Comparing HIIT Cardio vs. Low Intensity Cardio for Fat Loss

October 29th, 2007 by Paul Johnson

The average person and many novice bodybuilders, don't know that regular low intensity cardio is not the most effective form of cardio for fat loss. Low intensity cardio burns calories during the activity, but it doesn't increase your metabolism rate afterwards.

HIIT (High intensity interval training) cardio on the other hand, has the ability to raise your metabolism and fat burning capability. This makes HIIT much more valuable then just a simple calorie deficit. You will burn calories from the excercise and for many hours post excercise and more of it will be fat compared to low intensity cardio.

HIIT Cardio Studies:

Post excercise metabolism changes is measured by researchers by EPOC (Exercise Post Oxygen Consumption). When our metabolism increases, our cells in the body require more oxygen.

Two studies done by the same researchers, were published in Int J Obes Relat Metab Disord. 2001 Mar;25(3):332-9. The first study was done on two groups of 352 total men, those who did High intensity activities regularly and those who did not. The study showed that men who were more likely to be in high intensity activities not only had lower bodyfat and subcutaneous fat, but even when they ate more than the sedentary group. The 2nd study was more direct, measuring the effects after a high intensity excercise. They found that oxygen consumption and fat oxidation increased afterwards. They also found that the oxygen consumption effect was much greater in the high intensity group compared to low intensity. In other words, the high intensity group not only had increased metabolism and fat loss abilities for hours post excercise, but the metabolism increasing effect was much higher over the low intensity group. Interesting part is they found these effects to stop with the addition of propranolol, researchers concluded that beta adrenergic stimulation, may be the major role in the after effects from high intensity excercise.

Another study published in Metabolism. 1994 Jul;43(7):814-8 They compared a group (8 women 9 men) doing 20-week endurance-training compared to a group (5 men 5 women) doing HIIT. The decrease in subcutaneous skinfolds when adjusted for energy expedenture were 9 times greater than the endurance group! Researchers concluded that higher intensity, was not only superior for metabolism and fat burning effects, but also for skeletal muscle adaptions.

The study published in (J Appl Physiol (December 14, 2006). doi:10.1152/japplphysiol.01098.2006) done on moderately active women for 2 weeks. Results showed increased capacity in fat burning in muscles and whole body, during HIIT cardio sessions.

Why doesn't every bodybuilder do HIIT cardio then?

HIIT is very intense cardio and is only recommended for very fit people. Even physically fit people should find it very exhausting. Many bodybuilders would just rather walk on a treadmill or bicycle at a steady pace and watch the T.V than do HIIT. HIIT cardio sessions are about 1/3 as long as long as lower intensity cardio sessions. Another consideration is that for hardgainers (naturally fast metabolism), they may find HIIT cardio too catabolic(muscle wasting). HIIT cardio done with leg excercises such as the bike or running, should also be beneficial for helping to maintain leg muscle mass. Doing low intensity cardio instead of HIIT, may cause changes in your muscle fiber type composition, causing your leg muscles to shrink. Weight training during fat loss cycles however, might help ward off these muscle fiber type changes with low intensity cardio.

HIIT cardio should always be done after a meal, since your body will start eating into your muscle, when glucose levels drop during the excercise. Your body needs quick energy to perform HIIT and when glucose runs low, then it moves to protein as an alternative quick fuel source. Since low intensity cardio doesn't have much of a metabolism burning effect, it is recommended to be done in the morning upon wakeup. This is because your glycogen stores will have been depleted and you will be ripe for a state of fat burning during the excercise. Doing low intensity cardio in the day will mostly result in burning carbs. You will create a calorie deficit either way, but it won't be as effective as if you had done it in the morning. In the morning you will be taking advantage of fat burning instead of carb burning. Whether you burn fat or carbs it won't make much of a difference in the long run, since fat loss is mainly about calories in vs. out, but every bit does help.

  1. Sara H. on November 14th, 2007

    Exciting review discussing ring HIIT Cardio vs. Low Intensity Cardio for Fat Loss. Thoroughly love your posts.

  2. Fola on March 4th, 2009

    I love this! Thanks so much for the information and clarification. It helps seeing that it is ok to eat before the HIIT cardio session, as there are so many differing opinions. I love high intensity workouts, so much more exciting and gives you something to long for when you are about to build up to that next high interval and you’ve got your music climaxing to!

    🙂 Thanks,

  3. bob on December 8th, 2009

    Nice article but it seems a bit biased.

  4. jp mallari, otrp on February 28th, 2011

    very very useful unbiaseed information!