where he occupies a LA gym, he writes: "I don't do pretty workouts - I leave that for all the pretty boys. My training is intense, nasty, extreme, apologetic and hard core. But always fun.

"Remember it isn't always about what you do, but rather the spirit in which you do it. Train as hard as you can and leave it all in the gym."

Not only can weightlifting improve your look and mindset, studies through that it can reduce your chances of a heart attack by 70 per cent.

The study – which looked at data from 12,500 people – showed that heart disease fell by 40 to 70 per cent with regular weight training.

It revealed that you don’t need to spent hours in the gym to feel the benefits – a total of 60 minutes a week will do.