No, the lower your heart rate during any activity, the better. That is why a sedentary individual's heart will beat 90-110 beats per minute at rest, but a highly trained runner's heart will beat the same number of times during a moderate workout.

oh now I see what you're getting at! The lower your heartrate is during exercise the better shape you are in. But you don't want to go for exercises that keeps your heart rate low, you want to get your heart rate up there when you exercise.

Sounds super hard!

So you're saying the body can convert protein to energy faster than it can convert carbs and fat? I think you have missunderstood; The "problem" with high intensity exercise is that your body won't be able to deliver oxygen fast enough to the cells, then our body has to start converting glucoses/whatever else to ATP (which is energy) without oxygen, this is a process which is not efficient (you get 2 ATP per glucose molecule compared to 36 if you're using oxygen. Anaerobic and aerobic metabolism respectively) and also leaves lactate acid in your muscles.

There's not a magical limit where you stat burning protein. But you're body will have used most of it's glocoses and glycogen in the muscles before it starts tearing from your muscles and fat (although though fat is kinda burned along side everything here)

EDIT:
wait a minute.. you first say it's not a myth that at 85% your body starts burning protein. Then you say that it's due to prolonged exercise... What exactly is your stand on this?

I'm not implying that the body can convert proteins more quickly. However, your body utilizes proteins even before you reach 85% of your max heart rate. No metabolic process is completely perfect, and proteins are used in very small amounts once anaerobic glycolysis begins. Generally, once your heart starts beating at rates around 80-85% of your heart rate max, it means that your body is beginning to strain itself in order to deliver fuels to muscle cells.

If your body maintains this pace for a prolonged amount of time, it cannot deliver the requisite amount of fats and carbohydrates to continue fueling such a high level of activity, and then utilizes a more readily available source of energy. I'm not say that all carbs/fats are now vacant at the cellular level, but the body begins increasingly using proteins because they are more readily available.

In the relatively short amount of time (6-10 minutes) it takes for an individual to complete a VO2 max test, it is common for a person to break the respiratory exchange ratio threshold for utilizing fats/carbs around 80-85% of their heart rate max at which point an individuals body begins to rely more heavily on proteins as fuels because the body cannot convert fat to energy quickly enough, the glycogen supplies at the cellular level have decreased, and because lactate build-up begins to slow carbohydrate glycolysis.

I was under the impression that it took more time to convert protein to energy than fat. And you are not implying, you are saying..

The heart beating faster has more to do with oxygen than nutritients anyways.

so let me understand you right. You're saying that at x heart rate, your body will stat using protein as fuel? do you have any science to back this up?

After 6-10 minutes the body won't even be done with the muscles glycogen stores (which is pretty much the quickest way to get energy) let alone carbs laying around. Or are you also saying that protein is quicker than carbs?

And yes, no process is perfect, but if protein is used that early, it's not used to a major extent, maybe a few molecules, but that's insignificant, it doesn't matter.

Why does protein get used once anaerobic glycolysis begins? And what's the difference in protein use between aerobic and anaeribic?

WHY is your body unable to " generate enough energy through fat metabolism " ?

What is the determining / limiting factor ? And why is 80-85% the threshold ...what happens at 80-85% ?

Can you elaborate ?

Just so I'm sure.

What do you mean by ' prolonged ' exercise exactly ?

Do you mean a cardio session of 20 - 30 minutes ( i.e HIIT ) ?

Or do you mean a cardio session of 45 minutes, 60 minutes ( i.e a 10k ) or 90+ minutes, 2+ hours in duration ?

And do you mean ' prolonged ' exercise at 80-85% and above or ' prolonged ' exercise below 80-85% as well - or both ?

Why would your body not convert the amino acids in your bloodstream into energy first ?

Before breaking down " muscular tissue " ?

I think everyone concedes that when doing ' extreme endurance ' cardio - i.e a marathon - there is a greater reliance on protein as a energy source than normal. No one would dispute that IMO.

But, I think the context of the ' myth ' in this case / post, has to to do more with someone who is going to the gym to do a simple cardio session on the treadmill. To me, that would be about 30 minutes and likely no more than an 1 hour on the treadmill IMO.

So, to me, the question is, if you run on a treadmill at 80-85% for 30 or 60 minutes, how much of your energy needed to complete that run - if any - stems from an actual breakdown of muscle tissue ?

Is 3% of the total energy needed to complete the run derived from " muscular tissue " ? Is it 5% , 10%, 15%, 20 % ?

At 80-85%....

- what % is from fats ?

- what % is from carbs ?

- what % is from protein ? ( and how is it's derivation split between amino acids in your blood and amino acids derived from tissue ) ?

[QUOTE=Karky;250766]I was under the impression that it took more time to convert protein to energy than fat. And you are not implying, you are saying..

The heart beating faster has more to do with oxygen than nutritients anyways.

so let me understand you right. You're saying that at x heart rate, your body will stat using protein as fuel? do you have any science to back this up?

Muscle glycogen (anaerobic glycolysis) is actually the second quickest form of energy production, following creatine phosphate metabolism. Most VO2 max tests do not last beyond 10 minutes, at which point the individual is exhausted to the point that they must void whatever is in there stomachs at the time, no amount of glycogen can keep up with that type of exertion because there is not enough oxygen delivered to the cells. Protein catabolism actually still only requires a relatively small number of enzymes (comparable to carbohydrates). However, just like lactic acid build-up from anaerobic glycolysis, there is a build-up of ammonia when proteins are catabolized. Unlike lactic acids, which require oxygen (usually in the form of water) to transit and leave the body through expiration, ammonia can be readily absorbed into the blood stream for "handling" in the liver. So the body is more likely, at the cellular level, to utilize proteins over carbohydrates when lactic acid levels are high.

All this begins to occur at around 80-85% of the heart rate max, at which point the oxygen deficit within the blood and cells exceeds the amount of oxygen that the body can respire into the blood stream from the lungs.

Even during moderate cardio exercise, 15 percent of energy is created through anaerobic glycolysis and oxidative deamination/transamination of proteins. Protein use is minor, but more than just a "few molecules."

Proteins and carbs are always being used, however, when the body begins to rely more heavily on anaerobic glycolysis/ protein catabolism (greater than 15% of the total energy production) it will first utilize carbs more heavily because they are easier to break down, until lactic acid build up slows anaerobic glycolysis and the body has to rely on protein catabolism for energy.

Most of this info is pulled from the text Human Physiology by Vander, Sherman, and Luciano, as well as my old kines exercise physiology notes (for which I unfortunately no longer have the textbook), and from Exercise Prescription 6th edition from the ACSM.

so lactate needs oxygen to to get out of the muscles? But ammonia doesn't, so your body will use protein since it can get rid of the waste more easily. That kind of makes sence, good info. However, I think it's kind of wrong to say at 80-85% of heart rate max the body will use more protein (even though it's common that anaerob glycolysis gets used at that point). I think you should rather say that once anaerob glycolysis is used and lactate acid starts forming in your muscles, your body will use more protein for fuel.

And about the ammonia thing.. I was under the impression that we sweated it out, creating that ammonia smell you sometimes get after exercise. I experience this if I do prolonged exercise, like running forever, 2 straight jujitsu practices, etc. I have, however, never got it from sprinting and stuff like that (which really builds lactate acid in my muscles)
I've also smelled it towards the end of a weight training session (in which I never felt any lactate acid)

There was some good info in your post, but I just don't know if it's correct or not, so I'll have to check that out.

The largest item here is your question about the 80-85% threshold. You can find this information in some of the ACSM or NSCA readings. At around 80-85% of the heart rate max, a person's lungs are not able to deliver enough blood into the blood stream to both keep up with oxygen delivery requirements, and then later, remove enough of the lactic acid build-up to prevent the slowing of the anaerobic glycolytic metabolism. The latter is actually a double edged sword, as slowing of anaerobic glycolysis also slows aerobic oxidation because the energy generated in glycolysis actually provides the initial energy required to start (and then sustain during exercise) aerobic oxidation.

"Prolonged" can depend on the fitness level and the overall genetic makeup (amount of white vs red muscle tissue, lung size, etc) of the individual.

For most common exercisers (moderate fitness levels), "prolonged" at 80-85% of their heart rate max can start at around 30-45 minutes, but it's not going to be the same for all individuals.

Don't have time to get to the rest of your points just now but I'll try to come back to them later.

Happy New years everyone!

Its not a matter of glycogen keeping up because it can, its the capacity to rid the lactate formed as a result. And you dont mention that protein utilisation if it did occur has to go through aerobic metablism therefore much slower. Lactate doesnt leave through expiration via water, it is actually a valuable source of energy which in the liver, the cell it was produced in, or other cells can easily revert back to pyruvate and therefore replenish or be used as energy. Your last sentence is to say the nicest, plain wrong.


Maybe read over your texts twice?



More accurate to say proteins are constantly being turnovered. Id like you to show me where you get this 15% protein use when 85% max.

The "lactic acid" (anaerobic glycolysis) energy system is only capable of providing energy for sustained exercise. After 2-3 minutes, this system falls off (going from providing 80-90% of all energy within the first couple of minutes to 5-15% during extended exercise greater than 3 minutes. Yes lactic acid is used for further energy production, however, during high intensity extended exercise greater than 3 minutes the body reaches its anaerobic threshold, where the blood cannot contain any more lactic acid. If anaerobic energy production does not slow, excess lactic acid must be removed from the blood by expiring it into the air. The same happens during high intensity (>80% of HR max) cardio in which there begins to be oxygen deficit, where the body can no longer produce energy quickly enough from aerobic oxidation. The body supplements by trying to increase energy production from anaerobic sources beyond glycolysis needed to maintain the oxidation. Again though, beyond 2-3 minutes, lactic acid build up will occur and shortly thereafter, individuals will reach their lactic acid threshold and will have to expire excess lactate (in which the body neutralizes the acid and the resulting compounds in the equation are water and CO2). This why, when measured, the ratio of CO2 produced to O2 consumed increases from the standard for fats (.7) to the standard for carbohydrates (1.0). With prolonged exercise, this ratio actually decreases as the body is unable to keep up with energy production from fats/carbs alone and begins to rely more heavily on proteins (an RQ of about .82).



It's simple exercise physiology that in most individuals, at 80-85% of their heart rate max, the body begins to rely more heavily on anaerobic energy systems (greater than the normal 15% that they deliver when working at lower intensities over greater periods of time. This is standard supported by many Respiratory Quotient (RQ), Respiratory Exchange Ratio tests.




I did not say that 15% of energy comes from protein. And granted the body is going to utilize free amino acids in the blood stream, but it will also use proteins and amino acids present within the cells, which involves muscular catabolism on some small level (and much greater levels during extremely long high intensity cardiovascular activity such as marathon running). I don't have exact numbers for the percentages, though I will continue to look for some.

Where did you get this whole expire lactic acid from? even though its actually lactate. If you got a reading of .82 that doesnt mean its burning mostly protein, if your confused about RQ then read over it again or ask a lecturer.
The way that the body actually neutrilises is through the various buffering systems i wont go into to. The H + can form with bicarb and is expired indirectly via co2, tha lactate doesnt get expired...its valuable energy!





Ok i see what you meant now..




same here..

Sorry that I did not clarify... a sustained RQ of .82 is the general value in identifying protein catabolism, but generally requires an increase to an RQ of 1.0, followed by the decrease to .82 with continued high intensity exercise. Just because an individual's RQ crosses .82 moving from .7 (fats) to 1.0 (carbs) and vice versa does not mean that proteins are a major contributor to energy production.

And yes, lactate does not get expired directly, and I apologize for oversimplifying and saying so... during the "lactate shuffle" generally 60-70% of it is converted to water and CO2 and expired with the remainder being converted to glycogen and protein and glucose.

So.. science guys, do you agree now? I gotta learn this stuff, so what's the short simple answer?

I do feel the need to say though, that while this info might be true, I think it's overthinking things in terms of training (saying I wouldn't NOT do high intensity exercise because of this, as it's probably not that big of a deal) I've heard that there's also evidence that lactate acid increases growth hormone production..