The Rock begins MMA training as the Hollywood A-lister hits pads and grapples in the gym during 'humbling, intense' workouts... but why has the WWE legend started sparring at 52 years old?

Dwayne 'The Rock' Johnson has shared footage of himself training in mixed martial arts on social media.

In a series of clips posted to his 397 million Instagram followers, the 52-year-old can be seen kicking pads, practicing takedowns and working on his ground-and-pound inside a ring.

The Rock recently enjoyed a successful return to professional wrestling, taking part in a tag-team match alongside Roman Reigns against Cody Rhodes and Seth Rollins at WrestleMania 40.

His age-defying performances inside the WWE ring led to fans calling for a more long-term return to the squared circle.

However, the return was always set to end after the showcase event at Lincoln Financial Field in Philadelphia, to allow him to get started with his current training regime. 

Nearly five years have passed since Johnson announced his production company Seven Bucks Productions would produce a film on former UFC tournament champion Mark Kerr titled The Smashing Machine, with himself playing the lead role.

Work has since begun on the film, with the Rock undergoing an intense physical training regime to help him transform into prime Kerr.

Writing on social media, the 52-year-old described the 'humbling' process of learning MMA, and shared clips of himself practicing takedowns and ground-and-pound.

'Day 1. MMA training camp' he wrote on Instagram.

'Preparing for “Smashing Machine” I’m learning daily and it’s been a very humbling, intense and motivating journey into this world of combat and becoming, Mark Kerr - the two-time Heavyweight Tournament Champion, World Vale Tudo Champion.

'I’m a hard worker, but I realized that I’d have to work harder with this role than anything I’ve ever worked for in my life.

'This physicality is just one part of the larger journey, that is truly a team effort. Growing and grateful.'

One of the first decorated collegiate wrestler to step into MMA, Kerr arrived in the sport during a time where the ruleset we recognise today was still being developed.

Fighting his early contests bare-knuckle with few rules to protect the fighters, Kerr's muscle-bound frame and dominant wrestling skills made him a star of the sport's early days.

Kerr won two one-night tournaments in the UFC, before moving over to Japanese promotion Pride Fighting Championships in 1998.

Chronicled in an infamous documentary also titled The Smashing Machine, personal issues away from the ring combined with poor performances in competition saw Kerr spiral in the early years of the millenium, losing five fights in a row.

Now 55, Kerr retired from MMA in 2009 sporting a record of 15 wins and 11 losses.