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.

Justin, 37, and Jessica, 36, are regular visitors to Quick Cryo in the Tribeca district of New York, according to the New York Post's Page Six Column.

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.

The insider said: ''When Justin is in town, he and Jessica are here every other day.''

The 'SexyBack' singer has also been using the spa's oxygen bar before getting frozen, which is said to boost the effects of the therapy. Cryotherapy costs $85 per session, or $600 a month for unlimited membership.

Justin and Jessica - who married in 2012 and have two-year-old son Silas together - recently put their New York penthouse on the market.

The lavish apartment - which comes with three bedrooms and three-and-a-half bathrooms - is listed at $7,995,000, and according to the description, the lavish pad comes complete with 10-foot tall ceilings, a gas fireplace, custom wood paneling and floor-to-ceiling windows.

The property is part of an apartment building which also comes with communal art gym and fitness centre, as well as a common garden.

The couple's decision to sell their New York penthouse comes as they spend most of their time in California, and sources recently revealed they are looking to add another member to their family.

An insider said: ''It's 'when' not 'if' they'll be adding to their family. They've always wanted another kid, but they waited until things got better. Now they are trying, hoping for a girl.''