Last month we talked about the three basic energy production mechanisms in your body. We also listed the sources of fuel for those processes: ATP, circulating glucose, glycogen
stored in muscles and in the liver, fat and in some instances protein. Having taken a good look at ATP, let's turn the spotlight on the roles of glycogen, fat and protein.
Recall that your body stores glucose as the polysaccharide glycogen. Glycogen is stored in liver and muscle. During the first few minutes of exercise most of the energy for muscle
contraction is derived from local muscle glycogen (which gets converted to glucose) and from glucose that's already circulating in the blood. As exercise continues, progressively
more glycogen from the liver is converted to glucose and is dispatched via the blood to the muscles. The longer and more intensely exercise continues, the more the glycogen stores
Glycogen breakdown is not your body's only means of getting glucose for producing ATP. Your body can also make glucose from protein and fat-or, more specifically, from amino acids
and the glycerine part of fat molecules. The process of manufacturing new glucose is called gluconeogenesis.
Gluconeogenesis exacts a price for the glucose it generates, however. It temporarily reduces the body's protein "stores." In extreme cases this can result in a significant
reduction in lean body mass, or muscle. As a bodybuilder you obviously want to restrict the extent to which gluconeogenesis contributes to energy production. Enter the concept of
protein sparing. Having sufficient glycogen reserves limits how much the body resorts to gluconeogenesis-and the breakdown of muscle-to provide needed glucose during prolonged
training. We' 11 talk about how to limit gluconeogenesis by maintaining sufficient glycogen stores in a moment.
Fat as an Energy Source
First, though, let's look at another way fat can act as a fuel for ATP production-a very important way, in fact. During prolonged aerobic exercise the major source of energy for
ATP production is a fat-based process called fatty acid oxidation.
Oxidation simply means to combine something with oxygen. So fatty acid oxidation is a process in which stored fat molecules break down and combine with oxygen.
Fat molecules are triglycerides- glycerine that has three long fatty acid chains attached. In the first phase of fat oxidation-called lipolysis- these long chains are snipped from
the glycerine. The fatty acid chains, which are no longer attached to the glycerine, are now called free fatty acids.
The free fatty acids then enter the component of the cells responsible for energy production, the mitochondria, courtesy of a special transport carrier, carnitine. Once inside the
mitochondria they are broken down into two-carbon fragments that bind to coenzyme A. The resulting combination is called acetyl-CoA, which readily enters the energy production process
to produce ATP.
A side note: Although both carnitine and acetyl-CoA are involved in fatty acid metabolism, research seems to indicate that you can't increase the amount of fatty acid metabolism that
takes place by ingesting either of these substances in supplement form. So both are probably ineffective for promoting fat loss.
Producing Fuel for Energy
Okay, back on track. All the energy production processes occur simultaneously during exercise; however, for prolonged high-intensity training sessions (or lengthy aerobic work) the
limiting factor is the availability of glycogen. When the body's glycogen stores are depleted, you have to stop training.
There are three things you can do to push back the limit imposed by availability of glycogen:
» Increase your glycogen storage capacity.
» Make sure your glycogen stores are full to capacity.
» Decrease the rate at which glycogen stores are depleted.
What can you do to increase your glycogen storage capacity?
Train! In fact, exercise itself appears to be the only way you can increase your glycogen storage capacity.
What can you do to make sure you actually store as much glycogen as you're capable of storing?
Eat right. That means making complex carbohydrates a large part of your diet. Your best bet is to follow the American Dietetic Association's recommendation for athletes and get 50 to 65
percent of your total calories from complex carbs.
How about decreasing the rate at which glycogen stores are depleted?
Again, the solution is training. En-durance training, specifically, has been shown to increase the contribution of fatty acid oxidation during prolonged exercise. With more energy being
derived from fatty acids, less has to come from glycogen. The body's glycogen supplies are thus spared and last considerably longer.
More on Lactic Acid
Taking a step back from all the different energy mechanisms and fuels, we see two basic criteria for prolonged training:
» Your body needs a constant supply of glucose for energy.
» Your body must deal with the inevitable buildup of lactic acid.
We've already discussed maximizing your glycogen stores. Now let's see what you can do to deal with lactic acid.
How quickly lactic acid ends your exercising depends on three things:
» Your buffering ability
» The vascularity of your muscles
» Your ability to tolerate allow pH
Can you improve your buffering ability?
Maybe. One of main buffering compounds in your blood is bicarbonate. You can increase the bicarbonate in your blood by drinking a solution of sodium bicarbonate (baking soda, right out of
the kitchen cupboard) and water. There is some research to indicate that taking bicarbonate prior to lifting may increase the intensity with which you can train before lactic acid production
shuts you down. Be forewarned, though, that the procedure has been known to give some athletes a whopping case of the runs.
Muscular vascularity also increases training endurance. If you have more blood vessels, more oxygen and glycogen can be delivered, and more lactic acid can be removed. Can you increase muscular
vascularity through training? Of course! You're probably already working to do so for the sake of appearance. In addition to any aesthetic value you may realize, the increase in capillary
density from regular lifting also increases your training endurance.
The ability to tolerate a low pH increases endurance also. For reasons that are not clear, bodybuilders who exercise consistently are able to tolerate levels of lactic acid in their blood
that nonbodybuilders cannot. High levels of lactic acid cause muscle pain and fatigue, and bodybuilders are able to withstand pain and fatigue more easily than non-bodybuilders can. Clearly,
being able to tolerate muscle pain and fatigue gives you an edge, allowing you to pump out more reps at a higher weight. The only way to develop this tolerance is through regular training.
This, then, is the physiological explanation for something you've known all along: If you train regularly, your ability to train at high intensity improves dramatically. This once again points
to the importance of being consistent with your workouts. Nutritional supplementation and dietary manipulation can give you a leg up in the muscular energy department. In the end, however, the
significant gains come from keeping at it and training hard!