Fuel Sources

Robert West

Smartt/RST

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.

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Smartty

Steve McGregor

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

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Smartt/RST

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/...st_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...

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Smartty

Robert West

Smartt/RST

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.

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Smartty

Robert West

Steve McGregor

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).

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