Energy systems The skeletal muscle has three types

Energy systems The skeletal muscle has three types

Energy systems

Energy systems The skeletal muscle has three types of energy sources whose use varies according to the physical activity performed. These are:

 

Alactic anaerobic system or phosphagen system: Conversion of high energy reserves from the form of phosphocreatine (PC) and ATP

The lactic anaerobic system, anaerobic glycolysis or glycogen-lactate system: Generation of ATP by anaerobic glycolysis

Aerobic system or oxidative system: Oxidative metabolism of acetyl-CoA

ATP

Graph 1. Food degradation

The energy systems operate as an energy continuum (Figure 1). This can be defined as the ability of the body to simultaneously keep the three energy systems active at all times, but giving predominance to one of them over the rest according to:

 

Duration of exercise.
The intensity of muscle contraction.
Amount of substrates stored.

Thus, in power activities (a few seconds long and of high intensity) the muscle will use the so-called phosphagen system (ATP and phosphocreatine); For activities lasting around 60 seconds at the maximum intensity possible, you will preferably use non-oxidative glycolytic energy sources ( anaerobic metabolism ), while for activities lasting more than 120 seconds, the aerobic system ( aerobic metabolism ) will be the one that supports mainly energy demands.

 

 

 

2. Alactic anaerobic system or phosphagen system:

This system provides the energy necessary for muscle contraction at the beginning of exercise and during very high intensity and short duration exercises (see table 1). It is limited by the intramuscular reserves of ATP (adenosine triphosphate) and PCR (phosphocreatine), which are compounds that are directly used for obtaining energy.

 

It is called galactic because it has no accumulation of lactic acid. Lactic acid is a metabolic waste that produces muscle fatigue.

 

The amount of ATP stored in the muscle cell is so small that it only allows work to be done for a very few seconds. Therefore ATP must be constantly recycled in cells; Some of the energy required for ATP resynthesis in the muscle cell occurs rapidly and without the involvement of oxygen through the transfer of chemical energy from another high-energy phosphate-rich component, phosphocreatine (PC).

 

The Phosphagen system works by breaking an ATP bond. This link can store up to 7300 calories; These are released in two stages, when ATP is subdivided twice, first into ADP (adenosine diphosphate) and finally into AMP (adenosine monophosphate).

 

Creatine phosphate has a high-energy phosphate bond, about 10,300 calories per mole, which allows it to supply energy for the reconstitution of ATP and thus allow a longer period of maximum force utilization of up to ten seconds in duration, enough to perform short series of movements at maximum speed and power, also applicable to a series of basic exercises. In this way, we conclude that the Phosphagen System is used for short muscle efforts and of maximum demand.

 

3. Lactic anaerobic system or anaerobic glycolysis:

It participates as a fundamental energy source in sub-maximum intensity exercises (between 80 and 90% of the MIC or individual maximum capacity) and lasts between 30 seconds and 1 or 2 minutes. This metabolic pathway provides maximum energy after 20-35 seconds of high-intensity exercise and decreases your metabolic rate progressively as the oxidative rate increases around 45-90 seconds.

 

The anaerobic lactic system is limited by intramuscular glycogen stores as an energy substrate. This means that the chemical fuel for ATP production is glycogen stored in the muscle.

 

This energy system produces less energy per unit of a substrate (less ATP) than the aerobic route and as a final metabolic product lactic acid is formed that causes an acidosis that limits the ability to exercise, producing fatigue. Lactic acid or lactate, is the result of intense muscular combustion, in the absence of oxygen (anaerobic), it is acidic, therefore it causes metabolic acidosis and therefore inhibition of the biochemical machinery responsible for the production of energy from the breakdown of blood glucose and muscle glycogen.

 

Depending on the duration of the effort carried out, two types of anaerobic systems are distinguished.

Table 1: Characteristics of anaerobic systems

Alactic anaerobic system Lactic anaerobic system

It works without receiving oxygen or in a negligible quantity Does not produce lactic acid

Works without receiving oxygen Lactic acid is produced, causing fatigue and decreasing cellular function

Uses the muscle's energy It is produced by the breakdown (lysis) of muscle glycogen (glucose) or glucose from the liver, into lactic acid (glycolysis)

The duration of the high-intensity effort is 0 to 15 - 20 seconds The duration of the high-intensity effort ranges from 15 - 20 seconds to 2 minutes

Two ways appear:

ATP (lasts 2 - 3 seconds) ATP → ADP + P + Energy

ATP + CP (lasts from 2 to 15-20 seconds) ADP + CP → ATP + C

Via:

ATP + O2 deficiency → lactic acid

The glycogen stored in the muscle, after the ingestion of carbohydrates and at times of low muscle activity, can be degraded, when necessary, by the action of glycogen phosphorylase into phosphorylated glucose, which is used for energy.

 

The initial stages of the glucose breakdown process, glycolysis, occur without the use of oxygen, constituting what is known as anaerobic glycolysis. During this glycolysis, each glucose molecule is converted into two pyruvic acid molecules and two net ATP molecules are produced.

 

Normally, pyruvic acid enters the mitochondria of muscle cells and, when oxidized, forms a large amount of ATP. However, when the supply of oxygen is insufficient for this second oxidative stage of glucose metabolism to take place, most of the pyruvic acid is converted to lactic acid, which diffuses out of the muscle cells and reaches the blood. For this reason, much of the muscle glycogen, in these circumstances, is converted into lactic acid but, in doing so, certain amounts of ATP are formed, even without oxygen.

 

This glycogen-lactic acid system can form ATP molecules 2.5 times faster than the oxidative mechanism of the mitochondria. When large amounts of ATP are required for a moderate period of muscle contraction, this anaerobic glycolysis mechanism can be used as a rapid source of energy production.

 
4. Aerobic or oxidative system:

When an individual makes an effort at a constant rate (for example, running, walking, pedaling, or swimming at a uniform intensity) and this effort lasts for a few or many tens of minutes, the energy used by his muscles derives all from the combination of oxygen with sugars or also with fats.

Precisely the energy production mechanism that is based on these combinations, oxygen plus sugars, or also oxygen plus fats, is called "aerobic".

 

Oxygen is the vital ingredient that allows food to be transformed into a source of energy used by the muscle and it is impossible without its use to develop physical exercise for long periods.

 

The aerobic system participates as an energy source predominantly around 2 minutes of exercise, being the most profitable energy route and with end products that do not cause fatigue. It is the most important metabolic pathway in long-term exercises.

 

Its limitation can be found at any level of the oxygen transport system from the atmosphere to its use at the peripheral level in the mitochondria. Another important limitation is that which refers to energy substrates, that is, to the storage and utilization capacity of muscle and liver glycogen, and to the ability to metabolize fats and ultimately proteins.

 

5. Summary of particularities of energy systems:

Table 2. Summary of energy systems

7. Bibliography:

"Everest Family Encyclopedia of Health"; various authors; Edit. Everest, León (Spain) 2000.

"Invitation to biology"; Helena Curtis, N Sue Barnes; Edit. Pan American; Madrid, 1994.

"Encyclopedia of the human body"; various authors; Edit. Espasa Calpe; Spain 2003.

"Physiology of exercise": J. López Chicharro, A. Fernández Vaquero; Edit. Pan American; Madrid 2001.

"Neuroanatomy Online Course". Dept. of Anatomy, School of Medicine Pontificia Universidad Católica de Chile.