The Five Biggest Contradictions in Fitness
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The Five Biggest Contradictions in Fitness

It’s no secret that when people contradict themselves, it has the effect of making the flaws in their actions or statements seem glaringly obvious. But what about when WE ourselves get caught contradicting ourselves by someone else?

By: Nick Tumminello Added: January 6th, 2014
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  1. #26
    Banned Allyrulez's Avatar
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    Aka laid the smack down

  2. #27
    Senior Member Ebu's Avatar
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    I know aka23 knows his stuff, its just that there was a LOT there, and it would have taken FOREVER to type it up.
    "Color outside the lines"

  3. #28
    Wannabebig Member Podium Kreatin's Avatar
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    a flaw, i believe, i see here is that ppl assume that BMR energy sources and muscle-tissue energy sources go by the same rules. they don't. ok, since there is a lot to quote, i'll just add to what i put:

    the ranking for energy source for BMR (resting metabolism, from non-muscle cells):
    aerobic glycolysis>fat oxidation>>gluconeogenesis. non-muscle cells do not use creatine nor are capable of anaerobic glycolysis

    the ranking for energy source for EXCERCISE (muscle cells):
    creatine phosphate>anaerobic glycolysis>gluconeogenesis (protein conversion into glucose)>aerobic glycolysis and oxidation>fat oxidation

    here is why excercise differs in energy usage than BMR

    BMR uses little fuel per unit of time, b/c of mitochondria. mitochondria can use oxygen and harness 16x the energy (ATP) from glucose than w/o mitochondria (muscle-cells), adn are capable of harnessing energy from fat. however, "oxidative phosphorylation" is very slow, b/c it involves the mitochondria performing "slow, controlled explosions" w/ the oxygen to harness the energy in glucose and fat. u can think of this as a "hot-potato" idea, where oxygen is passed from one protein to another, until it gets to the end. this involves many enzymes and is a lot of oxygen is used

    excercise, however, uses the skeletal muscles, which differ in composition than non-muscle cells. this includes: very little or no mitochondria (limited fat oxidation), capable of anaerobic processes, and low oxygen reception relative to other types of tissue.

    we can all agree that cardio can boost BMR, which is effective in burning fat. but, in terms of the cardio session itself, longer is not better. this is b/c aerobic processes (aerobic glycolysis and fat oxidation) are TOO SLOW for running and other excercises (muscle-twitch burns more energy per unit of time than anything else).
    from aka's website link
    It was concluded that protein is utilized during exercise to a greater extent than is generally assumed and that under certain conditions protein carbon may contribute significantly to exercise caloric cost.
    the thing about running before breakfast: our blood sugar is low at this point, and u "force" ur body to use fat and protein. but, u will lose protein, b/c our bodies always try to keep a steady level of blood glucose. however, u always lose protein when u are losing fat from excercise, b/c fat is always gonna be the least preferred energy source for excercise, right under protein.

    CLARIFICATION: i didnt' say that "cardio isn't effective in losing fat." i'm saying, the cardio session isn't effective in losing fat, and longer is not better, which was to answer the question of this thread. if u do cardio and lose weight effectively, it is more of the BMR energy usage, not the excercise energy usage. here's my summary:
    cardio is effective in boosting BMR, which will help lose fat and spares proteins. but doign longer cardio isnt' gonna do much better, b/c the longer cardio session itself isn't effective in burning that much more fat, and won't boost BMR that much.
    Last edited by Podium Kreatin; 05-23-2004 at 11:48 PM.
    "No one can completely believe that I am natural.
    The most important drug is to train like a madman
    -really like a madman
    The people who accuse me are those who have never trained once in their life as I train every day of my life."

    Alexandr Karelin
    Ten-time World Greco-Roman Champion
    1988, 1992, 1996 Olympic gold medalist

    current stats (10/19/03): 20yrs, M, 5'4 @160lbs, ~11% body fat
    lifted since march 2000
    occupation:MCB major @ uc berkeley

  4. #29
    Senior Member aka23's Avatar
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    Quote Originally Posted by Podium Kreatin
    the ranking for energy source for EXCERCISE (muscle cells):
    creatine phosphate>anaerobic glycolysis>gluconeogenesis (protein conversion into glucose)>aerobic glycolysis and oxidation>fat oxidation
    I think you are calling something similar to the order of energy production during maximal exercise "the ranking for energy source." During near maximal exercise (sprint portion of HIIT or weight training), the body first uses intramuscular stores of ATP and posphocreatine (PCr). At maximum intensity exercise, they are only the dominant energy source for about 7 seconds. After ~7 seconds, oxygen-independent glycolysis becomes the dominant energy source. In this process glycogen is used as fuel and lactate is generated. This energy process is sometimes called anaerobic glycolysis, suggesting that it only occurs when oxygen is not available, such as when one is out of breath while sprinting. It actually can occur whether oxygen is present or not. Lactate accumulation is more associated with effort and hormonal release than lack of oxygen. Within a couple minutes of maximal exercise (by this point pace is slowed down significantly), oxygen-dependent glycolysis becomes the dominant energy source. Lypolysis generates energy from fat and also requires aerobic conditions. It is not involved much during the work portion of short periods of near-maximal intensity exercise (It is involved in the rest/recovery periods between sprints.). However, several studies suggest that sprints may be superior to traditional cardio for fat loss. One such study is described at http://www.exrx.net/FatLoss/HIITvsET.html. As I described earlier, fat burned during the activity does not equal total fat loss. Total fat loss is more closely related to calorie balance.

    The above "ranking" of energy systems relates to short sprints of near maximal intensity exercise. Traditional aerobic cardio is very different. During aerobic conditions, energy is continually being derived from three main sources: fat, blood glucose, and muscle glycogen. Fat is being used at the start and fat is being used at the finish. The proportion of energy derived from fat is closely tied to intensity. In one study, GA Brooks found the following approximate ratios of energy derived from fat to carbs near the start of exercise at various intensities:

    Rest -- 65% Fat / 35% Carbs
    20% VO2 Max -- 60% Fat / 40% Carbs
    40% VO2 Max -- 45% Fat / 55% Carbs
    60% VO2 Max -- 25% Fat / 75% Carbs
    80% VO2 Max -- 0% Fat / 100% Carbs

    The final case at 80% VO2Max is the near maximal intensity case discussed earlier. Note that at the higher intensities, calories are being burned at a much faster a rate, so the maximum rate of fat oxidation occurs when far less than 50% of the calories are coming from fat. The graph at http://www.biochemsoctrans.org/bst/0...esolution=HIGH
    shows how rate of fat oxidation varies with intensity of exercise. The study depicted in the graph found the maximum rate of fat burning at slightly below 65% VO2 Max. If I remember this study correctly 65% VO2 Max correlated with ~75%MHR in this study.

    Other factors affecting the proportion of fuel from fat include exercise duration, dietary composition including recent meals, training history, environmental conditions, hormones/gender, and supplements/drugs. The paper at http://www.biochemsoctrans.org/bst/0...bst0311270.htm gives a good summary how these factors come into play and how fat oxidation is affected diet, aerobic exercise, and environment.

    Notice that protein is not mentioned in the discussion above. As stated earlier, protein is generally not a significant source of fuel in exercise. This makes sense from both an evolutionary perspective and a biochemical perspective. It does not make sense that the body would prefer using protein to fat as fuel in typical conditions, as your posts suggests. Protein stores are limited, and it does not seem logical that the body would evolve to catabolize large amounts of muscle in typical exercise. The process of using protein for energy is also waistful, compared to fat. Protein generally only becomes significant in extreme conditions, when carbs are not available and fat cannot substitute. This might include in the morning on an empty stomach. Liver glycogen is nearly depleted. It is used to supply fuel to the brain. Ignoring special situations like ketosis, fat is not an adequate substitute, so the body is forced to resort to protein. Another example, might be high-intensity exercise done in low-glycogen conditions. Fat cannot supply energy at a fast enough rate for high intensity exericse, so the body must increase the proportion of energy from carbs. If carbs are limited, the body is forced to increase protein usage. This final example is similar to the study I linked to earlier, which found 10% of energy derived from protein under condtions of nearly full glycogen depletion. These extreme conditions of the study explain the quote you listed above: "under certain conditions protein carbon may contribute significantly to exercise caloric cost." This is further supported from the paper I linked to earlier in this post,

    "the quantitative contribution of branched-chain amino acids to energy expenditure is usually minimal (<1%). Even in extreme conditions (i.e. prolonged exercise in fasted conditions) amino acid oxidation only represents a relatively small fraction of total substrate utilization (<10%)."

    I do not have time to address the other issues, such as the BMR (Basal Metabolic Rate) discussion right now. I may post more tomorrow morning.
    Last edited by aka23; 05-24-2004 at 02:32 AM.

  5. #30
    Senior Member aka23's Avatar
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    Quote Originally Posted by Podium Kreatin
    a flaw, i believe, i see here is that ppl assume that BMR energy sources and muscle-tissue energy sources go by the same rules. they don't. ok, since there is a lot to quote, i'll just add to what i put: the ranking for energy source for BMR (resting metabolism, from non-muscle cells):
    aerobic glycolysis>fat oxidation>>gluconeogenesis. non-muscle cells do not use creatine nor are capable of anaerobic glycolysis.
    BMR stands for basal metabolic rate. It indicates energy used at rest during processes such as respiration, digestion, and brain function. In resting conditions, most organs (muscle, liver, kidneys) use fatty acids as their primary fuel. The brain and red blood cells do not have the necessary mitochondria to use fatty acids as fuel, so they are forced to use glucose during resting conditions. The brain has a significant fuel requirement. It usually requires approximately 150g of glucose/day or ~20% of total energy requirement. When you wake up in the morning your liver glycogen stores are nearly depleted because the brain uses these stores for fuel (via blood glucose) while sleeping. As stated earlier ~65% of energy comes from fat and about 35% of energy comes from carbs during resting conditions. Most of this 35% carbs are used by the brain as stated above.

    Aerobic glycolysis is a process in which energy (ATP) is derived from glucose and oxygen. During resting conditions (BMR), fat oxidation is favored over aerobic glycolysis. Fat oxidation's major disadvantage is that cannot supply energy at as fast a rate as glycolysis, so as intensity increases and fat oxidation cannot keep up with energy demand, an increasing portion of energy is derived from aerobic glycolysis.
    Last edited by aka23; 05-24-2004 at 01:04 PM.

  6. #31
    Senior Member aka23's Avatar
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    Quote Originally Posted by Podium Kreatin
    excercise, however, uses the skeletal muscles, which differ in composition than non-muscle cells. this includes: very little or no mitochondria (limited fat oxidation), capable of anaerobic processes, and low oxygen reception relative to other types of tissue.
    There are several types of skeletal muscle. Type I muscle fibers have a high mitochondrial density and primarily use triglycerides (fat oxidation) for fuel. Type IIa also have a high mitochondrial density, but not as high as Type I. They primarily use glycogen as fuel and can function in aerobic conditions. Type IIb fibers have very low mitochondrial density and poor aerobic capacity. Recent research suggest that these fibers are not present in humans and only exist in animal models. Type IIx fibers fall between IIa and IIB. They are present in human models.
    Last edited by aka23; 05-24-2004 at 12:44 PM.

  7. #32
    Wannabebig Member Podium Kreatin's Avatar
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    i already mentioned what BMR was, but some thigns u said were incorrect; our brain uses glucose AND ketones, and our RBCs do not use glucose, it only uses BPG (bisphosphoglycerate, a waste product of glycolysis which is only used by blood).

    the quantitative contribution of branched-chain amino acids to energy expenditure is usually minimal (<1%).
    i didn't disagree w/ this, i'm saying that fat burning is less than protein, and this is always goign to be true for muscle cells.

    Rest -- 65% Fat / 35% Carbs
    20% VO2 Max -- 60% Fat / 40% Carbs
    40% VO2 Max -- 45% Fat / 55% Carbs
    60% VO2 Max -- 25% Fat / 75% Carbs
    80% VO2 Max -- 0% Fat / 100% Carbs
    this follows my "ranking" accordingly. as u rest (BMR), u prefer fat and some carbs as sources of calories, but as u excercise, u use very little fat, and prefer sugars (despite the rise in oxygen delivery)! this is why more cardio isn't gonna be better for burnign more fat, b/c fat burnign is relatively too slow.
    i also have to add that aerobic glycolysis and fat oxidation uses the same process in the mitochondria: they wil compete, and ur body will prefer to use oxidative phosphorylation (generation of ATP w/ oxygen) by burning sugar, b/c it diffuses into cells better. fats, again, require many conversions, before it can get to the mitochondria, where it is reconverted as acetyl CoA (fat in adipose-> fatty acid -> acetyl CoA -> blood -> muscle cell -> mitochondria, ithink )

    Fat oxidation's major disadvantage is that cannot supply energy at as fast a rate as glycolysis, so as intensity increases and fat oxidation cannot keep up with energy demand, and increasing portion of energy is derived from aerobic glycolysis.
    i can partially agree on u on this, but imo, aerobic glycolysis slows down too as anaerobic glycolysis rates go up. lets refer to the previous quote w/ the VO2 chart: that "100%" carbs include anerobic glycolysis.


    the body first uses intramuscular stores of ATP
    ur body cant' store ATP! once it is generated, it is used immediately, b/c it is very unstable (ATP-> ADP + Pi + energy). PCr is the only phosphate storage that ur muscles use, and it works by regenerating ATP from ADP (PCr + 3 ADP--creatinekinase--> Cr + 3ATP)

    Lactate accumulation is more associated with effort and hormonal release than lack of oxygen.
    how is this hormonal (which hormones are involved)? lactic acid accumulates in two ways that i know of: lack of blood flow away from the muscles (venous return by muscle contractions, this is why u have to warm down after running for a long time, and the liver is waht cleans out lactic acid, and this'll give u cramps if there's too much lactic acid in the liver), and lack of blood flow to the muscles.

    also, as long as u feel the "burn" from any excercise, u are generating lactic acid, b/c that burn is caused by lactic acid, so u can't tell me that aerobic respiration is gonna dominate over anaerobic glycolysis, b/c our bodies ONLy generate lactate when there is oxygen deficiency! and where lactic acid is present (via the burning sensation in muscles), then fat oxidation is not occuring, b/c that too, requires oxygen, adn aerobic glyolysis is gonna be preferred over fat oxidation, again, referring to the VO2 quote above.

    i mean, our bodies will PREFER IDEALLY to use oxygen for all processes, but this is not possible w/ muscle contractions, b/c muscle contractions demand the most ATP per unit of time, and our bodies must use less efficient mechanisms (anaerobic mechs) to generate a butt load of ATP.

    think about this analogy: if u want a 700hp/600lb-ft car to go 0-60 in 3 seconds, u need a V8 to burn a buttload of gasoline, w/ an (in)efficiency of less than 8% energy extraction (the horsepower u get is less than 8% of the hydrocarbon bond energy in gas, while 92% is released as heat, exhaust, and monoxide). u can't generate that much torque and horsepower w/ a fuel efficient gas-electric hybrid (where u can use more than 12% of the hydrocarbon bond energy in gas). of course, this is compromise, cuz if u are running away froma lion, then u gotta make sacrifices

    clarifications (again): i didn't say u won't do aerobic glycolysis during excercise, or almost zero. i agree that oxygen delivery goes up during excercise (via bohr effect), but i'm talking abour RELATIVE fuel source preferences. all sources of fuel will be burned at a higher rate, of course, but at differetn proportions.

    we seem to agree on BMR.
    "No one can completely believe that I am natural.
    The most important drug is to train like a madman
    -really like a madman
    The people who accuse me are those who have never trained once in their life as I train every day of my life."

    Alexandr Karelin
    Ten-time World Greco-Roman Champion
    1988, 1992, 1996 Olympic gold medalist

    current stats (10/19/03): 20yrs, M, 5'4 @160lbs, ~11% body fat
    lifted since march 2000
    occupation:MCB major @ uc berkeley

  8. #33
    Senior Member aka23's Avatar
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    Quote Originally Posted by Podium Kreatin
    some thigns u said were incorrect; our brain uses glucose AND ketones, and our RBCs do not use glucose, it only uses BPG (bisphosphoglycerate, a waste product of glycolysis which is only used by blood).
    The medline medical encylopedia at http://www.nlm.nih.gov/medlineplus/e...cle/003482.htm states
    “.Some cells (for example, brain and red blood cells), are almost totally dependent on blood glucose as a source of energy”

    The university biochemistry page at http://www.lsmsa.edu/MKhandoker/bioc...ct%20sheet.htm states
    “In addition to brain, glucose is also the most important fuel for the red blood cells and is normally obtained from the diet.”

    I am well aware that the brain can substitute ketones as fuel in special situations, such as ketosis or severe starvation. Note that I wrote: “Liver glycogen is nearly depleted. It is used to supply fuel to the brain. Ignoring special situations like ketosis, fat is not an adequate substitute.”


    Quote Originally Posted by Podium Kreatin
    ur body cant' store ATP! once it is generated, it is used immediately, b/c it is very unstable (ATP-> ADP + Pi + energy). PCr is the only phosphate storage that ur muscles use
    The muscle cells store approximately 6 mmol of ATP per kilogram of muscle (Noakes, 1991). This ATP can sustain about 1 second of sprinting (Noakes, 1991).


    Quote Originally Posted by Podium Kreatin
    how is this hormonal (which hormones are involved)? .
    Epinephrine (a hormone) infusion increases blood lactate levels, while norepinephrine (a hormone) decreases levels. http://www.ncbi.nlm.nih.gov/entrez/query.f...t_uids=97236534 . Several studies have found a close correlation between epinephrine and blood lactate levels. If "anaerobic" glycolysis was primarily dependent on oxygen levels rather than hormones, then exercise in low-oxygen conditions at high elevation would generate more blood lactate. Instead the opposite is true.

    I am busy at work now and do not have time to address the rest of the your post.
    Last edited by aka23; 05-24-2004 at 03:48 PM.

  9. #34
    Senior Member aka23's Avatar
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    “"the quantitative contribution of branched-chain amino acids to energy expenditure is usually minimal (<1%). Even in extreme conditions (i.e. prolonged exercise in fasted conditions) amino acid oxidation only represents a relatively small fraction of total substrate utilization (<10%)."
    Quote Originally Posted by Podium Kreatin
    i didn't disagree w/ this, i'm saying that fat burning is less than protein, and this is always goign to be true for muscle cells.
    The quote above from the paper "Modulation of carbohydrate and fat utilization by diet, exercise and environment" that you responded to says protein oxidation represents less than 10% of substrate utilization in extreme conditions involving prolonged exercise while fasting and less than 1% in normal conditions. You are saying that fat oxidation accounts for less than this 1% of substrate utilization in normal conditions and this is always going to be true for muscle? I have already provided many examples where this is not the case. For example Costill's studies of treadmill running at 65% VO2 max found fat oxidation accounted for 39% of the energy at the start of the exercise and 67% of the energy 2 hours later. If fat oxidation accounts for 67% of the energy, then it is the dominant energy source, certainly more than protein. The referenced paper mentions a study in which 90% of energy was found to come from fat during exercise. This fat oxidation is primarily occurring in the muscle cells. The referenced paper states, “At rest and during exercise skeletal muscle is the main site of oxidation of FA (fatty acids).”


    Quote Originally Posted by Podium Kreatin
    this follows my "ranking" accordingly. as u rest (BMR), u prefer fat and some carbs as sources of calories, but as u excercise, u use very little fat, and prefer sugars (despite the rise in oxygen delivery)!
    You ranked aerobic glycolysis highest in non-muscle cells at rest. The listed study found that fat oxidation was the dominant source of energy at rest, not aerobic glycolysis. You ranked creatine phosphate, anaerobic glycolysis, and gluconeogenesis highest for muscle cells during exercise. I did not list anything to suggest that these play a significant role during traditional aerobic exercise. The study found that fat was the dominant source of energy at the start of lower intensity exercise, and the proportion of energy from fat decreased as intensity increased. The proportion of energy from fat would increase significantly above all these values, if we compared later portions of the exercise. For example Bosch did a study at a very high intensity in which only 6% of energy came from fat oxidation at the start of the exercise. After 3 hours at this intensity, the proportion of energy from fat had increased by more than 7x to 43% Note that this fat oxidation was occurring in the muscle cells. Repeating the early quote, “At rest and during exercise skeletal muscle is the main site of oxidation of FA (fatty acids).”


    Quote Originally Posted by Podium Kreatin
    this is why more cardio isn't gonna be better for burnign more fat, b/c fat burnign is relatively too slow.
    Rate of fat burning increases significantly as duration increases. I have given many examples. Calories burned increases as duration increases, and calorie balance primarily determines fat loss, not fat burned during the activity.


    Quote Originally Posted by Podium Kreatin
    i can partially agree on u on this, but imo, aerobic glycolysis slows down too as anaerobic glycolysis rates go up. lets refer to the previous quote w/ the VO2 chart: that "100%" carbs include anerobic glycolysis. .
    Exercise at near-maximum intensities in which nearly 0% of the energy is derived from fat are the work portion of sprints that cannot be continued for more than a minute or two. These sprints are primarily dependent on the so called “anaerobic” pathways – ATP, CP, and "anaerobic" glycolysis. Fat oxidation and aerobic glycolysis are the primary sources of energy during traditional aerobic exercise, which occurs at a lower intensity.
    Last edited by aka23; 05-24-2004 at 06:24 PM.

  10. #35
    Wannabebig Member Podium Kreatin's Avatar
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    Rate of fat burning increases significantly as duration increases. I have given many examples. Calories burned increases as duration increases, and calorie balance primarily determines fat loss, not fat burned during the activity.
    i didn't say this wasn't true. i said, u will burn relatively less fat than any other fuel source, and that cardio boosts BMR, which THEN burns fat effectively.

    as u burn more fat, u also burn more sugar and protein w/ it. hence, longer cardio isn't "efficient" for burnign mroe fat (like the car analogy; u can burn tons of gasoline to yeild tons of energy (excercise), but only <8% efficiency. but if u drive at slow acceleration (BMR), u burn less fuel, but u have a higher yield b/c u allow more oxygen to go assist gasoline combustion. this is the same for excercise, b/c oxygen delivery increases up to a point, and that's it.
    so, think about this: most oxygen u use is for BMR, b/c that's the top priority. u burn "1800kcal/day" just by standing still all day, and the rest is other thigns liek excercise. if u run, do u think ur body is gonna take away significant amt of oxygen out of ur BMR? of course not, cuz then, u'll die running [this is why reptiles only can sprint, they can't run for that long b/c they dont' have that much mitochondria])

    The muscle cells store approximately 6 mmol of ATP per kilogram of muscle (Noakes, 1991). This ATP can sustain about 1 second of sprinting (Noakes, 1991).
    this ATP comes from creatine, its not like u "store" ATP b/c is not a storage molecule. if u consider a radioactively labelled ATP (w/ labelled phosphate), and inject it into a muscle cell, u can take a "snapshot" about 10 minutes later; ur msucle cell still will have "6 mmol of ATP per kilogram of muscle," but none will be radioactively labelled, b/c it won't be the same ATP that u injected ( the labelled ATP* will be hydrolyzed into ADP*)

    Epinephrine (a hormone) infusion increases blood lactate levels, while norepinephrine (a hormone) decreases levels
    Lactate accumulation is more associated with effort and hormonal release than lack of oxygen.
    that report said epi and norepi had correlation, but it didn't say it regulated lactic acid. u implied that the principle mech for controlling lactate were these two hormones, which was not what that report concluded. (u can inject nitrites or monoxide into the blood and ur blood lactate would go up too, and this DIRECTLY relates to lack of oxygen delivery, and doesn't involve change in hormone levels)

    even if adrenalin affects lactic acid is significant; u do not release epi and norepi during excercises such as cardio. hormones wouldnt' explain why ur muscles feel a "burn," b/c as i said, ur body prefers aerobic all the time, and only releases lactic acid when it needs to make ATP quickly b/c there isn't enough O2 going to the muscles (which is the case when u run)

    in terms of cardio, oxygen delivery goes up b/c of the elevated pCO2/carbonic acid detected by the brain and heart, and the medulla then triggers an immediate effect by changing breathing rate, and vagal stimulation of the heart. elevated pCO2 in the blood also triggers the bohr effect. however, despite the increased oxygen delivery, we still generate lactic acid! why? b/c oxygen delivery is insufficient.

    Fat oxidation's major disadvantage is that cannot supply energy at as fast a rate as glycolysis, so as intensity increases and fat oxidation cannot keep up with energy demand, an increasing portion of energy is derived from aerobic glycolysis.
    so, we agree our bodies prefer glucose over fat oxidation, right? this is why our bodies will burn protein as a source of glucose. however, the major disadvantage is NOT that the fat goes through a different pathway than aerobic glycolysis, b/c it DOES go through the same process.
    http://www.accessexcellence.org/AB/GG/Acetyl_CoA.html
    question: ok, so fat AND glucose in presence of O2 becomes acetyl CoA, so why is fat slower, when it yeilds 9kcal/g and glucose yeilds 4kcal/g in aerobic conditions?
    answer: b/c, the rate-limiting step is the conversion from fats to fatty acids. BUT, conversion of protein into glucose is very fast.
    http://web.indstate.edu/thcme/mwking/cori.gif
    look at this: lactate is converted back into glucose, and this uses a LOT of energy (6ATP to regenerate glucose?). despite it being horribly inefficient, u also generate a lot of glucose very fast! this is why protein conversion into glucose (glucogenesis) is higher than fat.

    remember that its not about inefficiency. BMR is about efficiency. excercise is "release tons of ATP as fast as possible, no matter what the long term cost is, b/c the long term effect is that u'll be eaten by the bear if u don't run far enough!"

    check this out: our bodies have all the enzymes it needs to convert 18 of the 20 amino acids into glucose. why? cuz, its fast. and its preferred during cardio over fat.

    fat metabolism, from what i've learned, not preferred b/c it is too slow. first, blood flow to adipose tissue (the cells that store fat) is very limited (this is why ur skin is cold). second, fat is hydrophobic and cannot be transported into the blood. ur body has a set of enzymes just for converting it into soluble compounds (fatty acids), and when it gets into the destinations, involves other enzymes to reconvert it into other compounds (acetyl CoA). it takes a long time to change the chemistry of a highly hydrophobic molecule into a soluble fatty acid. when u eat fat, it takes a long time to go into ur fat cells b/c of the same problem in its chemistry (bile, lipase, chylomicrons, etc. only to be converted back into straight chains when it arrives in the adipose). fat requires long range circulation to reach the muscles, but protein and glycogen (ur muscles do not use liver glycogen) is local, and stored IN the muscles.

    (yea yea, ur prolly gonna say, but fat cells are right next to muscle cells, its not that far, and circulation isn't that slow! BUT, remember why spot-reduction doesn't work...)
    Last edited by Podium Kreatin; 05-24-2004 at 08:11 PM.
    "No one can completely believe that I am natural.
    The most important drug is to train like a madman
    -really like a madman
    The people who accuse me are those who have never trained once in their life as I train every day of my life."

    Alexandr Karelin
    Ten-time World Greco-Roman Champion
    1988, 1992, 1996 Olympic gold medalist

    current stats (10/19/03): 20yrs, M, 5'4 @160lbs, ~11% body fat
    lifted since march 2000
    occupation:MCB major @ uc berkeley

  11. #36
    Wannabebig Member Podium Kreatin's Avatar
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    as for the ranking system, i may be off b/c i'm basing everything on memory, and one year difference in textbooks makes a lot of differences. but, i know for a fact that fat oxidation is the slowest in excercise
    "No one can completely believe that I am natural.
    The most important drug is to train like a madman
    -really like a madman
    The people who accuse me are those who have never trained once in their life as I train every day of my life."

    Alexandr Karelin
    Ten-time World Greco-Roman Champion
    1988, 1992, 1996 Olympic gold medalist

    current stats (10/19/03): 20yrs, M, 5'4 @160lbs, ~11% body fat
    lifted since march 2000
    occupation:MCB major @ uc berkeley

  12. #37
    Wannabebig Member Podium Kreatin's Avatar
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    ok, since there is a lot of quotes u'll quote me from to make ur argument, try to answer these qs:
    1) if low intensity cardio prefers fat as a usage of fuel, then why do we feel a burn in our muscles? fat yields more than twice as much ATP than glucose, so why would our bodies resort to anaerobic glycolysis, which only yields a measly 2 ATP? (remember, i'm talking about low intensity cardio)
    2) how come sprinting (high intensity) gives a big burn in the legs, if VO2 is so high (80%)? should'nt oxygen delivery prevent lactic acid production?
    3) why do ppl get sore muscles from low intensity running?
    4) why do ppl get sore from HIGH intensity running?
    5)why do ppl cramp up when they run long distances (low intensity) if, according to u, aerobic glycolysis and fat oxidation is the choice of fuel? (crampign is caused by too much lactic acid from lack of oxygen going to that muscle site)
    6) why do ppl's leg or butt cramp up when they sprint (not talking about charlie horse) hard (high intensity)?
    Last edited by Podium Kreatin; 05-24-2004 at 08:24 PM.
    "No one can completely believe that I am natural.
    The most important drug is to train like a madman
    -really like a madman
    The people who accuse me are those who have never trained once in their life as I train every day of my life."

    Alexandr Karelin
    Ten-time World Greco-Roman Champion
    1988, 1992, 1996 Olympic gold medalist

    current stats (10/19/03): 20yrs, M, 5'4 @160lbs, ~11% body fat
    lifted since march 2000
    occupation:MCB major @ uc berkeley

  13. #38
    Senior Member aka23's Avatar
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    Quote Originally Posted by Podium Kreatin
    u will burn relatively less fat than any other fuel source
    This statement suggests that you always derive a greater portion of energy from both protein and carbs than fat. Research suggests otherwise. One example is listed in the study at http://www.ncbi.nlm.nih.gov/entrez/q...t_uids=3967777 . It states,

    “With light prolonged exercise there is a progressively greater use of fat until it can contribute up to 80% of the total caloric expenditure.”

    If fat can contribute up to 80% of the total caloric expenditure, then conditions must exist in which more energy is derviced from fat than protein or carbs. I have referenced studies and quotes from texts that show this the case in post after post. I have explained logically why protein is not a significant fuel source under usual conditions and listed studies that support this. I see no point to repeat the same information over and over.

    Lets take an example of medium intensity aerobic exercise, the kind of exercise that you frequently see people doing at the gym. Do you have any evidence that implies more energy would be “burned” from protein than fat? A quote from a text book? A study? Any reliable source of real information? Lets take an example of low intensity exercise done for a very long duration. Do you have any evidence that fat would not be the dominant fuel source? Again reliable information, such as textbook or study. This does not include feelings of soreness or lactic acid burn. This does not mean chemical equations showing that fat burning does not provide "fast" (high-intensity exercise) energy, just a simple quote from a study or textbook that supports your statement.


    Quote Originally Posted by Podium Kreatin
    cardio boosts BMR, which THEN burns fat effectively.
    Again I am repeating the same information over and over. Lets look at how much cardio boosts BMR.

    The study http://www.ncbi.nlm.nih.gov/entrez/q...t_uids=2706222 found that
    “Average BMR in the control period was 5.91 (SE 0.39) MJ/24 h and was not changed with activity. There were no changes in OMR (5.71 (SE 0.27) MJ/24 h in the control) nor in SMR (5.18 (SE 0.27) MJ/24 h in the control), nor in BMR, OMR or SMR when expressed per kg body-weight, or per kg fat-free mass. 6. These results do not support the suggestions that there is a sustained increase in BMR following exercise that can usefully assist in weight-loss programmes.“

    The study http://www.ncbi.nlm.nih.gov/entrez/q...t_uids=3409854 found that
    “Aerobic exercise did not significantly stimulate the 24-h resting metabolic rate of either the post-obese (3 per cent, 50 kcal) or lean controls (2 per cent, 30 kcal), nor was there any significant stimulation over shorter periods “

    Again BMR not elevated much unless the exercise is done at a high intensity. Bahr found that moderate intensity exercise, like is typically done by persons at the gym only increases BMR by 12-35 calories.

    Lets say BMR does increase. Why does that burn fat more effectively than the cardio? If you burn glycogen during the cardio, then glycogen stores decrease. This signals the body to increase fat oxidation. The fuel mixture at rest is altered, so that more fat is oxidized and the limited glycogen is spared. Burning carbs during the exercise causes fat burning to increase after the exercise is complete. . It is not the possible, small BMR increase that burns fat, it is the calorie deficit.

    I do not see the point to wasting my time continuing this discussion and repeating the same information over and over.
    Last edited by aka23; 05-24-2004 at 09:31 PM.

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