Hello boys and girls!
Today we will be talking about the body’s energy systems; how they work, what impact they have on the body and what it means to train all of them when it comes to not only your health, but for sports performance.
So where does the body get energy from in order to perform work? Our body get its energy from 3 macronutrients: fats, carbohydrates, and protein.
In terms of the amount of potential energy that can be utilized, fat contains the most per unit weight (9kcal/g vs a typical carbohydrate which is 4kcal/g). However, it is also very difficult to break down fats in our body because the actual structures of fats are very rigid and also the sheer size of the molecule is relatively bigger. However, because fat provides the=e most amount of energy per unit weight, it is an ideal source of energy when our body requires large amount of energy but when it is not needed very quickly.
Carbohydrates on the other hand are relatively easy to break down in contrast to protein and fats. Carbohydrates are broken down into monosaccharides known as glucose. These glucose molecules are then stored as glycogen in muscle tissue. Now because it is easy for our bodies to break down glycogen and utilize glucose for energy, it is consumed rather quickly. Your body attempts to moderate the expenditure of glucose by tapping into triglycerides and sourcing its energy from various sources rather than relying too heavily on any single one.
Proteins are categorized into either essential or nonessential amino acids; essential amino acids are ones that cannot be synthesized by the human body. The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine (i.e., F V T W M L I K H). The eleven amino acids humans do synthesize are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. Proteins are usually the last resort for the human body to breakdown and be used for energy.
So in order for us to utilize food for energy, it must be broken down into what we would call adenosine triphosphate (ATP). When ATP is used during processes that require energy, a single phosphate breaks off from the ATP, and the resulting breaking in bonds releases energy for work. This process leaves us with a adenosine DIphosphate and a free floating phosphate.
So now that we have a very basic understanding of where energy comes from, let’s move onto the important stuff – how we use it!
So when it comes to your body’s energy systems, there are 3 different systems that operate simultaneously. Although different energy systems are used in different levels at different intensities it is important to remember that your body does not simply ‘switch’ from one system to another. Your body’s energy systems work in an overlapping fashion relying more on one or another depending on the type of activity you are performing.
First, our ATP-phosphocreatine system provides the most immediate source of energy because it taps into the relatively small stores of glycogen in the muscle tissue. This glycogen is converted to glucose which then provides the necessary ATP needed for work. This ATP is then broken down into ADP and a free floating inorganic phosphate. This free floating phosphocreatine is then joined back onto an ADP and the process repeats itself. The amount of time this energy source provides for is <30 seconds. A good example of this is running a 100m; if you pay attention to your breathing, you will find that you are able to run at max speed for almost the length of the 100m with very few breaths.
Second, the anaerobic-lactic (anaerobic glycolysis) system, like the ATP-PCR system above does not operate with the aid of O2. This too means that although this system provides energy relatively quickly, it cannot last very long and there must be a trade off for this lack of O2. This anaerobic-lactic system provides energy for moderate level intensity activities. Think of activities that last just a hair under 3 minutes – running an 800m, swimming 300m, etc. This system does provide the body with a larger pool of ATP to be used for work, however there is no such thing as a free meal. Glucose is still the main driver of this system in turning ADP into ATP. However you will notice that here, there is a new molecule called nicotinamide adenine dinucleotide (NAD), and NADH is simply when a hydrogen is added to it. Here it is important to note that NAD is a coenzyme responsible for taking a free floating Hydrogen to bring back to the glycolytic process to keep producing pyruvate. This pyruvate is combined with O2 later on in the process to be used in the Krebs cycle. Now here it get’s fairly complex in terms of biochemistry but we will keep it as simple as possible for the sake of time and to maintain your interest. Pyruvate here leads to two things: 1. it combines with coenzyme A to produce acetyl-coA which leads further down the rabbit hole towards krebs cycle 2. Pyruvate then undergoes lactate dehydrogenase whereby NAD gives a Hydrogen to pyruvate to produce lactate with a free floating hydrogen. This lactate is transported to the liver and the reverse process takes place, known as the Cori cycle.
It is important to note here that ‘At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased’ (Wikipedia.org , retrieved Sept. 30, 2015). That is why when you are running an 800m run, you are breathing very hard because your body is working super hard to provide O2 for energy knowing that it can only recycle the lactate so fast.
Lastly, the aerobic system. The aerobic system relies on a constant supply of oxygen to create ATP, hence the term aerobic. The aerobic system takes on most of the heavy lifting when activities are sustained for long periods of time (think of anything that lasts 4+ minutes). Now the duration of the activity has a direct impact on the intensity in which you can perform this activity. You will notice that if you sprint 100% right out of the gates in a marathon, you quickly find yourself slowing down in order to sync your breathing with your running. The availability and efficiency in utilizing oxygen is the biggest influence on how intense you can perform your aerobic work.
So now that you understand the 3 different energy systems it is important to know that when you are training – whether it is for a 10k, an obstacle course, a marathon, or 100m sprint – you must design each workout to serve a specific purpose. If you are going to the gym today, target a specific energy system and work on it. Think about what your goal is and how to change your workout accordingly to create the most effective and efficient workouts to get you there.
Well, we here at Fit & Fed hope you found this article helpful! See you all next time and happy training!
Team Fit & Fed