Horses that quit

["Beth Glace" <lb@nismat.org>]

Hi Sue,
The quitting described, just slowing down 
suddenly and refusing to "race" does sound like an energy source
problem.  As a matter of fact it sounds remarkably like "bonking" or
"hitting the wall" which is seen in humans during long duration
exercise.  Although blood sugar may be low, or may be low- normal,
blood sugar is not the fundemental culprit.  Blood sugar provides some
of the carbhohydrate for higher intensity exercise, but most of the
carbs are coming from the glycogen stored within the muscle itself.  
When this energy tank is depleted the exerciser must rely pretty much
entirely on fats, which are not preferred by the fast twitch fibers
and which is supplied more slowly.  When glycogen in the active 
muscle is gone, exercise intensity MUST decrease dramatically, 
typically to a walk or slow jog.  Glycogen is depleted more quickly 
when high intensity exercise is engaged in;  the scenario you 
describe fits this theory.  The horse is racing hard, is up-front, 
and then slows because it has blown through the available carbs.   
One solution might be to set a pace that the horse can maintain, 
rather than going out too hard.  Pace.  Pace. Pace.  Crucial in 
maintaining glycogen.  [I once described this to a friend who worked 
in marketing.  Her astute - and correct- interpretation was "oh, you 
mean when you run too fast you poop out early".   Well, yes.]

  The more fit the individual the less carbohydrate used for any 
given workload, just as more fit individuals will have a lower heart 
rate for a given speed.  Really fit horses can maintain those top 
speeds because they are using a higher proportion of fats, and less 
carb, to get the work done.  In humans, exercise at higher speeds can 
be greatly extended by giving carb during exercise.  Why?  Because 
you are giving an outside source of readily available energy as the 
muscle is contracting, thus sparing its own limited carbohydrate 
stores.  We, therefore,  provide sport drinks with a small amount of 
sugar in them to extend exercise.  Small amounts of sugar or sugar 
in water might also be an option for horses as long as it is given 
once the exercise has begun.  Although sugar does trigger insulin, 
exercise is a powerful suppressor of insulin, at least in other 
animal models, and typically can be given in moderate amounts 
during exercise with good results.  

    Probably the best solution to this problem is multifaceted:  
bring the horse into the event well trained, thus sparing the use of 
glycogen at any absolute work load;  make sure the horse is rested 
and "tanked up" the week prior to the race [well fed while 
exercise is tapered off just prior to racing = carbo loading], and 
hope that the horse eats well during the event; ride the horse 
according to it's ability and current level of fitness, pacing as 
evenly as possible.  As Heidi and Steph also mentioned low blood 
sugar may have been triggered by giving large amounts of sugars, 
particularly during a hold when insulin levels are no longer 
suppresed.  The insulin may kick in to lower blood 
glucose just as the horse is beginning to exercise, thus providing 
too much of a drain on blood sugar:  the result is called reactive 
hypoglycemia, as the levels drop well below normal.  


Just some thoughts,

Beth
and Klass Act


 <<This season I have seen quite a few horses "quit" on the 
trail. Nothing seemed to be wrong, they just stopped racing.  To my
knowledge, all of them eventually finished (some had 2 miles to go,
some had 25 miles to go) and none were treated.  All were experienced
trail horses, some were top contenders and the ones I saw were running
up front until "it" happened.   Any comments from the nutrition gurus
out there?  Any one else experience or see similar cases?  >>
Beth Glace, MS, CDN
Nicholas Institute of Sports Medicine and Athletic Trauma
Lenox Hill Hospital
New York, NY


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