Nutrition - Energy

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.