Aerobic fitness, according to Wikipedia, is referred to as "physical exercise (also known as cardio) of relatively low intensity that depends primarily on the aerobic energy-generating process. Aerobic literally means "living in air", and refers to the use of oxygen to adequately meet energy demands during exercise via aerobic metabolism. Generally, light-to-moderate intensity activities that are sufficiently supported by aerobic metabolism can be performed for extended periods of time.
When practiced in this way, examples of cardiovascular/aerobic exercise are medium to long distance running/jogging, swimming, cycling, and walking, according to the first extensive research on aerobic exercise, conducted in the 1960s on over 5,000 U.S. Air Force personnel by Dr. Kenneth Cooper."
Although factual, some would argue that this is an outdated way to exercise anymore and a waste of time. It seems that we are continuously being told that aerobic fitness variation is the key to getting leaner.
The truth be told aerobic fitness variation is just another example or choice of what to do for your aerobic fitness. You might be better served to think of your 'cardio' as
Having made these main points about aerobic fitness variations there are some other terms that also have relevance in the cardiovascular realm and these are low intensity cardio, steady state cardio and interval training.
Low intensity cardio is exactly as the name implies. It is a low grade intensity cardio which is less than 65% of your maximum heart rate. This would include activities like walking and hiking.
Steady state cardio is cardio that requires more of a percentage of your heart rate to be utilized. This is anywhere between 65% - 85% of your maximum heart rate. This includes activities like jogging, eliptical, or biking.
Interval training (or also known as fartleks) is probably the one you've been hearing the most about lately and this of course requires above 85% of your maximum heart rate. This includes activities such as sprinting, or any activity really with high bouts of speed while doing it - so sprints can be applied to running on a treadmill, a rowing machine, a bike etc. But generally, tabata, Spinning and sprinting are the first that some to mind. It is a "feel the burn" activity and cannot be sustained for very long for obvious reasons.
The bottom line is that none of these are useless aerobic fitness variations. When anyone asks me which one is more effective, I have to say, "It depends". It depends on what your goals are, and what activity level you're starting from. Is it fat loss? Improving your aerobic duration for a race? Different goals require different training.
Let me give you an example: If I was training for a show and I was in my last week of workouts before a show, I am not going to be doing any HIIT or interval training of any sort because when I'm going into a show I have decreased my main energy source considerably, thereby reducing my caloric intake and so will not have the energy or the ability to recover like I would with an "off show" diet. So, it depends on your goals to know which aerobic variation is best for you.
What about all of this EPOC business?
EPOC stands for Excess Post-Exercise Oxygen Consumption. In simplified terms, it's your body's effort to return back to equilibrium, or return to it's balanced state. The whole point of doing sprints is the benefit to EPOC. The key is that you have to go all out, meaning you have to go as hard as you can until you can't go anymore (usually a good 12 - 15 seconds for us average folks). It's recovery from this output that you obtain the benefit of the high recovery demand - the work it takes for the body to return to homeostasis.
Is EPOC really necessary for fat loss? You do get hungrier after EPOC because of the increased recovery demand and it's never good to perform in a caloric deficit (decreased calories). No it is not absolutely necessary for fat loss, but it does burn the most TOTAL fat overall in a smaller amount of time. In other words, more total fat is burned during a HITT training session than in doing any steady state cardio and in less time especially compared to time put in.
Steady state can be effective and less intimidating, so I get why people opt for that. If you however are short on time, then EPOC is the way to go.
If you are intimidated by doing short bursts of speed, then you should bring it down to a level that you will benefit from. You can still get your heart rate up with your preferred exercise, recover, and then bring right back up again.