Fundamentals of Human Nutrition/Energy systems

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14.2 Energy systems[edit]

14.2.1 Anaerobic[edit]

There are three main energy systems that occur in the human body in order for muscle cells to regenerate ATP during physical activity; anaerobic is one of them, and includes the lactic acid cycle. During this cycle glucose is broken down into pyruvate. The goal of this system is to produce ATP at a fast rate for high-intensity exercises; these exercises last anywhere from five seconds to two minutes (Whitney). Anaerobic translates to lack of oxygen. Examples of anaerobic exercises done during an anaerobic exercise test, by Dr. Henry Vandewalle, include force-velocity tests, vertical jump tests, staircase tests, and cycle ergometer tests. Maximal power was measured during this study to obtain information on anaerobic capacity. This fast power in muscles comes from muscle glycogen. During extreme activity intensity, the fuel source is ATP and creatine phosphate (CP); creatine phosphate becomes readily available through the phosphagen system (Whitney). If one were to do a 100-meter sprint, or swing a golf club or baseball bat, these would all be considered extreme activity intensity (Whitney). Extreme activity intensity does not last very long, only five to ten seconds. Very high activity on the other hand, requires ATP from carbohydrates, and not creatine phosphate. Examples of this activity contain a 400 meter sprint or a gymnastics routine; these high activity intensities last anywhere from twenty second to two minutes (Whitney). Overall, these exercises do not require oxygen to be supplied to the muscles, hence the definition of anaerobic-lack of oxygen. (edited by Postlethwaite)

Whitney, Eleanor Noss, and Sharon Rady Rolfes. "MindTap - Cengage Learning." MindTap - Cengage Learning. N.p., n.d. Web. 10 July 2015. <!&parentId=44014278>.

Vandewalle, Henry, Dr, Gilbert Peeres, and Hugues Monod. "Standard Anaerobic Exercise Tests." - Springer. N.p., 01 July 1987. Web. 10 July 2015. <>.

14.2.2 CP-ATP[edit]

During an average day of work done by the body, the majority of force in the muscles is supplied through the Aerobic system, especially through the Krebs Cycle. However, for higher intensity forces applied by the muscles a different kind of structure is used, which is the anaerobic system. This can be broken down into two sub groups, ATP production through Phosphocreatine (PC) breakdown and formation of ATP via Glycolysis. The simplest and fastest way of producing ATP in the body is through the PC system, which forms ATP through the addition of PC to ADP to produce ATP and creatine by the enzyme creatine kinase. (Artiole 2012) During the onset of exercise, on any intensity, ATP is used to create the energy for these force production of the muscles. The muscles then immediately begin the creation of more ATP, starting with the PC system, which is the quickest to respond to the loss and use of ATP by the muscles. However, it is a very short-lived cycle. Due to the fact that there is only a limited supply of Phosphocreatine in the muscles, it can only produce so much ATP before the store runs out. Once the muscles are out of PC they will move on to the next cycles, first starting with Glycolysis. This PC system will be regenerated though, through the reformation of PC during a period of exercise recovery. (Powers & Howley, 2007) In athletics this system is needed for athletes who are competing at events which require a large amount of force production in a very short time span. Events such as a 100 meter dash, high jump, a max out for a weight lifter, and even the sport of diving use almost 100% of the Anaerobic system to supply the ATP needed in the short time period to stress the muscles. (Baker 2010) Their event is done so quickly, the body can’t produce ATP fast enough through the other two systems, so it only uses ATP from the PC system. Because athletes are always looking for a way to be the best, one way to set you apart from the competition is adding more Phosphocreatine to the body in order to have a bigger supply in the muscles, which the PC system can draw from during the onset of exercise. By adding more you allow for a longer use of the PC system, allowing the muscles to be stronger and faster then with a limited supply. Phosphocreatine can be found in a variety of food sources, but the highest amount comes from red meat.

1. Powers, S., & Howley, E. (2007). Exercise physiology: Theory and application to fitness and performance (6th ed.). Boston: McGraw-Hill.

2. Determining the Contribution of the Energy Systems During Exercise (Journal of Visualized Experiments : JoVE) By: Artioli, Guilherme, Rômulo Bertuzzi, Hamilton Roschel, Sandro Mendes, Antonio Jr., and Emerson Franchini.

3. Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise (Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise)

14.2.3 Lactate[edit]

The way in which lactic acid is broken down into energy helps to fuel our bodies to preform the necessary actions in our everyday lives. When we digest glucose, it is digested in our bodies through a process called glycolysis. Glycolysis is the basic metabolic breakdown of glucose to ATP, which provides our muscles energy. When this process is performed in an environment without oxygen, it produces lactate. (Whitney, E., & Rolfes, S., 2013)

There are several specific steps in the chemical process to create lactate. It all starts when glucose is broken down by coenzymes into pyruvate and continues onto the electron transport chain. Since there is an absence of oxygen, the pyruvate will accept the extra hydrogen ions instead of proceeding on through the electron transport chain. Once the pyruvate accepts the hydrogen ions, it then becomes lactate. This process produces small amounts of ATP, but not as much as aerobic respiration creates. (Whitney, E., & Rolfes, S., 2013) Anaerobic respiration is a less efficient way of producing energy, but it is faster then aerobic respiration. (Lactic Acid, 2015)

During intense, prolonged exercise, the muscles in our bodies need lots of energy. However, they become deprived of oxygen and build up with lactate as a result. This lactate cannot be broken down as quickly as it is being produced in our bodies. The small amount of ATP produced during this glycolysis temporarily provides the muscles with enough energy to continue their function until the oxygen levels return to normal. If this rigorous exercise continues, than the build-up of lactate can cause very sharp pains and muscle fatigue. Our muscle cells also become exposed to a low pH because the lactate is acidic. If the lactic acid is not removed from the muscles, than permanent muscle damage can occur. This is why an individual will start to breathe rapidly and heavily while participating in intensive exercise. It is our body’s natural response so it can provide enough oxygen to the muscles so lactate can be converted to aerobic respiration. (Anaerobic Pathways)

Another way in which lactate can be utilized is by circulating it from the muscles to the liver. The liver can transform this lactate back into glucose so that it can be used to refuel your muscles and glycolysis can occur again. This recycling process is called the Cori cycle, named after the scientist who first discovered it. The lactate must be transported to the liver because the muscles cells do not contain the necessary enzyme to initiate this process. (Whitney, E., & Rolfes, S., 2013)


Anaerobic Pathways. (n.d.). Retrieved December 1, 2015, from

Lactic acid. (2015). Retrieved December 1, 2015, from

Whitney, E., & Rolfes, S. (2013). Energy Metabolism. In Understanding Nutrition (14th ed., pp. 206-215). Stamford, Conneticut: Cengage Learning.

14.2.4 Aerobic[edit]

The aerobic energy system consists of aerobic glycolysis, fatty acid oxidation, and the TCA cycle. Muscles in the human body depend on this aerobic system in order to receive ATP for muscle contractions to occur. Aerobic means that oxygen is present. When we consume carbohydrates, fats, and proteins, they are continuously oxidized through glycolysis, fatty acid oxidation, and TCA in order to provide ATP to the body (Whitney). Aerobic energy systems are needed to supply oxygen to the muscles for long-distance efforts such as running, swimming, or cycling. These are all activities that could last anywhere from three to twenty or more minutes (Whitney). Unlike anaerobic exercises, ATP is not immediately available, and there is no creatine phosphate involved. ATP is received from carbohydrates or fats. Aerobic exercise has multiple health benefits. According to a research study on aerobic exercise, “aerobic exercise reduces blood pressure in both hypertensive and normotensive persons. An increase in aerobic activity should be considered an important component of lifestyle modification for prevention and treatment of high blood pressure (Whelton).” That being said, it is important for ones health to incorporate daily exercise for at least twenty minutes to an hour every day.

Whitney, Eleanor Noss, and Sharon Rady Rolfes. "MindTap - Cengage Learning." MindTap - Cengage Learning. N.p., n.d. Web. 10 July 2015. <!&parentId=44014278>.

Whelton, Seamus P., Ashley Chin, MPH, MA, Xue Xin, MD, MS, and Jiang He, MD, PhD. "Effect of Aerobic Exercise on Blood Pressure." Effect of Aerobic Exercise on Blood Pressure. N.p., 2 Apr. 2002. Web. 10 June 2015. <>.