How Does Sprinting/Tabatas Etc. Burn More Fat than Steady State?

[MrMatt]

I don't get this. So let's say I run for 30 minutes at 6.0 mph on a treadmill, twice per week. I burn 475 calories each time roughly. Now if I do tabatas for like 15 minutes, or do a couple 100m sprints and 4 50's I burn maybe...250 each time? See that's what I've never understood, steady state cardio always burns more calories. So where do these other calories that sprinting and things like that burn come from?? So if I go sprinting or do tabatas, and then my pulse returns to baseline a few minutes later, I'm still burning more calories? Is this a post-exercise O2 consumption thing, or a raised metabolism thing? And why wouldn't that raised metabolism break down muscle exactly? I've never understood this, so thanks for any help.

 

[SociallyChallenged]

First of all, talking about burning solely fat during exercise isn't quite right. Perhaps more correctly, we need to just talk about calories as a whole. Both forms of exercise burn calories and, if in a caloric deficit, some of those calories must come from fat stores. If we're talking about calorie use, it really depends on the intensity and repetitions of sprints. Obviously, due to the high intensity of sprints and HIIT, the duration must be much lower than that of steady state cardio. However, because anaerobic energy systems (phosphagens and anaerobic glycolysis) are dependent on oxidative processes to be restored, there is an increased demand for both oxygen and energy utilization post-workout. This excess oxygen consumption and energy creation is utilized to restore/reform ATP, creatine phosphate, and glucose. This is called the excess post-exercise oxygen consumption (EPOC). The EPOC is well studied. It is increased as the intensity and repetitions of sprints increases. However, sprinting rarely burns as many true calories as steady state cardio. It does increase AMPK levels (a marker for oxidative stress and accommodation) higher than steady state cardio, which may help explain why HIIT significantly improves one's endurance even though it seems like an unrelated feat.

Also, to address your question about raised metabolism and muscle: carbohydrates and fat are very easily available as energy stores. Carbohydrates are dominantly used at higher intensities while carbs and fats together are used at lower intensities. Unless your body's glycogen stores are depleted, the amino acids in muscle mass tend to be untouched. If you're working out for periods greater than one hour, you should eat/drink some simple carbs to prevent muscle breakdown (since it gives the body an easier alternative to protein breakdown). No matter if you're doing sprints or steady state cardio, eating a meal high in carbs and protein is essential afterward to prevent post-exercise protein degradation.

 

[edcarman]

Isn't part of the difference also due to the way that you measure calorie consumption?

Heart rate is a poor indicator of intensity for short, high intensity efforts since it lags changes in effort and takes longer than the length of the interval to reach a new steady state. This also means that heart rate-based systems are a poor measure of actual energy expenditure (and hence overall calorie consumption) for HIIT-type workouts, but can be a good indicator for longer, constant intensity efforts.

If I look at the power data from my bike I see that I do about 166kJ of work (directly calculated from power) during a 10min set of 30sec on / 30sec off intervals. During the interval, my peak HR reaches only 86% of maximum and the average is 81% of max. I also know, from other rides, that if I hold the 'on' power for longer periods of 2min or so my HR goes well over 90% of max. For a steady-state ride at around 75% of max HR, I will do around 110kJ of work in 10min. At 81% of max HR it's around 140kJ per 10min. So, although a steady-state session has the same average HR, the actual amount of work done (and hence, ultimately, calories burned) is higher during the interval session.

My figures above indicate that an interval workout burns only around 19% more calories than a steady-state workout at the same average HR and duration. However, the 30/30 session above was not really a true tabata or HIIT workout. I was aiming at a specific power target for the interval and the actual session goal was to complete three sets of 30/30s with steady state riding in between. If I was doing a true tabata workout (4min sets of 20/10 intervals) or a flat out HIIT interval session with only one set of intervals or more sets with fewer repeats, my 'on' power would have been much higher and so would the overall work output. So it is likely that a short HIIT-type workout has a similar work output (and overall calorie consumption) to a steady-state one twice its length.

 

[SociallyChallenged]

Isn't part of the difference also due to the way that you measure calorie consumption?

Heart rate is a poor indicator of intensity for short, high intensity efforts since it lags changes in effort and takes longer than the length of the interval to reach a new steady state. This also means that heart rate-based systems are a poor measure of actual energy expenditure (and hence overall calorie consumption) for HIIT-type workouts, but can be a good indicator for longer, constant intensity efforts.

If I look at the power data from my bike I see that I do about 166kJ of work (directly calculated from power) during a 10min set of 30sec on / 30sec off intervals. During the interval, my peak HR reaches only 86% of maximum and the average is 81% of max. I also know, from other rides, that if I hold the 'on' power for longer periods of 2min or so my HR goes well over 90% of max. For a steady-state ride at around 75% of max HR, I will do around 110kJ of work in 10min. At 81% of max HR it's around 140kJ per 10min. So, although a steady-state session has the same average HR, the actual amount of work done (and hence, ultimately, calories burned) is higher during the interval session.

My figures above indicate that an interval workout burns only around 19% more calories than a steady-state workout at the same average HR and duration. However, the 30/30 session above was not really a true tabata or HIIT workout. I was aiming at a specific power target for the interval and the actual session goal was to complete three sets of 30/30s with steady state riding in between. If I was doing a true tabata workout (4min sets of 20/10 intervals) or a flat out HIIT interval session with only one set of intervals or more sets with fewer repeats, my 'on' power would have been much higher and so would the overall work output. So it is likely that a short HIIT-type workout has a similar work output (and overall calorie consumption) to a steady-state one twice its length.

Measuring caloric expenditure through heart rate for any exercise is inaccurate. People with the same height, age, weight, and gender will burn differing amounts of calories at the same exact heart rate. I'm referring to research where caloric expenditure is measured through indirect calorimetry based on things like the respiratory exchange ratio and duration. HIIT burns more calories per time, but can only be maintained for a short period of time. If you do steady state cardio, it's much more sustainable. I wouldn't go so far as to say you have to work twice as long doing steady state cardio to burn the same amount as an HIIT or sprinting session that is X minutes long. It really depends on intensity and length of rest breaks as well.

 

[gar655]

I don't get this. So let's say I run for 30 minutes at 6.0 mph on a treadmill, twice per week. I burn 475 calories each time roughly. Now if I do tabatas for like 15 minutes, or do a couple 100m sprints and 4 50's I burn maybe...250 each time? See that's what I've never understood, steady state cardio always burns more calories. So where do these other calories that sprinting and things like that burn come from?? So if I go sprinting or do tabatas, and then my pulse returns to baseline a few minutes later, I'm still burning more calories? Is this a post-exercise O2 consumption thing, or a raised metabolism thing? And why wouldn't that raised metabolism break down muscle exactly? I've never understood this, so thanks for any help.

First- Tabatas are NOT done for 15 minutes. It is a strict set of 8 x 20 secs on and 10 secs rest. That's it. No more, no less. If you can do much more than that you're not working hard enough.

Secondly, tabatas are not meant to be done everyday or even every other day, once a week at most.

HIIT/Interval training does not burn more fat/calories than steady state aerobic training, but it does have significant cardio benefits and is an important part of any training if your goal is continual improvement.

Gene

 

[KoolDrew]

In most situations, it doesn't. The people that claim it does are usually under the impression that EPOC accounts for a very large calorie burn, when it really doesn't.

If you're really interested in this topic read Lyle McDonalds very long series on the topic. He takes a very non-bias approach to it, even though it might come off at first that he's anti-HIIT. Hes' not, there's just a lot of BS around about HIIT vs steady state when both have their pros and cons and can/should be used.

http://www.bodyrecomposition.com/fat-loss/stead-state-versus-intervals-finally-a-conclusion.html