Re: Fuel use in aerobic and anaerobic metabolism

[Connie DeJong <cdejong@cisco.com>]

It depends on the phase of your conditioning. I was taught to walk up hills to build up the hind quarters strength, until a point where the horse was in good condition. At that point I would attempt a steady trot until they slow on their own.  I rarely gallop/canter up hills, unless they are short and not too steep, I'm believe the lurching and lunging is too strenous on muscles and tendons. Once a horse is physically fit I'm sure a canter up isn't any worse than trotting, some horses are more efficient at the canter than the trot. You can always tell with a heart monitor. It takes more sustained energy for a horse to walk up a hill, so once conditioned we walk the downhills and trot up.  

C

At 05:37 PM 1/29/99 -0600, Lynette Helgeson wrote:
>So in layman's terms this is all saying that it is a good idea to vary
>your gaits when you ride including some bursts of speed such as up
>hills? So that when trail riders ride all day at a walk they are
>actually tiring out their horses more then if they would throw in some
>trotting, cantering and running up hills? We had an argument about that
>in our saddle club when we went riding in the Badlands. There are those
>in the club who think that in order to conserve energy and save on your
>horse that horses should always be walked up hill. I was under the
>impression from this list that cantering up a hill was easier for the
>horse. Now someone said that trotting up a hill is bad for the horses.
>So what is the best way to go up a hill on a ride to conserve on your
>horse and what is the best way for conditioning rides to condition your
>horse?
>
>Lynette
>
>Beth Glace wrote:
>> 
>> Hi Shannon,
>> Well, this is essentially true.  There are a few important points
>> that need to be understood.   If this is too basic a review, please
>> pardon me, but I'll try to back up a little and give a bit more
>> biochemistry.  Glycolysis is the process where glucose is converted
>> through a series of steps to pyruvate.  During the process 2 ATPs
>> [which yield energy] are produced per molecule of glucose and no
>> oxygen is needed, therefore this metabolism is called "anaerobic".
>> At the end of glycolysis 2 molecules of pyruvate are formed.  [Now,
>> here comes the "aerobic" part], IF oxygen is readily available and if
>> this metabolism is occuring in a muscle fiber that prefers aerobic
>> metabolism, the pyruvate molecules will continue on through the Krebs
>> cycle, producing 36 more ATPs.  However, if the work is occuring so
>> rapidly that oxygen can't be provided to cover all the energy needs,
>> or if the exercise is very forceful and therefore stresses the fast
>> twitch fibers, an excess of pyruvate will be formed which cannot be
>> cycled through the Krebs cycle.  This pyruvate then is converted to
>> lactate.
>> 
>> A small amount of the lactate diffuses out of the cell intact, & is
>> sent to the liver where it can be reformed into glucose [about 25%
>> of the lactate produced is disposed of in this way].  This glucose is
>> then used to maintain blood sugar and can be used for energy.  Some
>> of the lactate that remains within the cell will be used by the
>> mitochondria oxidatively to produce energy. So, some of the lactate
>> can be recylced for anaerobic metabolism [by reforming sugar] and
>> some will go to oxidative metabolism.   Lactate is a preferred fuel
>> for highly oxidative tissue, such as heart muscle.    In this way,
>> even submaximal exercise actually is producing quite a bit of lactic
>> acid, but it is being metabolized rapidly.  As workload increases so
>> will lactic acid production and eventually the body's ability to
>> metabolize it will be outstripped.  At that point lactate will
>> accumulate increasingly in the cell and in the blood, causing an
>> acidic environment that does not allow the enzyme systems to work
>> well, and exercise will become more difficult. If doing true
>> intervals, where there is a significant lactate accumulation, it is
>> essential that low intensity exercise be used between hard intervals,
>> such as walking or jogging,  rather than complete rest between
>> intervals:  the contracting muscles will use up some of the lactate,
>> and will allow for faster recovery for the next interval.
>> 
>> Have a good weekend,
>> 
>> Beth Glace, MS
>> Sports Nutritionist
>> Research Associate
>> Nicholas Institute of  Sports Medicine and Athletic Trauma
>> Lenox Hill Hospital
>> NY, NY
>> 
>> Shannon wrote:
>> <<<The next point that was new to me: during the section on energy
>> systems, she mentioned that in AEROBIC metabolism, the horse can use
>> carbohydrates, fats OR lactate as a fuel source. Her point was that
>> during anaerobic metabolism, the conversion of ATP to energy is
>> wasteful, and the leftover toxic by-product Lactic acid still contains
>> some energy which can be used during low-intensity aerobic effort for
>> fuel.  I must have been snoozing in Biochem.... I don't remember ever
>> hearing this.   If this is the case, would it be possible for our
>> endurace horses to go in and out of the anaerobic threshold, and
>> actually provide fuel for the "rest" periods (like in interval
>> training) with lactic acid once the horse replaces its oxygen debt?
>> Wow. Interesting.  Comments?
> 
Connie DeJong
Villa Montagne Equestrian B&B
28495 Big Basin Way
Boulder Creek, CA 95006
(831) 338-2174 (voice & fax)

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