Re: RC: Energy expenditure on a ride

[Tivers@aol.com]

In a message dated 7/13/00 9:36:26 AM Pacific Daylight Time, 
ralston@AESOP.RUTGERS.EDU writes:

<< This ought to liven up the discussion for a while!
 I've been having a side conversation with ti regarding fuels for 
 endurance horses and, as usual, he stimulated me to do a bit of digging
 into the literature. Came up with some estimates (these are
 rough) that might be of interest to the list:
 
 It has been estimated that a horse expends 12.4 kcal per hour of fast
 trot/canter (and this does not include hill work or sand type footing) per
 kg of weight.
 Assuming the elite horses (500 kg combined horse/rider/tack weight)
 are covering a relatively flat 100 mile course at the 
 fast trot/canter mode (a little over 12 mph) in about 8 hours of travel
 time, they would expend 
 about 50 Mcal of energy. This is in addition to the 16 Mcal required for
 "maintenance". 8 ounces of pure carbohydrate provides 0.9 Mcal. 
 Total caloric content of muscle glycogen in a 1000 lb horse has been 
 estimated to be 15 Mcal, liver glycogen 0.6 Mcal, intramuscular
 triglycerides (IMTGs-
 fat stored in the muscle) is 18 Mcal.
 If you rely exclusively on glycogen, glucose from carbos and IMTG
 you would have to give over 16 eight ounce carbo doses during those 8 hours
 (1 lb per hour!) just to cover the exercise induced caloric expenditure.
 You probably do not
 want to totally deplete the glycogen stores, so the caloric deficit would
 be even greater.
 So adipose (fat) tissue calories (366 Mcal available in the average 1000 lb
 horse), 
 which could not be used in the glucose driven environment of the carbo
 charged horse, >

This fuel source would be inhibited, but not eliminated. 


> or protein calories from muscle breakdown, which would not be inhibited by
 the high glucose/insulin
 but would not be very desirable, or VFA (from digestion of fiber in the
 large intestine) utilization has to kick in somewhere. The VFAs are utilized 
via the 
 Emden-Meyerhoff and TCA cycles (the pathways used by glucose and glycogen
 during aerobic work), 
 which means their utilization would appear as carbo use in your RER (this
 is a measurement
 which reflects the type of "fuel" being used-fats have low RER,
 Carbohydrates have high).
 So, as Susan has so often said, both a good store (not excessive, however)
 of body
 fat and a gut full of good hay, grass or beet pulp may help carry
 our partners through those long rides-even carbo charged front runners.
 Food for thought.>

Certainly food for thought, as is the improvement in performance with carb 
supplementation during the ride, as we've now seen hundreds of times. As is 
the near-universal use of similar supplementation in elite human endurance 
athletes.

To bring you all up to date on this discussion, here is the original premise 
I sent out to Sarah and others:

New Hypothesis

One of the primary adaptations seen in longterm endurance conditioning is 
greatly increased mitochondrial use of intramuscular triglycerides. Virtually 
all of the fat used during endurance competition in humans comes from this 
already-stored and efficiently-converted substrate source.  Little, if any, 
fat in circulation is used as racing fuel when carbohydrate supplementation 
is being used during the race. And, of course, adipose tissue is the most 
costly of fuels to mobilize. 

So, the idea is to tune, through conditioning, the muscle cells and their 
mitochondria to efficiently seek out and burn intramuscular triglycerides. In 
order to challenge that fuel pathway, an overabundance of fat supply during 
the conditioning phase is counterproductive, so you train with a modest level 
of fat in the diet. 

Then, as you approach the competitive season, you load fat-perhaps for as 
long as 6 weeks. Essentially what we're talking about here is at least 
doubling the fat contribution to energy supply during this time. Since most 
of the fat-burning structural changes are already in place at this point, all 
we're doing here is loading intramuscular triglycerides and associated 
enzymes.  We do not pull back the carbs-what we're looking for is a temporary 
oversupply of energy-with the fat being deposited intramuscularly while carbs 
remain the primary circulating exercise fuel.

Then, perhaps 5-7 days prior to the first significant competition, we 
carboload, topping off muscle glycogen and CP supplies. 

Then, the night before, we pull all carbs, kicking in the fat-recruitment 
process, and we start the competition under that flag, with the first dose of 
carb supplement just before the start of the race. And we continue with carb 
supps throughout the race-and after. 


Why?

It is clear, scientifically and practically, that carb supps during an 
endurance ride dramatically improve performance-particularly in those horses 
"going for the gold".  

But carbohydrate is only the icing on the endurance substrate cake. Without 
the underlying supply of intramuscular triglycerides, stored carbohydrate 
fuel is quickly used up[--well, not quickly, but eventually-we've found that 
you can lope about 80K on carbs alone, after a starvation diet that "ripped" 
up to 200 lbs of flesh from the experimental horses (not my 
experiment!!!)-then carbo-loaded them for ten days prior to the trial. But 
80K was the max distance at moderate speeds and heartrates achieveable. And 
recovery from such work was slow and painful.  

That underlying triglyceride substrate base is the key to never having to 
worry about available substrate under a carb-supplemented high-output 
competition. It is the key to maintaining adequate glycogen stores-when the 
horse runs out of muscle glycogen and is relying on blood glucose alone, he's 
on a very fast downhill rollercoaster.   Very dangerous situation in a number 
of ways. 


How?

Now, that's the hypothesis. It seems logical to me, and worth a field trial 
or two. But there are many questions unanswered. For example, how do you 
avoid oxidative damage during fat loading? How does a shift to a primarily 
carb-based training diet to a fat loading diet affect digestion? What are the 
best oils for this purpose? How far can you go with this-what are the 
limiting parameters of the approach? And what is the best race-day protocol?  
These and other questions need at least tentative answers. 

And that's why I'm asking you to wrestle with this concept a little in your 
spare time.

Tom