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El_Mac stupid question of the week

I’ve recently started doing morning cardio after eating a tin of salmon and drinking a cup of coffee.


I’m showing VERY good results. But, all this time spent sweating away has resulted in some questions.

When the machine says that I’ve done X number of calories, does that mean that I’ve done X amount of work or that my body has burned X number of calories? They’re not the same, since my body is not 100% efficient at transfering food to work. I need to know this for my post-cardio supplementation.

The second question is regarding the percentage of fat burned to glycogen burned. I’m not doing HIIT. My heart-rate goes up to 180ish. I can always breathe through my nose (ie. no gasping). I’m currently assuming that it’s 50% glycogen. I’m guessing there’s no “easy” ratio, but there might be?

Finally, does caffeine alter the Fat:Carb ratio burned? I know that it causes release of FFA into the blood stream. I’m just hoping that increasing my caffeine dose will allow me to reduce my carb intake post-cardio. Thanks for your help.

Yes, caffeine cam increase the amount of fat utilized during exercise because it makes fatty acids more readily available to energy convertion. However the rules of the energy pathways still exist! If you use an exercise intensity requiring energy faster than fat oxidation can produce, you’ll burn less fat.

But overall, yes, caffeine helps burn more fat during cardio work.

Christian already hit the caffeine issue, so I’ll tackle tht 50% one.


For your first question, I am going to go out on a limb and assume that the machine is using indirect calorimetry equations by simply taking the MET value at which you are working and the body weight you punched in. Unfortunately, this doesn’t take into account your BF%. As such, it’s not all that accurate a measurement. Better estimations are based on more expensive direct calorimetry protocols such as respiratory exchange ratio.


As for your second question, 50% is a very arbitrary figure. Percentages of calories burned from fat and carbohydrate are functions of diet, exercise intensity, exercise duration, and training status. The better trained you are, the less intense the exercise will seem (lower oxygen consumption in relation to your V02 max), and the more fat you will burn as a percentage. However, at greater intensities, you’ll burn more total calories (from both fat and carbs) during and after the session. As such, HIIT wins out every time!


Hope this helps!

In regards to the calories burned issue, Eric brought up the point about how body fat percentage is not taken into account. I don’t think that this is a major issue, because you do have to support your whole body weight during exercise (assuming it is weight bearing). As for something like stationary cycling, body weight does not matter as their is a specific energy cost for doing a certain amount of work.

And yes, the readout is saying how many calories you burned.

As for the breakdown of carbs/fats that are burned, their is really no way to know without hooking you up to a gas analyzer as Eric already mentioned. What I can tell you is that you burn what you eat. If you have more fat in the diet, you burn more fat during exercise and if you have more carbs, you'll burn more carbs.

As exercise intensity increase, the aerobic fuel mixture stays pretty much the same up until lactate threshold. On top of the aerobic fuel mixture, you wll add some more carbohydrates into the mix that are being used anaerobically. Based on your intensity described, you are below lactate threshold, so my best estimate of your CHO/FAT ratio would be to look at the percentages in your diet. Remove the protein calories and then see what percentage of cals come from fat and carb. Your aerobic metabolism should be fairly similar.

Jason makes a very good point (one which I overlooked). The standard indirect calorimetry equation for any activity is:

Calories per minute= (METs x 3.5 x BW[kg])/200


According to the “ACSM’s Guidelines for Exercise Testing and Prescription,” however, “the intersubject variability in measured V02 may have a standard error of estimate (SEE) as high as 7%. Since the equations are often used to predict V02, it is important to remember that the variance of a predicted value is much larger than the SEE (i.e., the prediction interval is greater than the confidence interval).” Furthermore, “these equations are appropriate only for steady state submaximal aerobic exercise. Failure to achieve a steady state results in an overestimation of V02.”


Okay, here’s my beef with that. We know that calories per minute are partially derived from a MET value, which is derived from V02. We know that V02 can be GROSSLY over- or underestimated based on factors such as gait abnormalities, wind resistance, holding hand rails while jogging on a treadmill, etc. Now, anyone who has been in the iron game for ten minutes or more knows that muscle burns calories than fat at rest. Don’t you think that this same effect, even if we’re only talking RMR (and not incremental calories burned), carries over to exercise and also counts as one of the complicating factors?


And, let’s not even get going on the fact that one would assume that those at lower body fat percentages are more trained, and thus reach steady state more easily. Most overfat people take much longer to overcome the initial oxygen deficit at the onset of exercise. If you’re trying to figure out how many calories are burned in a twenty minute cardio session, yet you’re spending 10 of those minutes in non-applicable oxygen deficit, the sample equation is useless for half the exercise session. The machines that you are using assume that you just magically jump right into a steady state. As such, they’re more accurate for fit trainers in this regard, yet still pretty inaccurate overall. What was my point again?

Well, thanks for not pulling any punches on the science! I must admit that other than what you guys have written (here and the past), I’ve never read anything on this topic. What’s MET?

Most of my calories come from fats. I guess that’s why I’m showing such excellent results from re-introducing cardio into my routine. I do know that I’ll really “run out of steam” after a couple days if I don’t get enough carbs (like, when I read on vegetable packets that they had Xg carbs per serving, and I assumed they meant usable carbs. Now I have to back-calculate based on calories per serving), so I’ve got to be using a fair number of carb pathways still.

Anyway, it looks like I’m over-consuming carbs post-workout. Can anyone think of why that might be a seriously bad idea? I’m still consuming fewer calories than I burned (er, 50%).

Eric, you said that overfat people have trouble overcoming oxygen deficit (or something like that, I can’t have your messages open while I reply anymore). Does that mean that they become winded quickly, quickly exhausting oxygen capabilities? Or does that mean it takes them a longer time (training wise) to develop endurance?

Finally, it strikes me that HIIT consumes more glycogen calories during the workout that non-HIIT. It’s rumored to burn more fat calories over-all. But wouldn’t this be because

a)your body is a bit “drained” of carbs and needs to use an alternate source.

b) HIIT causes some eccentric stress that needs to be “healed”?

I’m just thinking that the studies that compared HIIT vs. non-HIIT (and deduced that HIIT burned more calories per day) didn’t give their subjects post-workout carbs which would significantly halt my two points. I’m sure I’d prefer to have my energy available for the work-out I do later in the day.

Again, thanks for all the replies.

Note to T-mag. Is there any chance we could get a “preview message” option. I’m thinking it would really help close italics and close bolding.

You know, I didn’t think this was a stupid question…as a matter of fact, it’s brought up a interesting discussion.

When I say overfat people take longer to reach steady state, I’m referring to the comparison to “fit” individuals. Basically, the more well trained you are, the more efficiently your aerobic bioenergetic pathways function.

Also, you said that you are “over-consuming carbs post-workout” and asked if we could “think of why that might be a seriously bad idea? I’m still consuming fewer calories than I burned (er, 50%).” Unless you’re getting really fat (which I know you aren’t), chances are that you aren’t over-consuming! People with normal carbohydrate-rich diets still need to replenish carbs post-training, but you can probably tolerate even more because you’re functioning on lower carbs (thus leaving more glycogen “room” for those post-training carbs than those who are only partially [30-40%] depleted).

Part of the reason that HIIT burns a lot of calories is that it creates a large oxygen debt during the exercise that must be paid back at some time. Typically, this occurs after a workout as your breathing, heart rate and other markers still stay elevated for some time.

Mainly, it's just a matter of burning a bunch of calories. HIIT forces you through bouts of high intensity work, whereas some people have a tendency to take it easy during traditional cardio. Either one can do the job and depending on the case, one may be better than the other.

It just occurred to me that I never answered you “What is a MET?” question (I don’t know why this just popped into my head). I was in a rush and didn’t have the time to type it out when I first read it. I hate to think that you’ve roaming the streets completely confused about such an important issue:) Here goes:


You’ve probably seen the abbreviation VO2 before. VO2 is the volume of oxygen (O2) consumed per kg body weight per minute. Obviously, the harder you’re exercising, the more oxygen you’re consuming. As such, different exercise intensities and modes are given different VO2 values. VO2 max (also known as your maximum aerobic capacity) is the absolute most oxygen your body can consume. Some of the pulmonary rehab patients with whom I’ve worked have an estimated VO2 max of 7-10ml O2 per kg body weight. Last I heard, Lance Armstrong was in the neighborhood of 96ml O2 per kg.


Now, MET means metabolic equivalent. Basically, one MET is equal to 3.5 ml O2 per kg per minute, which also happens to be resting VO2. The need to express the energy cost of exercise in simple terms led to the MET classification. As such, we can express the energy cost of exercise as a multiple of resting energy expenditure. For example, the MET value for intense free weight training is 6 METs. So, in theory, your body is consuming six times more oxygen while you’re lifting that when it is at rest.


To calculate the O2 requirement of an exercise with a predetermined MET value, use the following equation:


VO2=(MET value x 3.5ml O2 per minute x BW in kg)


Then, multiply that value by the duration of the activity in minutes to determine the amount of O2 consumed for the whole session. I should note that all measurements will be slightly off because of the time that is needed to reach steady state.


Hope this clears it up!

Thanks Eric. That was impressive if all this was typed from memory. It strikes me that you guys must be doing quite a bit better in your classes vs. the average student because you seem to be living your studies full-time.

When I was learning chemistry, I would study and go to class. I wasn’t going on the web, chatting with people about it, using details to improve my life, etc. I wonder how many students live their studies vs. how many just put in the time at school?

You’re right. It’s the sad truth, but not nearly enough people in my field of study practice what they preach. It’s always good for a chuckle to look around at the people having Pop Tarts and Mountain Dew for breakfast, though:)