By Deni Kirkova PUBLISHED: 11:26 EST, 12 March 2014 | UPDATED: 13:49 EST, 12 March 2014 Want to get fitter, faster? Then the new Insanity classes rolling out across British gyms could be for you. The hardcore American workout practised by Demi Lovato is focussed on high-intensity interval training (HIIT). She famously tweeted: 'Just did the #Insanity workout DVD... Amazing.. So intense but I loved it!' Insanity is usually practiced at home on DVD, but for British gym bunnies lacking discipline,  a 45-minute gym class has launched where you're put through your paces with the promise of a possible 1,000-calorie burn. To put that into perspective, a spinning class burns just 331 in the same amount of time.
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American top-selling extreme fitness home DVD is loved by Demi Lovato
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Rolls out across British gyms as 45-minute classes
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