Niagara Gazette — With LISS you’re only burning calories at that precise moment, there’s no 16- to 24-hour energy expenditure and boost in metabolism.
This isn’t the most efficient way to do things. Your body will adapt to LISS and you will have to continually increase the duration for the same benefits. With HIIT you are burning calories during the torture session, but also for the next 16-24 hours.
A study conducted at the University of Tampa shows when you add LISS to your workout you get a temporary boost in weight loss. Subjects lost a couple of pounds the first week, than weight loss stalled. This happened because their metabolism completely adjusted to the LISS and that became their new set point to what they had to do just to maintain their current weight.
So, would they do more cardio and eat less to get results? Sounds reasonable but, unfortunately they would likely end up in a worse position. LISS with a low-calorie diet is terrible for fat loss and could cause muscle loss.
If you get too aggressive in your fat-loss goals — too much cardio, restricting calories — you have a strong possibility of losing muscle tissue. At some point, you will likely begin to consume more calories and reduce the amount of cardio you are doing. Once this happens, your body will gain weight. Unfortunately, you’ll gain body fat back and will not gain the muscle tissue that you lost. Essentially, you will weigh more and have a higher body fat percentage which equals a “muffin top” and a slower metabolism.
So why does HIIT work so much better than LISS?
HIIT has been proven muscle retention because when you’re doing LISS — like walking — you’re not activating muscles the same way as if you were lifting weights. When you sprint you have hip flexion, knee extension, and those are movements performed during weight training — like leg workouts. HITT is just another way, like weight training, to overload the muscle.