Re: one of your type discussions on ridecamp now

[Tivers@aol.com]

Michael forwarded this post to me for comment, so I'll wrestle with it. 
Forgive me, Beth--it won't be an attack--your thoughts are, as always, very 
good and very clear.

<< 
 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. >

Let me add that there is increasing regard for the concept of Central Fatigue 
under circumstances like those outlined above. One of the endurance horses I 
was working with recently "bonked" toward the end of a very hard test at 
110K. Just. Stopped. We took bloods on all the horses post race and this one 
had the lowest blood glucose of all, 57, and thereafter displayed a 41,000 
CPK--astronomical! Clearly, he had been burning muscle, and maybe was into 
malignant hyperthermia. Still, his low glucose would have thrown him into 
Central Fatigue. 

Central Fatigue is still being studied, but it appears that bothe muscle 
temperature and low blood glucose are two key factors. When the CNS feels 
threatened by low blood glucose, it shuts down muscle activity. .  
  
 >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.]>

Agreed.
 
  > 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. >

I would wrestle with you here. As usual, my best, most honest, most informed 
advice is: forget fat! If you're down to fat in a race, you're into metabolic 
quicksand. You're also burning muscle along with the fat.


> 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.>

Don't worry about insulin, either. It's your friend. It moves the glucose 
into the muscle as glycogen. Just focus on maintaining elevated levels of 
blood glucose and all else will follow.   
 
 >    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.>

Yes  

>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.  >

Timing is everything. You want to know your horses glucose response curve. 
Insulin responds directly to blood sugar levels. If there is no elevated 
blood sugar, there is no insulin production. However, most horses will 
demonstrate a peak blood glucose at 2 hours after ingesting a fast acting 
carbohydrate. If you delay refurbishing blood sugar much beyond that point, 
you'll find yourself in the middle of a sugar crash--with subsequent reduced 
performance. 

Again, dworry about insulin, worry about keeping an elevated blood glucose. 
The insulin is there for a purpose, it's not Public Enemy Number One. 
 
 
 >Just some thoughts,
 
 Beth
 and Klass Act
  >>

Love you, Beth.

ti


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