Yes, in racehorses we find that there is higher lactate production with the
glycogen loaded horse. However, the horse exhibits improved racing
performance. In fact, at least one study has said that horses winning races
show higher lactate levels than the losers. The point: glycolysis ain't
necessarily "bad".
> Acute rhabdomyolysis ("tying-up") has been associated with high
carbohydrate diets for many years. Carlstrom (as reported by McClean)
proposed that high CHO diets resulted in the increased storage of
glycogen and an abnormally high rate of lactic acid production which
caused degeneration of the muscle cells...(then a description of a horse
in this study on a high carbo diet which tied up badly)...obviously,
there are factors other than diet involved in the etiology of the
disease, but it appears likely that high muscle glycogen may be
detrimental to horses already predisposed to "tying-up".>
The presence of lactic acid was also associated with tying up for many years.
However, it was found not to be causative. Horses predisposed to tying up
have perhaps a half dozen "detrimental" causative factors at play. We have
found that if we can just get enough solid exercise into one of these animals
for two or three days straight, the predisposition goes away--as long as we
keep up the daily fuel draw down.
However, this IS a study suggesting a relationship between tying up and
carbhydrates.
Muscle
> glycogen "loading" appears to be most successful when high CHO diets are
fed to horses following intensive exercise bouts which deplete large
amounts of glycogen from the muscle. The usefulness of this practice,
however, is questionable." End of quote.>
This author needs more experience with glycogen loading. I don't know how it
will work with endurance horses, but I can tell you he's dead wrong when it
comes to race horses.
>ME: From this, I derived (and maybe I'm wrong) that glycogen-loading may
be a problem in horses prone to tying-up, as many endurance horses are.>
I would propose that endurance horses don't tie up for the same reasons that
shorter-going athletes tie up--a completely different etiology--and that more
available substrate might actually mitigate the problem.
> I have no idea how this would affect a horse trying to tie up DURING a
ride.>
This is what I'm talking about. Prevention of tying up before the ride is a
matter of keeping exercise levels reasonably high--no days off prior to an
event.
>I also gathered that glycogen-loading would be of most use
following a protocol of intense exercise (in this study, it was 10 m/sec
for 14 minutes) that largely depletes glycogen. >
This is incorrect, at least in race horses.
> In the practical sense,
I can't see many riders galloping at 22.37 mph for 14 minutes nonstop
immediately before an endurance race. I may be overly conservative, but
I would be more concerned about causing lameness, not to mention putting
the idea that Galloping is Fun into my horse's head when control is
tentative at the best of times <g>.
2) The discussion on glycogen loading in Equine Sports Medicine, by W.E.
Jones, DVM, pg. 28. Please excuse me if I quote most of the passage, it
also contains a decent explanation of what g-loading is for those that
don't really know (more bang for the buck, so to speak):
Quote: "The concept of "glycogen-loading is based on the principle that
if the resting glycogen of a muscle is increased, the time to fatigue at
a given workload should increase, delaying the manifestations of
fatigue. Glycogen-loaded humans have exhibited 37% increase in
anaerobic performance. Glycogen manipulations are applied to horses in
the attempt to deplete glycogen stores by combining several days of
low-carbohydrate, high-fat and high-protein feeding with strenuous
exercise. This depletion phase is then followed by 2 or 3 days of
reduced work and high carbohydrate feeding ("repletion") in hopes of
increasing the glycogen load to a level above that at the beginning of
the program by a rebound "overshoot". These programs have succesfully
increased resting intramuscular glycogen contents in Standardbreds, TBs
and Quarter Horses. Unfortunately, subsequent performance by either
unchanged by greater muscle glycogen content or was decreased (Kline,
1981; Topliff, 1983; Topliff, 1985). In addition, training itself can
increase intramyocyte glycogen contents. The magnitude of this effect
is not known, but the aforementioned increases in muscle glycogen
contents may have resulted from the exercise regimens employed, rather
than from the high-carbohydrate feedings.>>
So far, no complaints--except that this work is dated (old).
> Drawbacks to the use of glycogen loading include the increased
intracellular water retention that accompanies high intramuscular
glycogen concentrations, increasing the likelihood of both dehydration
and overestimation of an animal's fitness (Maughan, 1981). >>
Again, old, and incorrect.
>In addition,
because of the glycogen depletion-repletion cycle is only effective in
those animals with muscle fibers that are "trained" to both store and
metabolize glucose rapidly and efficiently, there is a risk of
triggering exertional myopathy after the high carbohydrate
feeding-resting-supercompensation phase. Muscle stiffness from lactic
acid accumulation was linked to rapid carbohydrate metabolism (McClean,
1983).>>
This is the author's extrapolation of limited data. Our experience is that
you can encounter huge lactate production rates and have a horse bouncing
back for more the next day. It also helps to give a final does of the loader
within 1 hour of completion of the work.
> Uncertainty persists, however, concerning the role of glycogen
reserves in the onset of myopathies." End of quote.>
And this is where i think compartmental syndrome may apply. The solution:
significant work every day in those animals prone to pre-exercise tying up.
> ME: What I derived from this supports what was stated in Pagan's study
above. Although I will be the first to admit that some of this research
is more than decade old, I think it has at least enough merit to be
worth considering.>
Pagan has since had success with chromium loading--which is another way of
pushing carbohydrate into muscle cells--it's part of a decent glycogen
loader.
> I also note that simply training will increase
glycogen storage in the muscle (this is also supported elsewhere), so I
personally would prefer to increase glycogen through conditioning rather
than glycogen-loading, although the two are also not mutually exclusive
concepts, either.>
What it comes down to is, once you've done everything possible with
conditioning, what other techniques remain available to make life easier for
the athlete during competition?
>3) Conversation with Dr. Snow. I know, I know, this is simply his
subjective opinion, therefore I cannot supply citations to go along with
what he told me. However, I have included a passage from the lecture he
presented to the Equine Nutrition Society of Australia in 1991, as the
information was essentially identical, except that Dr. Snow also gave me
his OPINION that glycogen-loading may be more risky than are justified
for use in endurance horses. Please note that I said "risky", not
"deadly". For those of you unfamiliar with David Snow, he is a
veterinarian and equine exercise physiologist (his degrees are BSc(Vet),
BVSc, Ph.D. and MRCVS), and obviously one whom I respect very much (my
own personal opinion here).>>
Dr, Snow is incorrect in this case. Got to go to work at this point, but will
return to this point later.
Thanks, Susan, we're getting down to the nitty gritty here.
ti