This may help with optimising HIIT for fat loss

T

Tezza

New Member
I just came across something at misc.fitness.weights and thought it may help our HIIT quite a bit for losing fat. I'll post the whole post plus the url. Enjoy.
I am interested in your thoughts on the following section of an
article by Christian Finn. The abstract he bases his comments on is
at the end. Thanks.--James.
Short or long intervals?
Research published in the European Journal of Applied Physiology
compared the fat-burning effects of two different interval training
workouts, both lasting 40 minutes [2].
The first consisted of short intervals lasting 6 seconds, with
9-second rest periods. The second workout involved long intervals
lasting 24 seconds, with 36-second rest periods.
It's important to note that the treadmill speed was identical during
both the short and long interval workouts.
Moreover, the ratio between work and recovery bouts was also the same,
meaning that the total amount of time spent running on the treadmill
(16 minutes) was also identical.
Despite the fact that exercise intensity and duration were kept
constant during both trials, there were large differences in fat
oxidation.
In fact, the number of fat calories burned was approximately 3 times
LOWER during the long (24 seconds) interval workout.
To understand why the short intervals were so much more effective at
increasing fat oxidation, it's important to understand a little more
about a substance called myoglobin (pronounced my-o-globe-in).
What is myoglobin?
Myoglobin is a large protein that binds to oxygen inside your muscle
cells [3]. Think of it a little like a "reserve" oxygen supply.
Per Olof Astrand, whose Textbook of Work Physiology is required
reading for many exercise science students, first proposed a role for
myoglobin as an oxygen store during interval exercise way back in the
1960's [1].
According to Astrand, myoglobin is repeatedly used and reloaded during
the work and recovery phases of interval exercise.
However, as the duration of the work period's increase, myoglobin
stores are reduced.
Your body needs more oxygen to use fat as a fuel (compared to
carbohydrate or protein). When oxygen supplies become limited,
carbohydrate supplies a greater proportion of energy.
Because lactic acid, a by-product of carbohydrate metabolism, "blocks"
fat burning, intervals that continue beyond the point at which
myoglobin loses its supply of oxygen rely to a greater extent on
carbohydrate as a source of energy.
How long do myoglobin stores last?
Myoglobin holds enough oxygen to last for 5-15 seconds [1].
This explains why short, rather than long intervals appear to promote
a greater rise in fat oxidation.
As such, if your goal is to lose fat, then limit your work intervals
to a maximum of 15 seconds.
Studies also show that shorter intervals don't feel as physically
demanding as long intervals -- so you can get better results without
feeling like you're working harder.
How long should my rest intervals last?
This depends on the duration of the work intervals.
The longer the work interval, the more myoglobin gets used up, and the
longer it takes to "reload".
The study we looked at earlier used rest intervals that were 1.5 times
greater than the work intervals (6 seconds work: 9 seconds rest).
Based on these findings, a 15-second work interval would require a
minimum of 22 seconds rest.
If you've never tried interval training, a rest period lasting 45
seconds might be a good place to start.
As your fitness level gradually improves, you'll be able to gradually
reduce your rest time.
Medline Abstract
MA Christmass, B Dawson, and PG Arthur
Effect of work and recovery duration on skeletal muscle oxygenation
and fuel use during sustained intermittent exercise.
Eur J Appl Physiol Occup Physiol, October 1, 1999; 80(5): 436-47.
[Abstract]
--------------------------------------------------------------------------------
Department of Biochemistry, The University of Western Australia,
Nedlands, 6907, Australia. [email protected]
The purpose of this study was to compare rates of substrate oxidation
in two protocols of intermittent exercise, with identical treadmill
speed and total work duration, to reduce the effect of differences in
factors such as muscle fibre type activation, hormonal responses,
muscle glucose uptake and non-esterified fatty acid (NEFA)
availability on the comparison of substrate utilisation. Subjects (n =
7) completed 40 min of intermittent intense running requiring a
work:recovery ratio of either 6 s:9 s (short-interval exercise, SE) or
24 s:36 s (long-interval exercise, LE), on separate days. Another
experiment compared O(2) availability in the vastus lateralis muscle
across SE (10 min) and LE (10 min) exercise using near-infrared
spectroscopy (RunMan, NIM. Philadelphia, USA). Overall (i.e. work and
recovery) O(2) consumption (VO(2)) and energy expenditure were lower
during LE (P < 0.01, P < 0.05, respectively). Overall exercise
intensity, represented as a proportion of peak aerobic power
(VO2(peak)), was [mean (SEM)] 64.9 (2.7)% VO2(peak) (LE) and 71.4
(2.4)% VO2(peak) (SE). Fat oxidation was three times lower (P < 0.01)
and carbohydrate oxidation 1.3 times higher (P < 0. 01) during LE,
despite the lower overall exercise intensity. Plasma lactate was
constant and was higher throughout exercise in LE [mean (SEM) 5.33
(0.53) mM, LE; 3.28 (0.31) mM, SE; P < 0.001)]. Plasma pyruvate was
higher and glycerol was lower in LE [215 (17) microM, 151 (13) microM,
P < 0.05, pyruvate; 197 (19) microM, 246 (19) microM, P < 0.05,
glycerol]. There was no difference between protocols for plasma NEFA
concentration (n = 4) or plasma noradrenaline and adrenaline. Muscle
oxygenation declined in both protocols (P < 0.001), but the nadir
during LE was lower [52.04 (0. 60)%] compared to SE [61.85 (0.51)%; P
< 0.001]. The decline in muscle oxygenation during work was correlated
with mean lactate concentration (r = 0.68; P < 0.05; n = 12). Lower
levels of fat oxidation occurred concurrent with accelerated
carbohydrate metabolism, increases in lactate and pyruvate and reduced
muscle O(2) availability. These changes were associated with
proportionately longer work and recovery periods, despite identical
treadmill speed and total work duration. The proposal that a metabolic
regulatory factor within the muscle fibre retards fat oxidation under
these conditions is supported by the current findings.
It was found at http://groups.google.com/groups?....weights
 
I'm not so sure. HIIT is an anaerobic activity - its very intensity is why carbs are burned preferentially to fat. More fat calories are burned in regular 30-40 minute low-intensity cardio, and a higher percentage of calories are burned in fat any given minute of low-intensity cardio than HIIT. Yet, HIIT has been shown to boost overall metabolic rate and create positive conditioning effect superior to that of low-intensity cardio, due to this metabolic fatigue. So in reducing the intensity (by using shorter cycles), would you be hurting the advantages of doing HIIT?

However, I've found shorter intervals is actually harder than longer. It's unlikely that your peak speed at 6 seconds is less than for 24 seconds. The abstract suggests they had the trainees run at identical speeds for both interval protocols. I don't believe real-world HIIT works like that . . . or maybe I've been doing this wrong all along! :D

cheers,
Jules
 
I have the same point of contention that jules poses. however, there are certain conditions in which the postulate about the fat burning effect may hold true. i am also not so quick as to disregard what you mention as i know i have been a victim of the 'dumbing down' of the final message in many texts. In other words it is not uncommon that authors will sometimes not mention the steps from a to f , but generally mention only the overall effect that is generated or produced in an effort to not needlessly confuse us lemmings. So was the O2 debt part of what you posted in the article or was that your assumption?
 
I think there is something to the article. for 3 reasons.

(1) Traditional HIIT routine contains significant aerobic component. It is "comparatively" (in terms of calories used from different energy sources) less aerobic than low intensity cardio, but it still uses up great deal of fat.

(2) But the problem here is that such "fat burning" (aerobic) activity not only uses up lots of fat, but it probably makes fat storage mechanism more efficient. Human body is always good at compensation -- it makes sense, because fat store would be necessary for another bout of aerobic exercise.

(3) Thus, to become more lean, one has to convince one's body that fat stores are unnecessary. Obviouly, for the reason cited above, anerobic exercise is not the best.
The most anaerobic form of activity requires one's exerttion to be _very_ short and intense -- which means mostly ATP and glycogen are involved. The rest period following the activity should only allow ATP replenishment, rather than fat use.

(4) Overall fat loss will occur, as long as one is in hypocaloric state over the relevant time period, so one should not worry about not burning enough calories via exercise.

====================================

It would be interesting to come up with a program based on this idea.
 
[b said:
Quote[/b] ]But the problem here is that such "fat burning" (aerobic) activity not only uses up lots of fat, but it probably makes fat storage mechanism more efficient. Human body is always good at compensation --
Click to expand...

That's interesting. Has the science suggested this recently?

I think the problem with this study is that it argues the opposite, that short-bursts is better because it burns more fat *during* exercise than longer. However, it seems that the study fixes the "intensity", so that the effort for short and long "intense" periods are about the same . . . which again is not how most people actually do HIIT.

From my experience, doing short-burst HIIT (*not* in the manner the study suggests) is indeed harder because your ability to sustain peak speed/intensity only lasts a few seconds. You rest just enough so the body can replace ATP, however your heart rate remains extremely elevated during the entire 20 seconds.

A popular HIIT protocol is 4 minutes warm-up, 4-minute HIIT and 4-minute cooldown. During that 4-minute HIIT, you do 8 "reps" of 10-second high, 20-seconds low.

cheers,
Jules
 
vicious

[I wrote]
>> But the problem here is that such "fat burning" (aerobic)
>> activity not only uses up lots of fat, but it probably makes
>> fat storage mechanism more efficient. Human body is
>> always good at compensation --

[you responded]
> That's interesting. Has the science suggested this recently?

Jules, you know well that I was speculating and there is no scientific evidence behind my statement about "fat storage mechanism becoming more efficient " :D

I wouldn't be surprised, though, if it were true.
 
Your speculation is incredibly, incredibly depressing. Will "normal" cardio make you fatter in the long wrong . . my god the horror . .
laugh.gif


cheers,
Jules
 
[b said:
Quote[/b] (vicious @ Dec. 02 2002,6:29)]During that 4-minute HIIT, you do 8 "reps" of 10-second high, 20-seconds low.
cheers,
Jules
Click to expand...
S#@T! I have been doing it backwards
crazy.gif


I thought 20 secs all out was overkill! (cool band BTW)

Are you sure that is right?
 
jules (vicious)

But at least it does make sense, right?

Marathoners need to have certain amount of fat reserve -- this is necessary, because, to run a relatively long distance they need dense energy source (fat). Of course, they cannot carry too much fat, because it will bog them down.

Given that body's adaptive process tends to optimize itself for particular trained tasks, it would not be surprising if the body "tried" to maintain optimum ratio of fat and glycogen (best for aerobics). My point is that the ratio is probably not zero -- some fat is needed.

The recovery process would eventually reflect the body's adapation. For long distance runners (or hardcore aerobic workout fanatics), the process would include an attempt by the body to restore some fat, such that the body can become optimal at long, sustained aerobic activity.

I am not suggesting that aerobics makes you fat -- I am just saying that, IMHO, aerobic exercise does not seem to me to be the optimal stimuli for becoming "as lean as possible." The fact that HIIT works better than slow cardio at burning fat suggests that activities which _directly_ targets fat cells maybe crude.

So, what can one do? My speculation is that by doing the activity which pushes one's body toward more anaerobic state, one can become leaner. By doing lots of anerobics, you are letting your body know that the support structure (fat cells) for aerobic activity is not that important Over time, our body maybe convinced, and let go of the fat, provided one is hypocaloric.
 
That's an interesting perspective on the process Virtualcyber. :)

I think marathon runners may be particularly suspectible to gaining fat (off-season track athletes) because A) their diet has traditionally been carb-heavy and B) they have much higher insulin sensitivity. The typically "emaciated" look (and general depressed immune system) suggests to me that their bodies don't use their fat stores efficiently, though again this could be reinforced by their carb-centric diet. This process reinforces a loop where it's possible that their bodies become extremely sensitive to storage, and to that extent, their fat cells become much more receptable to storage.

Now, I think HIIT, due to it being a much shorter, more anaerobic activity, causes some sarcoplasmic hypertrophy, causing a more efficient mobilization of nutrients, in turn boosting BMR. Because it overall uses less glycogen and burn less protein than extremely long aerobic activity, such an athlete would be less inclined to eat a carb-centric diet. Therefore, their glucagon levels would be higher than the marathon athlete, leading to more efficient usage of fat stores.

In the practical sense, it wouldn't so much point to aerobic activity causing more fat storage, but anaerobic activity leading to the physiological changes and encouraging an appropriate diet, which would lead to more fat usage.

Or something. :)

cheers,
Jules
 
"Just HST baby" -- If Austin Powers tried HST, thatz what he'd say.

> In the practical sense, it wouldn't so much point to aerobic
> activity causing more fat storage,

I agree with that. I didn't mean to say it "causes" more fat storage -- just that there is a bf% "limit" to aerobic activity and the body becomes adapted toward hitting that limit.

BTW, I'd like to point out that, even though long distance runners look emaciated, their bf is around 6-7%. Considering how little muscle they have, the bf% is not too good. In other words, fat / muscle ratio is high (which is what we'd want low).

> but anaerobic
> activity leading to the physiological changes and
> encouraging an appropriate diet, which would lead to more
> fat usage.

Another way to look at it.
 
That's anabolic baby.

[b said:
Quote[/b] ]just that there is a bf% "limit" to aerobic activity and the body becomes adapted toward hitting that limit.
Click to expand...

A friend of mine and I discussed this sometime ago. We suggested that, if you're at already a low bodyfat, normal aerobic cardio wouldn't be enough to lower bodyfat. One could do marathon sessions and use the caloric deficit to "will" themselves to a very low bodyfat level (and tissue cannibalization.) Or they could use anaerobic training to cause physiological changes (from temporary metabolic fatigue, i.e. lack of oxygen) which would increase fat utilization.

That said, it would seem that as long as you're relatively glycogen depleted, your body has no choice but to use either protein or fat as energy. Anaerobic training, such as HIIT, don't eat enough calories to burn away that much muscle . . . and it's the kind of stimulus which causes protein synthesis/recovery anyway.

So, from this respective, it may just be that anaerobic training becomes a more efficient method of optimizing fat/LBM ratios, as you get leaner.

Anyway, I concluded to my friend that GVT was the best way to get ripped! :)

[b said:
Quote[/b] ]Considering how little muscle they have, the bf% is not too good.
Click to expand...

The thing is many marathon runners run themselves into ketosis. They eat plenty of carbs afterwards (though perhaps not enough to replace 2-3 hours of continuous running) and very little protein.

cheers,
Jules
 
Wow, been a long time since anyone has posted in this thread. But I've been doing some searching on cardio and "fat burning" and ran across this and figured I'd enter my two cents.

I've been doing a bit of research regarding fat oxidation and exercise intensity. The overall consensus seems to be essentially what Jules said in the last post:

Highly conditioned atheletes (who, not surprisingly, have a higher AT) will reap the most benefits in terms of fat oxidation from HIIT. As for the rest of us, the rate of fat oxidation is higher with medium intensity workouts (65-80% of your AT [not MHR]).

Everyone has their own opinion of what works best. I do not consider myself a highly conditioned athlete. I workout 5-6 days a week, but only for an hour or so at a time. When I was playing baseball in college practicing and training 5-6 hours a day I would have considered myself a conditioned athlete, but, of course, this interpretation will be different for everyone.

One thing to note in my experience. A year ago I spent a month walking around Europe living off of a reduced calorie (matter of finance, not choice) diet of mostly carbs, but walked EVERYWHERE. In the course of a month I lost 15 pounds of mostly fat, another 5 in the 2 weeks after I got home. Of course, this is probably too fast and it took me a year, but I eventually gained it all back. Note: I was doing no physical activity.

In contrast, I have been running as hard and as long as I can on the treadmill for the last 4 weeks trying to cut. I paid no attention to my AT just thought the harder and longer I worked the better. I have lost a bit of body fat% but have had zero weight loss.

I intend to start working out at approx 75% of my AT for the next 4 weeks a see what the results will be. I'll keep you posted. :)

WOW, that was long.
 
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