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ENERGY
What is energy?
Well energy cannot be created or destroyed. It is the power that allows to do
things. Energy is categorised into many different types - such as heat, light,
kinetic (movement) etc. Essentially in many biochemical reactions, the energy
of the reactant is converted with very high efficiency into a different form.
In living organisms - in the furnace of the cell, the mitochondria, the free
energy contained in small molecules derived from food is converted into a different
currency - the free energy of Adenosine TriPhosphate (ATP). The chemical bond
energy of ATP is then utilised in many different ways. In muscle contraction,
the energy of ATP is converted by Myosin into mechanical energy. Membranes of
cells and organelles contain pumps that utilise ATP to transport molecules and
ions against chemical and electrical gradients.
The Citric Acid Cycle
The Citric Acid Cycle (also known as the Krebs or Tricarboxylic Acid Cycle)
is the final pathway for the oxidation of common fuel molecules - amino acids,
carbohydrates and fatty acids. Most fuel molecules enter the Citric Acid Cycle
as Acetyl CoA post the glycolitic pathway. The link between glycolysis and the
Citric Acid Cycle is the oxidative decarboxylation of pyruvate to form Acetly
CoA.
The rate of the Citric Acid Cycle is also precisely adjusted to meet the animals
cell's needs for ATP. ATP is an allosteric inhibitor of citrate xynthase. The
effect of ATP is to increase the KM for acetyl CoA. Thus, as the level of ATP
increases. Less of this enzyme is saturated with Acetyl CoA and so less citrate
is formed.
The Citric Acid Cycle only works under aerobic conditions.
Muscle Contraction
Muscle contractions begin with an electric signal from the central nervous system.
This current then arrives and immediately transfers up and down the length and
depth of the muscle through a relay system of tubules. When the message reaches
one of the thousands of receptor sites, it drops off a shot of calcium. Calcium
inhibits the noncontractile proteins tropinin and tropomyosin, which, until
the calcium showed up, had been doing their job keeping the actin and myosin
proteins separated. Calcium takes away all of the power that tropinin and tropomyosin
have in separating actin and myosin.
Further analysis reveals this process even more clearly when we look at the
sacromere, which is simply one unit of actin and myosin. At each end of the
sacromere is a rather broad anchoring structure called a z-disc. And extending
inwards from each z-disc are thin strands of actin that just manage to overlap
the much thicker strands of myosin that reside smack bang in the middle of each
sacromere.
Myosin protein strands have little receptor sites that emenate outward from
either side of their main bodies that resemble something of a cross between
little hooks and the strands of a feather. Technically, these receptor sites
are called cross bridges, as they serve to bridge across or connect actin and
myosin.
Once the electrical energy charge for contraction arrives via the nerve cells
from the brain to the muscle, the nerve cells drop off a little packet of calcium
that immediately severs the leashlike effect of troponin and tropomyosin. With
the leash removed, so to speak, several phenomenal actions take place involving
the now free floating actin and myosin:
The cross bridges rotate and in so doing draw the actin filaments and z-discs
inward ever so slightly.
The cross bridges begin to attach to the actin protein strands.
The proteins themselves undergo a change in shape.
The sacromere shortens as both z-discs are drawn inward.
When many of these sacromeres shorten simultaneously, the muscle fibres - and
then the muscle itself - contract. And, although some textbooks and internet
sites may tell you that the shortening of the sacromere is caused by the release
of energy caused by the breakdown of ATP (Adenosine TriPhosphate), this is actually
not the case. In fact, the process of contraction will occur automatically whenever
calcium enters the picture, thus inhibiting the restrictive functions of the
tropinin and tropomyosin proteins. ATP is required, however, for the cross bridges
to release and return to their 'resting' positions until they're required to
contract again. An example of this can be seen if you flex the biceps in your
arm. This is the result of thousands of contractions and (if you extend your
forearm) releases of the cross bridges, with the contracting portion precipitated
by the presence of calcium and the releases fueled by the energy generated by
the breakdown of ATP.
The Role Of ATP
So just what is ATP? Well, quite simply, ATP is the fundamental fuel for all
bodily functions. From walking across the room to contemplating philosophical
abstractions, ATP is the energy that runs the show. ATP has been described as
a miniature warehouse of energy, because quite simply that is what it is. ATP
is made up of three phosphate groups - oxygen, phosphorous and adenosine. The
adenosine is really a molecule to which the oxygen and phosphorous are bond
to form the chemical compound ATP - adenosine triphosphate.
When energy is required for muscular contraction, ATP is the first one out
of the blocks to provide it - usually breaking off one of the phosphate groups,
thus leaving ADP (Adenosine DiPhosphate). The result is that a good portion
of energy is released for immediate use by the muscles. (ADP cannot be broken
down further into AMP (Adenosine MonoPhosphate), by the muscles themselves;
but if needed, this can occur elsewhere in the body to create more energy for
movement.)
A well rested athlete with good supplies of ATP, typically a red meat eater
or a person supplementing with a creatine product, has roughly three ounces
of ATP in his or her body, available for conversion into usable energy. This
will be adequate to keep your muscle contracting for roughly three seconds..
So if a weight training set is going to last any longer than three seconds of
course you will need more ATP. So where does this come from? Well essentially
it comes from the energy transporter - a chemical compound called creatine phosphate
(CP).
When CP is broken down into its molecular components of creatine and phosphate,
the energy released can hook up with an ADP molecule and attach to it a loose
phosphate molecule to create a new ATP molecule. And the neat part is that there's
probably enough CP stored in your body to keep up this ATP conversion process
for a solid 10 seconds.
During the first 10 - 60 seconds of muscle contraction, energy is largely derived
from your anaerobic system (meaning without oxygen). With longer duration training,
your body will start to employ aerobic pathways to help with the workload. In
fact, after 90 - 100 seconds, the aerobic system is responsible for 50 percent
of your energy output.
Eating For Optimal Muscular Energy
Whilst carbohydrates, fats and protein can all be used as an energy source by
the body, there is a natural preference.
The primary energy source of the body is carbohydrates which are stored in
the body as muscle glycogen or as liver glycogen. This is obtained in the diet
from grains, cereals, fruits, vegetables and sugars. Typically, carbohydrates
should form the majority of the typical diet at around 50 - 60% of total calories,
when talking about supplying optimal energy levels for muscular contraction.
This is because the anaerobic muscle system burns solely glycogen as its training
fuel source. It is within the period after the first ten seconds of ATP supplied
energy and all of the way upto the 60 second mark that the anaerobic system
uses glycogen to manufacture its own ATP. After this time period the aerobic
system kicks in.
The second energy choice of the body is fats which are stored in fat deposits
mostly under the skin. Fats can be found in meats, fish, oils, nuts, diary goods,
and most processed foods. Fats come in two forms, unsaturated being the preferential
one to have in the diet. Fats should provide as little as 15% of total calories
in the diet.
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