specifics about hiit and aerobic exercise

[navy_seal]

Ok I know that hiit is short bursts then recovery and I know aerobic is a long period of exercise at a set pace. Can someone be specific and tell me the reasons why hiit is better for losing calories eg the science behind it. Also if you do long enough aerobic exercise will it just be as good as hiit?

Thank you

[Phedder]

Neither is inherently better than the other at expending calories. It all comes down to the intensity and duration.

The reason many say HIIT is better for fat loss is due the effect known as EPOC, or Excessive Post-Exercise Oxygen Consumption. Essentially, greater oxygen consumption is required after bouts of high intensity exercise for recovery. This consumption of oxygen relates to energy usage in the recovery process.

Often, LISS (Low intensity steady state) exercise will use more energy during the exercise, but requires much less energy post exercise for recovery. Whereas HIIT may use less energy during the exercise, but it will have put the body in a state where it requires more recovery, and thus more energy post exercise. So HIIT has the potential to expend more calories overall than LISS, but as I already said that depends on the intensity and duration of both. HIIT also takes less time to complete a session that may use an equal amount of calories, if you only have 10-20 minutes to exercise then you'll get a lot more out of HIIT.

Also if you do long enough aerobic exercise will it just be as good as hiit?

That's a fairly loaded question. In terms of just energy expenditure, yes they can be equal. But they're very different methods of exercise, which use different energy pathways and illicit different adaptations. Both can be used very successfully for fat loss alone.

Which one to use really depends on what other goals you have aside from fat loss, and what other concurrent training you're performing. Because HIIT is more taxing on the body and requires more recovery, if you're performing weights 4-5 times a week and HIIT 3+ times a week, while dieting, you're quite likely to eventually run yourself into the ground, and notice your performance in the weights room diminish. Conversely, if you're spending 2+ hours a day distance running, you're likely to lose significant muscle mass as well as fat. Our bodies are fantastic at adapting to what we do, always chasing greater efficiency. If you force it to run 2 hours a day, it's going to change your body to become more suited to doing that, which means losing weight so there's less to carry, which includes your muscle mass.

If you want to get better at running long distances, then run long distances. If you want to get better at operating at a high intensity, then train at high intensities. Makes perfect sense, doesn't it?

Wrote that up quite quickly, so if I've missed anything or if something doesn't quite make sense, don't be afraid to ask for clarification

[navy_seal]

Thank you so much for that write up You said that aerobic requires more energy? How can it require more energy when you are training at a level that has a lower intensity? HIIT totally kills me but aerobic I can do it at a comfortable pace for 40mins

[navy_seal]

Also I heard that if you do hiit you can burn muscle? How come you don't burn muscle when you do aerobic exercise?

[Phedder]

You said that aerobic requires more energy? How can it require more energy when you are training at a level that has a lower intensity?

As I said, it depends on the duration of both. Aerobic sessions usually last much longer, and use more energy during the session. HIIT has a higher rate of energy expenditure, but is usually performed for a shorter duration, so the actual session itself doesn't use as much energy as a long aerobic session. However the energy that is used post exercise for recovery often results in HIIT using more energy over the course of the day, which is what matters most when energy expenditure/fat loss is the goal.

Also I heard that if you do hiit you can burn muscle? How come you don't burn muscle when you do aerobic exercise?

You can. Both can burn muscle, and that will mostly come down to your diet, rest and how you're performing the sessions. If you're not eating enough your body will be forced to burn muscle for energy no matter what you're doing.

I'd actually argue that long aerobic sessions are more likely to burn muscle, and HIIT promotes muscle retention. This is due to two factors; Firstly, HIIT by definition is intense, and thus requires using the muscle near its full potential. If a muscle is being used intensely, the body is going to want to keep it around for future bouts because the muscle is needed to maintain that intensity. Secondly, long aerobic sessions don't actually recruit much muscle at all, it simply isn't needed for the low levels of intensity. Combine the lack of muscle recruitment with long sessions where fuel stores might deplete, and the body turns to burning muscle for fuel. I stated earlier that the body adapts to whatever you're doing, and strives for greater efficiency. High levels of muscle mass are counter productive for endurance based activities, your body wants to cover the greatest distance for the lowest energy cost. It takes a lot less energy to propel a light body than a heavy body, so there's no stimulus from endurance based activities to maintain muscle mass. The bodies response is to drop weight, including muscle, to make it more efficient at covering the distance.

Endurance strives for efficency, HIIT strives for power and maximal performance. A light body is better at running long distances, a muscular body is able to produce the power required for great speeds.

That is taking things to the extremes, but hopefully it helps illustrate my point.