Justin Timberlake and Jessica Biel are literally freezing their butts off.

The 'Rock Your Body' singer and his actress wife are fans of cryotherapy,

a new weight-loss technique which involves standing in a tank at subzero temperatures for three minutes in order to burn calories.

Standing in the icy tanks prompts the body to go into overdrive to keep warm burning up to 800 calories at a time.

Cryotherapy is also thought to fight inflammation and an insider revealed Justin is also using the treatment

to help with muscle pain during his intense rehearsals for his upcoming tour.

Good luck Justin!