Fuel Sources

Discussion in 'Power Training' started by Robert West, Dec 27, 2004.

  1. Robert West

    Robert West New Member

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    I understand if you are doing a sub lactate effort your body uses predominantly fat as fuel. I have read that if you go above your sub lactate zone your body will use a different means of fuelling your muscles. I'm under the assumption that once your body starts to use this different source of fuel, that your body will not just switch back to using fat as fuel just because you reduced your intensity. If this is true would I be better served to do my sub lactate efforts first then do my harder intensity efforts near the end of my workout or am I separating my workouts to dedicated hard days and sub lactate days. I would like to mix them as there is not enough time in a week to fit in everything.
     
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  2. Smartt/RST

    Smartt/RST New Member

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    You would need to be a little more specific about just what you mean by "sub-lactate" effort, however, there is a direct relationship between exercise intensity and the mix of fuels your body is using (also effecting "the mix" is what you eat before and during your workout, caffeine, the duration of the workout, environmental temperature, altitude, your fitness level and your sex). Fat, however, is not the predominant fuel source for exercise unless you are really crawling along, have been riding for at least a couple hours and have not taken in any carbohydrate during your workout. Even at moderate intensities (i.e.: around the lactate threshold - or 1mmol above resting - or an intensity which can be maintained for 3-6+hrs for trained cyclists using good nutritional practices) your primary source of fuel is carbohydrate.
    I'm not sure what you're getting at with "this different source of fuel", but this is not an issue that should be the primary factor for determining how you go about your daily training.
    BTW, not sure why this is on the "Power Training" forum.
     
  3. Steve McGregor

    Steve McGregor New Member

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    In order to provide a power based context to this, in general, in trained individuals, there is a 50/50 mix of Fat/CHO at an intensity of approxmately 65% VO2max. If we accept that the lactate threshold (depending on definition) occurs at 80% VO2max, then, CHO becomes predominate energy source above 80% of threshold (MSS, FT, OBLA etc...). So, I'm not sure if this is "crawling along", but it is certainly a power output that can be maintained for hours. So, Michael is right, fat is typically not the predominate energy source during moderate to high intensity exercise. An important thing to consider though, is that, as we approach the threshold level of intensity, the contribution of fat toward energy generation (or conversion) drops precipitously (both on a percentage and absolute basis), and the contribution from muscle glycogen increases exponentially. Therefore, this is something that does need to be taken into consideration on a daily basis, as resynthesizing muscle glycogen becomes more important following a workout performed at threshold or above, vs the converse.

    To the original poster, with regard to how to structure your workouts, you could come up with valid arguments for either approach. The first thing to consider would be, how best to simulate your racing. The second would be, if there are too many things to cram into your time constraints, you may need to think about cutting some things out, and focusing on the things that give you the most bang for your training time buck.

    Steve

    P.S. Happy belated Boxing Day for those of you in the Commonwealth
     
  4. Smartt/RST

    Smartt/RST New Member

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    Well, if indeed there is a 50/50 mix at 65% of VO2max, then CHO will be the predominat fuel souce at any intensity over that. This is somewhat a matter of semantics, but I do feel that it is important to not underestimate the role of CHO during even moderate exercise...here's a good review: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=1936083 (not for you Steve! I know you know).
    Steve does make a good point about replenishing glycogen stores on a day-to-day basis (this is always important). I intentionally used the word "primary" in my previous post as there are many other factors that determine how to set up a training schedule, such as those Steve mentioned. Next time I'll try to tie up the loose ends better...
     
  5. Robert West

    Robert West New Member

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    Thanks Steve for trying to clarify. Let me try to explain myself more clearly as I think Michael Smartt needs me to be very specific. First according to what I've read in Joe Friel's book, "The cyclist training bible" on page 36 it states that while riding at an aerobic state your metabolic system uses fat and to a lesser extent carbohydrates for fuel. I'm thinking anything below your lactate threshold (meaning that your bodies lactate has not risen) your body will predominantly use fat as a fuel. So when you reach the point at which your body's lactate increases by 1mmol your body relies mostly on carbohydrates for fuel. Now if you were to reduce your effort your body will not just switch back as easily as you turned your effort off. With that said my question is; would one want to train at a power, if you will, that is less than your lactate power as you will train your body's system to use fat if that is of any importance anyway. If that makes sense then one might want to train at a 5 minute power level after they do their sub-lactate power efforts. This may not be the most appropriate place to post this question, next time I'll post this type of question in the appropriate forum as I see this practice is not taken lightly.
     
  6. Smartt/RST

    Smartt/RST New Member

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    Robert, it certainly was not my intent to discourage your posts or be snide, I was just confused by your not mentioning how your question applied to the use of power or power meters....wasn't sure if you forgot something or if I was missing something.
    And yes, I did/do need you to be specific about your question, as the terms used to describe physiologic phenomena are often grossly taken out of context and given inappropriate meanings (an issue I'll stay away from here, it's just that the answer to your question greatly depends on it).
    As I mentioned earlier, the *primary* driving force behind the fuel your body uses is the current exercise intensity; this is regardless of what you have done previously (what the actual % of fat vs CHO is at any given moment will depend on other factors as well that I mentioned in a previous post). There will be a short delay in returning to a sub-LT fuel mix following high intensity exercise (your 5min power level efforts would certainly qualify) while the body catches up with the aerobic demand/debt, clears lactate and works to return to its normal pH, but this is temporary. There are certainly other factors at work here, but suffice to say, your body will generally return to using fuel in a sub-LT manner.
    I think that is good and appropriate to be asking your question and thinking in the terms you are, but I wouldn't let this issue drive how you plan individual workouts, there are things to be gained by using different approaches, mixing it up, training specific energy systems, specifically mimicing your event, etc.
    Hope this helps.
     
  7. Robert West

    Robert West New Member

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    Thx for your response Michael, no worries. I was hoping to find out how long it would take for your body to switch back. As for mimicking a race scenario in my training, even at lower intensities this time of year just doesn't seem to connect with my sense of logic. It seems to me I would gain more by working on my base (sub-lactate work) and maintaining my strengths by doing intervals although to a lesser degree than what I was doing during the season. I'm just trying to find my way by asking these types of questions. I have been coached prior to this, but I feel I would like to try it on my own this year. I guess I always think I know better.
     
  8. Steve McGregor

    Steve McGregor New Member

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    Dude, why you leaving me out? LIke Andy needs somebody pedaling his wears off of wattage anyway;)

    The reason I stepped on your post is that I just wanted to attach some numbers to your reply, since, I knew, in essence, what you were saying, but that some others might not. It's not really semantics, but rather what your definition of "crawling along" is (Well, I guess your right that is a bit of semantics).
     
  9. Smartt/RST

    Smartt/RST New Member

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    Oh, I just meant that I'm sure you are well aware of the info in that abstract....but I thought that might be good for an inside joke...glad you got it! :D
     
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