Fat burning vs Running out of fuel

[Spunout]

I think you understand on one level, as you have given the correct advice, but you have mis-understood how our body works.....

Bicycling Medicine, Arnie Baker MD, page 17

Up to 300 Calories per hour from fats continuously. At higher intensities, an additional 1,000 Calories per hour from Muscle Glycogen and Blood Sugar.

Dietmar: Fat 300 Calories per hour. Glycogen Stores: 1,500 Calories of Intramuscular Glycogen(also suggests total 2,000 Cal including liver glycogen). But if we burn 1,000 per hour then you see that we approach the bonk if we don't top-up with carbs while training. A very hard 1 hr time trial can deplete all glycogen stores.

(taken in context from above source).

 

[xcmntgeek]

I'm a newbie 59 year old male riding seriously for 2 years. i've dropped 60 lbs (230-170). now getting into longer distances (40-50 miles at 18+/- MPH) i'm running out of energy. i need to loose another 10-15lbs. how do you keep burning fat without running out of fuel??

Eat more, and more often, while you ride and then less off the bike. Most cyclists (including by the sound of it a few in this thread) don't eat near enough on the bike. Then, they over eat when they get off the bike. Chow down 300-400 cals an hour by eating a little every 20min while riding and then decrease what you're eating off the bike by 15% or so and you'll be fine.

Justin

 

[2 old 2 go slow]

Eat more, and more often, while you ride and then less off the bike. Most cyclists (including by the sound of it a few in this thread) don't eat near enough on the bike. Then, they over eat when they get off the bike. Chow down 300-400 cals an hour by eating a little every 20min while riding and then decrease what you're eating off the bike by 15% or so and you'll be fine.

Justin

Sound advice.

If you starve yourself on the bike thinking you're losing weight you're only setting yourself up for an overeating session later on. Replenish the carbs (and all those other important nutrients) steadily.

Losing weight is simple: Consume slightly fewer calories than you expend over an extended period of time.

 

[poky]

ok just finished 80k ride using advise given with no problems. i had a 30k wind with guests to 50k too. i need to investigate target heart rates. average was about 140. thanks to all for the advise.

 

[Lonnie Utah]

ok just finished 80k ride using advise given with no problems. i had a 30k wind with guests to 50k too. i need to investigate target heart rates. average was about 140. thanks to all for the advise.

Nice work. So, how'd you do it?

L

 

[reflecto]

I'm a newbie 59 year old male riding seriously for 2 years. i've dropped 60 lbs (230-170). now getting into longer distances (40-50 miles at 18+/- MPH) i'm running out of energy. i need to loose another 10-15lbs. how do you keep burning fat without running out of fuel??

Well, that is a good question. By the way you have done excellent in 2 years time. Congratulations. When you run out of fuel, it means you need to eat more. I know that goes against your present undertakings, but you might have to wait longer to lose the fat I think. After all, it does take time, as you already know.
My sis is a dietitician. I will ask her what she thinks. i will try to find some info for you. In the meantime take care and don.t let the thought of not losing as quickly as you expect to take you away from cycling. Keep at it. You are an inspiration to me and many others as well. Keep up the good work. bravo.

 

[germanboxers]

I think you understand on one level, as you have given the correct advice, but you have mis-understood how our body works. We ARE talking about cellular reactions, because it's our cells that do the conversion of one energy source to the other. You cannot separate the two. When we exercise, we are always burning glycogen in our muscles. This glycogen is replaced by glucose in our blood. The glucose in our blood is replaced by converting fat and glycogen in our liver and other areas to glucose. All of this happens inside the cells. At low levels of exertion, our body can keep up with the replacement of glycogen/glucose by our fat cells. At high levels of exertion, it cannot.

I don't think that's entirely correct, Lonnie. Fat is broken down into free fatty acids and some muscle tissue can use this directly to synthesize new ATP for cellular energy. I believe "slow twitch" muscle is more able to do this and I think the heart's primary source of fuel for conversion to ATP is free fatty acids? The brain on the other hand can only use glucose for the synthesis of ATP. It's one of the reasons why bonking leads to light-headedness, among other symptoms. It is also why if we were to fully drain our glycogen stores, we would die.

Muscles do not use glucose directly as fuel, either. The only fuel that works is ATP (Adenosine Triphosphate). Phospho-creatine, Glycolysis, and aerobic mechanisms (Krebs cycle) all provide the raw materials necessary for ATP synthesis. Of course, each has different speeds, capacities, and efficiencies in this regard.

 

[wilmar13]

I am not an exercise physiologist, but in the book: Maximum performance for Cycling, the author specifically states that type 1 muscles burn 100% fat, type 2a muscles burn both fat and glycogen and type 2b muscles burn only glycogen. Is this totally wrong?

 

[germanboxers]

I am not an exercise physiologist, but in the book: Maximum performance for Cycling, the author specifically states that type 1 muscles burn 100% fat, type 2a muscles burn both fat and glycogen and type 2b muscles burn only glycogen. Is this totally wrong?

I always forget which fibers are which? I'm not sure if "slow twitch" fibers use 100% free fatty acids, but I'm pretty sure they predominantly do so. The heart muscle is a form of "slow twitch" muscle and I believe it uses free fatty acids almost entirely. On the otherhand, I believe pure "fast twitch" fibers can only (or at least predominantly) synthesize glucose (usually via glycogen). Any physiologists available to lend their brains to the discussion??

 

[wilmar13]

I always forget which fibers are which? I'm not sure if "slow twitch" fibers use 100% free fatty acids, but I'm pretty sure they predominantly do so.

Yeah type 1 are slow-twitch, but I don't have the book handy to look up how type 2a and 2b were classified... 2b are definetly fast twitch, but I forget if 2a were as well or if the author treated them as a hybrid since they used both types of "fuel".

 

[Dietmar]

Dietmar: Fat 300 Calories per hour. Glycogen Stores: 1,500 Calories of Intramuscular Glycogen(also suggests total 2,000 Cal including liver glycogen). But if we burn 1,000 per hour then you see that we approach the bonk if we don't top-up with carbs while training. A very hard 1 hr time trial can deplete all glycogen stores.

Interesting, thanks! But, that means that total time over which a cyclist can perform is severely limited. Even if we assume the 1000cal/h number U mentioned above (and, yes, that is a very moderate level of effort), then even at that level we have emptied our glycogen stores after two hours. If we continuously burn fat (300 cals/h) and take up calories through food or drinks (say, 500 cals/h, max), then this looks like we can maybe sustain less than 3 hours of a 1000 cal/h effort, and then we are essentially done, or we need to go down to as little as 800 cal/h. Which leaves me to wonder, how do the pros do those long Tour de France stages? Certainly, these guys must be burning more than 1000 cal/h. Even if they are somehow much more efficient with their energy, I cannot imagine top riders burning less than 1500 cal/h. With the above numbers, that leaves that racer about two hours of high-performance time, max. And then?

P.S.: Sorry, the first example above was nonsense, of course (the one burning 1000 cal/h; in that case, I can keep going for 10 hours)., but at 1500 cal/h, we still run into problems quickly.

 

[Lonnie Utah]

I don't think that's entirely correct, Lonnie. Fat is broken down into free fatty acids and some muscle tissue can use this directly to synthesize new ATP for cellular energy. I believe "slow twitch" muscle is more able to do this and I think the heart's primary source of fuel for conversion to ATP is free fatty acids? The brain on the other hand can only use glucose for the synthesis of ATP. It's one of the reasons why bonking leads to light-headedness, among other symptoms. It is also why if we were to fully drain our glycogen stores, we would die.

Muscles do not use glucose directly as fuel, either. The only fuel that works is ATP (Adenosine Triphosphate). Phospho-creatine, Glycolysis, and aerobic mechanisms (Krebs cycle) all provide the raw materials necessary for ATP synthesis. Of course, each has different speeds, capacities, and efficiencies in this regard.

You're right. I guess this is why I made a "C" in animal phys. I was talking about what the cells carry across their membranes and break apart into ATP. I should have been more clear. The point of my post was it the chemical reactions that "create" energy are taking place in the cells.