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Thread: You can use fat for high intensity exercise? page 3

  1. #21
    Lukey's Avatar
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    good to hear you guys are having good results training fasted, also thats a very interesting link i will look more into that in detail. My main fear is just losing muscle because i train very intesntly (usually 20+ sets) so if i run out of muscle glycogen i would be interested in knowing if my muscle has to break itself down to convert to glucose, or if i could use stored fat for the energy needs. It would make a lot more sense that the body would use fat instead of having to break muscle down, the body is incredibly smart so i doubt it would just start breaking down it's muscles unless it absoultely needed to.

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    Quote Originally Posted by Lukey View Post
    good to hear you guys are having good results training fasted, also thats a very interesting link i will look more into that in detail. My main fear is just losing muscle because i train very intesntly (usually 20+ sets) so if i run out of muscle glycogen i would be interested in knowing if my muscle has to break itself down to convert to glucose, or if i could use stored fat for the energy needs. It would make a lot more sense that the body would use fat instead of having to break muscle down, the body is incredibly smart so i doubt it would just start breaking down it's muscles unless it absoultely needed to.
    Well with a bit of math you can figure on if your going to "bonk" or not. I would say no. In 20 sets or about 1 hour workout I don't see you going through more than 400-500 calories worth of glycogen 100-125g. Unless you are on the extreme low end of glycogen storage (which I doubt due to your exercise intensity) Then you should have that PLUS 50g or more to spare.

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    Quote Originally Posted by Lukey View Post
    good to hear you guys are having good results training fasted, also thats a very interesting link i will look more into that in detail. My main fear is just losing muscle because i train very intesntly (usually 20+ sets) so if i run out of muscle glycogen i would be interested in knowing if my muscle has to break itself down to convert to glucose, or if i could use stored fat for the energy needs. It would make a lot more sense that the body would use fat instead of having to break muscle down, the body is incredibly smart so i doubt it would just start breaking down it's muscles unless it absoultely needed to.
    Well with a bit of math you can figure on if your going to "bonk" or not. I would say no. In 20 sets or about 1 hour workout I don't see you going through more than 400-500 calories worth of glycogen 100-125g. Unless you are on the extreme low end of glycogen storage (which I doubt due to your exercise intensity) Then you should have that PLUS 50g or more to spare. Then again if your a 90lb fella then my estimates may be way off....I'm just going with "average male".

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    Lukey, How many times are a week are you training? Give me an idea of what these >20 Sets are? are you including warm up sets?

  5. #25
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    at the moment i am training 5x a week on 20 sets, thats 20 sets of 8-12 reps heavy weight. I am only training this hard at the moment because it's summer and i have lots of free time, when summer ends i will probably go to 3x weight sessions a week with 20 sets 8-12 reps. Neckhammer thats an interesting way to put it, i also doubt i would be burning through that many calories lifting weights so if i keep my carbs to 100g a day and have it after i work out i would probably replenish all that glycogen. Interestingly though, dr greg ellis says theres absolutely no need for glycogen and over time when you adapt fat goes into the muscles and is used in the same way as glycogen. It's really a shame there isn't more research into this.

  6. #26
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    It depends. Anything lasting 10 seconds or less is really not going to use too much glycogen, you will primarily rely on ATP directly with body fat recharging it between sets. If you don't recover enough or your sets last over 10 seconds, you will burn more glycogen. Now, with keto-adaptation comes glycogen sparing. There is an interview with Dr. Stephen Phinney on DietDoctor.com where he discusses glycogen sparing. Basically, you store half as much glycogen but you burn 25% as much so it is a net gain in glycogen availability. However, fatty acids cannot be used in the same manner as glucose in the way you are referring for a couple of reason. First off, what you are referring to is anaerobic glycolysis which occurs in the cytoplasm of the cell. As the name suggests, the process doesn't require oxygen so it can recharge ATP very quickly. Fat cannot be used to recharge ATP without oxygen, so in that respect there is no way fatty acids can serve as a replacement for glycogen, it's physiologically impossible. Now, perhaps the glycerol backbone could be used to make glucose, but that's gluconeogenesis which takes a ton of time and is probably only a factor in restoring glycogen after a training session. The second limiting factor is that fat must enter the mitochondria to recharge ATP which requires time. While it is true that pyruvate from glycolysis enters the mitochondria for oxidative phosphorylation, this is not an anaerobic process, it requires oxygen and therefore requires time.

    Personally, if my sets are limited to 10 seconds or less carbohydrates really aren't a concern to me as long as I'm getting full recovery or performing an exercise with different muscle group with partial rest. In other words, maybe a bench press with a 90 second break followed by a deadlift followed by a 90 second break and repeat. However, I would caution against doing high intensity metcons or lifting with partial recovery unless you are going to increase your carb intake. If you don't you may be putting yourself in a situation where you rely on cortisol for gluconeogenesis which is probably not something you want to do over the long term.

  7. #27
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    Quote Originally Posted by Lukey View Post
    Hey guys, i was under the impression we needed glycogen for high intensity exercise (eg. Weights and sprinting). But i just watched this video, where Dr Greg Ellis explains given enough time our bodies adapt and that fat can power muscle contractions.

    Fuel for Muscle Contrations gone over by Dr. Gregory Ellis - YouTube

    Does anybody have any thoughts on this? would my muscles be able to use fat for sprints and weightlifting now that i am fat adapted?
    In short, no. True high-intensity efforts will always require glycogen. However:

    1. A high-intensity effort, by its nature, will not be maintained for a very long time(and hence, the total glycogen burn isn't anything obscene)
    2. Given the moderate muscular consumption of glycogen, you don't necessarily need huge amounts of carbs to fuel this.

    Skeletal striated muscle - Wikipedia, the free encyclopedia

    Max intensity effort requires you to use your type 2 muscle fibers on top of your type 1. Generally what's going to happen when you train, is that you can strengthen your type 1 fibers, enhancing their maximum output, thus enhancing their ability to burn fat - and you can work at a higher rate before getting into the effort level that requires your type 2 fibers and requisite glycogen burning. But when you go beyond the capability of your type 1 fibers, you will start burning glycogen with your type 2 fibers.

    There's more to it than that - but the short version of it is that your body will never stop requiring glycogen for intense efforts - but unless you're doing something like trying for a personal record in a 10k or the like, you're not likely to burn through enough glycogen for it to be a major problem, even on a diet that doesn't have huge amounts of carbs.
    Last edited by jsa23; 08-21-2012 at 07:10 PM.

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    Ok good info guys. I think from now on i will train fasted and have a post workout meal with all of my days carbs (about 100g) so i restore all of the glycogen. I shouldn't have been worried about burning muscle as it looks unlikely i will completely empty my glycogen stores now i am fat adapted. Thanks for the replies

  9. #29
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    Training 24 hours fasted is ridiculous for performance. I hate to say it but this sounds more like working out for looks than for performance. No person truly looking for performance gains would train on such fasts.
    My posts are for information only, based on my own research and experience. It is not intended nor implied to be a substitute for professional medical advice. The reader should always consult his or her healthcare provider to determine the appropriateness of the information for their own situation or if they have any questions regarding a medical condition or treatment plan.

  10. #30
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    Quote Originally Posted by Lukey View Post
    Ok good info guys. I think from now on i will train fasted and have a post workout meal with all of my days carbs (about 100g) so i restore all of the glycogen. I shouldn't have been worried about burning muscle as it looks unlikely i will completely empty my glycogen stores now i am fat adapted. Thanks for the replies
    That would be a bad idea. Your body replenishes glycogen at a rate of about 3% an hour, with full replenishment about 36 hours later. Of course, that data comes from an average joe who is not keto-adapted so the numbers may be a little different but that's all the data we have. I would tinker with it individually as you may not need as many carbs as you may think. Your liver stores 100g but your muscles can store about 500g. Your body will fight to restore the muscle glycogen in the higher intensity fibers first even if you are doing some form of passive recovery. This will either come from lactate being recycled in to glucose by the liver or directly from liver glycogen stores. So, if you have full liver glycogen stores to begin with it should cover a chunk of what you burn. The easiest way to figure out how many g of glucose you burned would be to wear a heart rate monitor during your session and subtracting the calories burned from fat from the total calories burned and divide it by 4 to get a guesstimate of how many g of carbs you should consume over the next 36 hours. You are way better off taking the carbs over a longer period of time to prevent a large insulin spike. You should be fairly insulin sensitive post-workout so it shouldn't require a ton of carbs anyway.

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