Re: Fuel use in aerobic and anaerobic metabolism

[Lynette Helgeson <helgeson@lansford.ndak.net>]

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?