Liam Hemsworth has TRANSFORMED for his role in Netflix's The Witcher - insiders reveal the eye-watering Japanese training plan behind his bulk-up

Liam Hemsworth recently posted a photo on Instagram flexing his boulder-like new body. 

The Australian actor, and former partner of pop megastar Miley Cyrus, looked almost unrecognizable from his former slender self - having transformed his body for a new role as heartthrob Geralt of Rivia in Netflix fantasy drama, The Witcher.

But just how has The Hunger Games star managed to achieve such extreme bulk in just over a year?

Insiders have revealed that Mr Hemsworth's impressive new physique is mostly thanks to an intense form of Japanese interval training that was initially designed to get the nation's speed skaters into shape.

Hemsworth posted this selfie showing his progress on his personal account on April 5th, thanking fans for their support of his new movie, 'Land of Bad'.

Hemsworth posted this photo on his Instagram in 2020, sharing his exercise routine with friend and athlete Ross Edgley

The training, called Tabata, has proved crucial to Hemsworth's extreme increase in muscle mass, according to Augustman. 

It was designed in the 1996 by it's namesake, Dr Izumi Tabata from the National Institute of Fitness and Sports at Kagoshima Prefecture, according to Harvard T.H. Chan School of Public Health. 

Dr Tabata and his colleagues developed it as a means of training Olympic speed skaters, according to Total Body Tabata. He found it was a more efficient way to burn calories and raise heart rate than a moderate intensity workout stretched over an hour. 

Modern versions of the workout involve doing as many repetitions of a few different body-weight exercises as possible within a short time period with very brief breaks in between. It's a form of high-intensity interval training (HIIT), which has been sweeping the fitness world for the past decade. 

The goal is to get your heart rate up to a target level over the short period, so that you can burn calories while also building muscle, according to Harvard T.H. Chan School of Public Health. 

This frequent switching between exercises might help you burn more calories than doing a normal, less intense exercise over an hour, according to a 2013 study from the University of Wisconsin. 

'I really enjoy Tabata. High intensity, timed workouts where you do a bunch of different exercises like burpees, bodyweight squats, pull-ups, push-ups, dips,' Hemsworth told Men's Health. 

Hemsworth's specific split includes seeing how many reps of each exercise he can do for twenty minutes, or seeing how quickly you can do 100 of each exercise.

Hemsworth has always had a slim, strong build, such as here, pictured in 2013. However recently he has sported a body-builder type figure with extremely defined pecs and shoulders.

Hemsworth, pictured here in his 2010 film, 'The Last Song', has always been a fan of sports training, and enjoys doing functional exercises

Alongside Tabata, the actor incorporates five 60 to 90 minute strength training sessions per week. This includes deadlifts, squats, pull-ups, push-ups, dips and pull-ups.

He also sometimes rounds out a gym session with a bit of cardio- as if the heart-rate spiking Tabata wasn't enough. In particular, he enjoys cycling, rowing, sprinting and swimming.  

Outside the gym, Hemsworth previously told Men's Health that he enjoys spending time playing basketball and soccer, cycling, surfing and going on hikes. This is key to building functional strength, Luke Zocchi, the Hemsworth brothers' personal trainer, told Men's Health.  

'Liam wanted to be fit, strong and functional,' and enjoys focusing on exercises that improve longevity, like core strength, Mr Zocchi said.