Your work interval has to be high enough intensity exercise for changes to occur. (flippingfifty.com)
The reason why is because, after training, your muscles become microscopically torn, assuming they've been put through high enough intensities. (gymjunkies.com)
The amount of your total training time spent doing interval training, that is, of high enough intensity to truly increase fat burning, is relatively small in comparison to the base training time. (flippingfifty.com)