There are two main types of cardio, High Intensity Interval Training (HIIT) and Low Intensity Steady State (LISS). Recall that for the sake of fat loss, cardio is just a tool to get into a calorie deficit and at the end of the day the type of cardio does not really make a difference. The goal of cardio is to simply increase energy expenditure, this means that anything that burns calories can be considered cardio to an extent. This includes anything from biking, walking to the store, running, swimming and so one. Although some forms of cardio (HIIT) can burn calories faster than others (LISS), these forms of high intensity cardio can be a lot harder to sustain for a long period of time and can cause much more of a hit on one’s overall energy levels and levels of exhaustion. To conceptualize it, we will burn calories faster if we sprint than if we were to walk, but we can walk a lot longer than we can do an all out sprint. This means that at the end of the day the amount of calories we burn from both HIIT and LISS can equal the same amount depending on how long we do each for.
LISS on the treadmill for 30 min may burn 250 calories, and at the end of the session we may feel like we barely exercised, on the other hand we may do 10 min of HIIT can also burn 250 calories, but at the end of the session we may feel exhausted.
So how do we do HIIT? As the name suggests, it involves training at high intensities, because the intensities are so high, typically all out sprints, they can only be maintained for short periods of time, usually for around 10 to 30 seconds. After this interval, the individual should do some low intensity exercise for a moderate duration, usually 60 to 90 seconds as recovery. The recovery time should be used to prepare oneself for the next interval of high intensity work. After this active recovery period the next work interval is done at a high intensity. This cycle is repeated for the duration of the cardio session. A typical work to rest ratio for HIIT is 1:3 or 1:4. This means for every one minute of high intensity work, there should be a 3 to 4 minute active rest interval. Any less than this may not provide enough time for a person to recover enough to work at a high intensity. Any more rest and the point of doing the work in intervals is lost.
So what is LISS? Basically it is the opposite of HIIT, where HIIT does work sessions for short times followed by moderate recovery times, LISS involves doing work for long periods of time with little to no recovery. The person will usually do the same level of moderate to low intensity work for the entire session. The heart rate should be slightly elevated, around 120 for most healthy fit individuals aged 20-30, so it is still exercise, but it should be significantly less when compared to HIIT, therefore much easier than doing HIIT.