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training vs. diet - LONG

Hi all, 
Since I am currently working on a proposal to study high(er) fat 
diets in human endurance athletes I thought I'd comment here on my 
impression of the literature.  It has long been accepted that low 
muscle carb stores limit the ability to maintain moderate intensity 
exercise.  It is also known that muscle glycogen can be increased by 
high carb diets.  Furthermore, carb just prior to or during exercise 
is well demonstrated to extend exercise time.  Therefore, endurance 
athletes have routinely been told to increase dietary carbs.

However, the effect of chronically high carb diets on exercise 
PERFORMANCE in ominivores [rodents and humans] is less clear.  Rowers 
fed a moderate carb diet did store less muscle glycogen but did their 
exercise performance was not affected [Simonsen]; similarly high carb 
diets increased muscle glycogen stores but did not improve exercise 
capacity in runners or cyclists [Sherman, Muio, Lambert].

A prime adaptation that occurs during endurance training is the 
improved ability to use fats as an energy source during prolonged 
exercise. However, high levels of dietary carb, chronically, foster 
adaptations which favor carb use during exercise.  So, since 
training [particularly long slow distance] serves to decrease carb 
use but  high carb diets promote carb use, it can be argued 
that long term very high carb diets could be counterproductive to 
endurance trained athletes.  This is probably particularly of 
interest to very, very endurance trained individuals who do much of 
their racing at a very submaximal level which depends heavily upon 
fat utilization [ultraendurance runners, Ironman triathletes and so 
forth in humans].  These athletes will still benefit from using carbs 
during the race as a means of sparing muscle stores of carbs and can 
thus extend their ability to exercise, but they may not need the day 
to day very high carbohydrate/very low fat diets that they have 
utilized in the past decade or so.

Yes, the studies I'm referring to are from human and canine and 
rodents models.  The racehorses Tom refers to are trained and 
raced at oxygen consumptions that are near maximal and as such 
are very heavily dependent upon carbohydrate use, so I think there 
may be real differences in the responses these animals have to fats 
in the diet as compared to endurance  horses.  

In regards to the fast horse querrie, I think you should probably not 
think first that the diet is at fault.  Perhaps more work in the 
dressage ring, and on the longe, discipling the sense of pace and 
roundness might be helpful?  The rushing implies to me a lack of 
control and of the basics that ringwork might provide.  Certainly 
doing an hour an day of mostly trotting in the sand of an arena would 
be good fitness preparation  and might reestablish the communication 
and basic "frame" needed out on the trail.  Perhaps for the time 
being you should do most of the trot work in the ring and then go for 
walks only on the trails to break the "rush" and "only one gear" 
mentality.  Just some thoughts,

Beth Glace
Sports Nutritionist
Nicholas Inst. Sports Med and Athletic Trauma
Lenox Hill Hospital

Heidi wrote:
Perhaps you should check with Dr. Valentine at Oregon State about
recent evidence that fats are having a glycogen-sparing effect in
racehorses--researchers are finding that fat-fed racehorses have more
left for that sprint to the post than their carb-fed peers.  She bent
my ear about it for about an hour, and sent me some great literature
on it--seemed like a lot of pretty respectable names in the field are
in on this stuff.  But since my practical experience is limited to
endurance, and since I'm just an old doc out in the field observing
horses and not spending hours sleuthing the literature, you should
likely ask Dr. Valentine about that yourself.>>

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