HIIT Cardio vs Moderate Carido

WI

GQ on AS!
Just wanted to share with you guys some very good posts on HIIT Cardio vs Moderate Cardio. I personally like HIIT cardio and if I recall correctly so does DRveejay along with a few others. Just wanted to get some more opinions over here! Which do you prefer and why, ofcourse while on AS to limit any loss of lbm

Just doing a little pontificating... thinking about how everyone tells you to do cardio on an empty stomach...

The "theory" is that one utilizes mostly fat cal's by doing cardio in the AM since glycogen stores are at a daily low.

This belief is then inferred further by some (most?) to "one will lose more fat if cardio is done in the AM as opposed to some other time in the day," Basically, implying that 20minutes on the stair master, if done in the AM, will cause more over-all fat loss than if that same 20 min is done some other time.

There are two problems with this reasoning...

The most obvious, it violates the first law of thermodynamics.. Burning 500 cals on the stairmaster is burning 500 cals on the stairmaster, no matter when it is done.

Here is where most will say "yeah, but more of those cals are coming from fat instead of sugar when cardio is done in the AM.

However, if one really wants to get to the nitty gritty, let's say I do my cardio in the afternoon instead of the evening.. I'll even EXTEND the popular belief and say that 100% of my calories came from carbohydrate stores (obviously, this doesn't happen). Now, I eat my normal balanced carb meal. The carbs ingested will replace the glycogen lost during the cardio. The comparison in this hypothetical situation is the same person who has already done his AM cardio.. His glycogen stores (hypothetically) are rather full.. He is more likely to store some of the carbs as fat than am I since my glycogen stores are lower, albeit I am no further ahead of him since he has already expended a portion of cal's from his AM cardio..

In other words, I'm just restating the first law of thermo... The generalization is, if one eats 3000 cals and expends 4000cals, he will lose weight, no matter how the cals enter or leave the system. Physiologically, this isn't entirely accurate, as macronutrient profile (etc) will indeed play a role. However, for this discussion, let's assume we're talking about BBers with reasonable eating habits.

The second argument I have against the idea that "AM cardio is better" is a question on the validity of the "greater % of fat burned when glycogen stores are empty" statement. This goes hand in hand with the belief that "slower cardio=more fat loss."

(the following was adapted from BIOCHEMISTRY, Stryer)

Marathon runners consume about equal amounts of glycogen and fatty acids.. If their fuel came from fatty acids entirely, the 2hr run would take more like 6hrs. However, the glycogen stores in the body are not sufficient to provide energy for the race.. Low blood sugar triggers production of glucose (from amino acids) that is needed for such an event.

This is interesting since the aim of BBers is to lose fat without losing muscle.. This is why many won't do high intensity cardio.. However, when glycogen stores are low (as in the morning) it's reasonable to believe that the body will lose more amino's to gluconeogenesis than when the cardio is done another time.. How significant is it? Not very, in my opinion.. Just as the difference between fat loss from AM cardio compared to cardio any other time of the day is also not significant.

Credit to be given to Andy13 of Elitefitness.
 
You obviously didn't read the study I posted.
You say (guess) that "doing cardio in the morning on an empty stomach will yield no more fat loss than doing it later in the day"...
The study has shown quite the opposite: However, the subjects oxidized significantly more fat (94.3 kcal) when they exercised on an empty stomach than when they exercised 60 or 90 min after the meal (71.6 and 68.8 kcal, respectively) (P less than 0.05). ""

Exercising on an empty stomach increased fat oxidation by 32 % which is a significant difference...

The first law of thermodynamics says that the total energy of the system plus the surroundings is constant. The First Law is also stated as energy is conserved.

You can't really apply it on this issue, human body is just too complex for generalization like that..
For example, you can eat the same amount of calories, but split over a different number of meals with a different macronutrient ratio, and actually gain weight/fat in one case, or maintain or lose in another...
It obviously wouldn't be the same if you ate only three high carb/fat meals vs. splitting your caloric intake into six or more high protein meals...
Applying first law of thermodynamics in situations like this doesn't take into account the complexity of human body, influence of different hormones, macronutrient ratio, timing of meals etc. which obviously have a very important role.

It's true you would burn the same amount of overall calories, regardless of when the cardio session was performed, as long as the intensity/duration remained the same - that's where the law can be applied - as it was shown in the study (215-219 kcal)..

Then you say "if this were the case, marathon runners could never complete their race"

That doesn't make sense at all, just because fat oxidation was increased that didn't inhibit the trainers' ability to perform cardio.

Credit to be given to Haris of milossarcev.com


If you guys read through all this and want to see the studies on HIIT let me know and I will post them!
 
Some studies show no difference between the effect of high versus moderate intensity cardio on body composition & 24-h energy expenditure ...

Am J Clin Nutr 2002 May;75(5):818-26 Related Articles, Links


Effects of exercise intensity on cardiovascular fitness, total body composition, and visceral adiposity of obese adolescents.

Gutin B, Barbeau P, Owens S, Lemmon CR, Bauman M, Allison J, Kang HS, Litaker MS.

Georgia Prevention Institute, Department of Pediatrics, Medical College of Georgia, Augusta, GA 30912, USA. bgutin@mail.mcg.edu

BACKGROUND: Little is known about how the intensity of exercise influences cardiovascular fitness and body composition, especially in obese adolescents. OBJECTIVE: Our goal was to determine the effects of physical training intensity on the cardiovascular fitness, percentage of body fat (%BF), and visceral adipose tissue (VAT) of obese adolescents. DESIGN: Obese 13-16-y-olds (n = 80) were assigned to 1) biweekly lifestyle education (LSE), 2) LSE + moderate-intensity physical training, or 3) LSE + high-intensity physical training. The intervention lasted 8 mo. Physical training was offered 5 d/wk, and the target energy expenditure for all subjects in physical training groups was 1047 kJ (250 kcal)/session. Cardiovascular fitness was measured with a multistage treadmill test, %BF with dual-energy X-ray absorptiometry, and VAT with magnetic resonance imaging. RESULTS: The increase in cardiovascular fitness in the high-intensity physical training group, but not in the moderate-intensity group, was significantly greater than that in the LSE alone group (P = 0.009); no other comparisons of the 3 groups were significant. Compared with the LSE alone group, a group composed of subjects in both physical training groups combined who attended training sessions >or=2 d/wk showed favorable changes in cardiovascular fitness (P < 0.001), %BF (P = 0.001), and VAT (P = 0.029). We found no evidence that the high-intensity physical training was more effective than the moderate-intensity physical training in enhancing body composition. CONCLUSIONS: The cardiovascular fitness of obese adolescents was significantly improved by physical training, especially high-intensity physical training. The physical training also reduced both visceral and total-body adiposity, but there was no clear effect of the intensity of physical training.

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Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation

http://jap.physiology.org/cgi/content/full/92/3/1045

"It is concluded that exercise intensity has no effect on 24-h EE or nutrient oxidation."
 
Hhajdo, you of all people should know for every abstract saying one thing you can find one saying the complete oposite. I find I burn more cals when I use the HIT cardio program over the moderate type.

I wont go as far to say that it will work better for everyone, but it is really more effective for me.

I really get a great work out using the HIT technique
 
I don't doubt that HIT cardio is effective.
The authors of study 2 actually recommend HIT since EE is greater:

"At higher exercise intensities, total fat oxidation may be greater because EE is greater. In a practical sense, the amount of time that an individual devotes to exercise on a daily basis could be a limiting factor as to how much exercise an individual does. In this instance, if the desire is to maximize fat oxidation, then the prescribed intensity should be one that maximizes the total amount of fat oxidized and not one that maximizes the relative contribution of fat oxidation to total EE. Furthermore, the prolonged effects of exercise on nutrient metabolism must be understood before solid recommendations can be made on prescribing exercise intensity for body weight and body fat regulation. In light of these findings, we would suggest that the exercise program that best maximizes 24-h fat oxidation is one that produces the greatest amount of EE. Given that time is a limiting factor for most individuals, we would also suggest that, if the goal of exercise is to maximize fat oxidation to better regulate body fat mass, then exercise should be performed at the highest intensity that can be comfortably maintained. "

and:

"..We therefore conclude that low-intensity exercise does not promote greater "fat burning," as has been popularized among the lay press.."
 
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