The studies we've looked at recently suggest that horses taking in high
caloric diets prior to two hours of moderate exercise demonstrated lower
blood glucose post-ex than those which either fasted or took hay only. Why
would that happen?
Insulin regulates blood glucose--without insulin the blood would carry high
levels of glucose and clog up every small capillary in the body. Insulin does
not cause the excretion of sugar--lack of insulin does that. What insulin
does is move glucose from blood and puts it into muscle cells as glycogen.
Chromium speed up this process.
So, if we end up with a lower blood glucose at the end of two hours of
exercise, because insulin has sequestered most of the intake into muscle
cells, are we better or worse off as far as sustained athletic performance is
concerned? People from this group have tried glycogen loading and have seen
good results (some saw no results), so my vicarious experience tells me that
there is something wrong with the idea that lower blood glucose is always a
bad thing. We know that going into a high speed race we need an elevated
blood glucose in order for the CNS to allow maximum effort. But after 2 hours
of work, are we seeing a decrease in performance of those animals fed grain?
If not, then whose to say that a lower blood glucose at the point doesn't
indicate a beneficial response?
Let me give you a parallel example: It has always been assumed that lactic
acid was Public Enemy Number One when it comes to racehorse performance. The
higher the lactate, the more paralyzed the muscles become--that's the theory,
with significant support from the literature. A typical post-race lactate for
a Thoroughbred running 6 furlongs to 1 mile is 22mmol/L. Let's say this
effort is a poor one--the horse races last or next to last, fading
dramatically at the end of the race, as most Thoroughbreds do.
Let's say we have another race, and post race lactic acid is 40mmol/L. Where
does the horse finish this time--in the grandstand? No. He wins, after a
4-day glycogen loading protocol. I was astonished by this lactate number
because it predicts a horse that can hardly move--but here we have a winning
horse, bright-eyed and bushy-tailed, who went right on winning several more
times. This process has been repeated enough thousands of times that we know
it works. Liz Quesnel took one Standardbred from having $3000 in winnings on
her card to over $100,000 in four months with glycogen loading.
So, we have a case here where the result you'd expect from a scientific
measurement does not play out in the real world. And the results we've had
from this endurance group--those with the courage and curiosity to
experiment--also shows benefit, or no result, but no negative result, from
glycogen loading. Many of the people I've talked to in this group feed grain
to horses competing in endurance events within hours of the beginning of the
ride and report performance benefits from that.
So, for me, something's not right here. We're concluding that feeding a horse
grain on the day of the ride is going to result in poor performance. Does it?
Does any study show performance decrements from feeding grain prior to the
activity? If so, they would directly disagree with the human science and with
equine experience.
Here's another way to think of this problem: Insulin regulates blood glucose,
which is central to the survival of the central nervous system. When glucose
gets low, the brain and spinal column limit glucose uptake by the
muscle--pulling back insulin production while limiting muscle firings (called
central fatigue). If, on the other hand, the body is loaded with glucose and
glycogen (insulin pushes glucose into CNS cells as was as into all the other
organs), maybe the brain is saying, "Hey, we're loaded with fuel--don't worry
about shunting it out to working muscles."
This happens with ketone levels. As ketones become higher in the blood, the
CNS limits the number of firings of a muscle cell to a certain level of
depletion--say 50-60%. At that point the muscle cell shuts down and
performance begins to be compromised. Louisiana State, though, showed that
four days of corn oil loading prior to a race resulted in zero ketones and
better performance--because the muscle cells could burn most or all of their
fuel. The trouble with constant corn oil is that muscle cells become
dependent on fat, and it's not a racing fuel--but that's another story.
I don't know if the above hypothesis has any validity, but I would like to
know if any of these studies post-grain/exercise showed a decrement in
performance coinciding with the drop in blood glucose after 2 hours. Or has
that extra glucose been stashed away into places where it will do a lot of
good?
Recently, a veterinarian consultant for Equine Athlete suggested in a Q&A
that feeding a racehorse grain on raceday would not help because the effect
of the feeding would not be seen for as long as 18 hours. That was the old
theory--now we know that digestion of carbohydrate (grain) has an impact on
blood sugar within 15 minutes and peaks at about two hours.
Everybody has the opportunity to be wrong, but we still have some things to
learn here. I'd like more discussion, particularly about performance with
grain fed, or glycogen-loaded endurance horses
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