Check it Out!    
RideCamp@endurance.net
[Date Prev] [Date Next] [Thread Prev] [Thread Next]
[Date Index] [Thread Index] [Author Index] [Subject Index]

Fuel use in aerobic and anaerobic metabolism



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?



    Check it Out!    

Home    Events    Groups    Rider Directory    Market    RideCamp    Stuff

Back to TOC