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How the Skeletal Muscles Derive the Energy for Contraction Essay

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Updated: Apr 7th, 2022


The muscular system refers to the human biological system that makes movement possible. In vertebrates, the nervous system controls the muscular system. However, muscles such as the cardiac muscles are entirely autonomous. The term muscle refers to a contractile tissue that develops from the embryonic germ cells’ mesodermal layer. The muscle’s role is to make movement possible and produce force.

In this regard, motion refers to either movement in the internal organs or locomotion. A majority of the muscle contraction occurs in the absence of conscious thought. Moreover, muscle contraction is necessary for survival. For instance, peristalsis allows food to move in the digestive system (Fitzgerald, 1996). Body movement uses voluntary muscle contraction, which can be manipulated finely. This includes the finger or triceps movement.

Muscles are made up of muscle fibres or cells. The skeletal muscles possess a detached organization as seen in the biceps brachii. Tendons connect the skeletal muscles. In a human body, there are approximately six hundred and forty skeletal muscles. The body has three different kinds of muscles; skeletal, cardiac, and smooth muscles. Irrespective of the fact that the three kinds of muscles are different in many aspects, all of them utilize myosin and actin to allow relaxation and contraction.

In the skeletal muscles, nervous impulses that are present in every cell permit contraction. Acetylcholine is released at the neuromuscular junction, which brings about action potentials in the cell membrane. Acetylcholine is a vital neurotransmitter during muscle contraction. Its binding stimulates the contraction of skeletal muscles. A majority of the energy consumption in the body is as a result of muscular activity (Goldstein, 2010). In the muscles, energy is stored in the form of glycogen, which can be transformed into glucose when more energy is obligatory. This paper aims at discussing how the skeletal muscles acquire the energy for contracting.

When muscles are contracting, ATP is useful as an instantaneous energy source. Irrespective of the fact that the skeletal muscle fiber has only sufficient ATP to enable several twitches, the ATP store is usually restocked as required. A phosphate with high levels of energy can be derived from three sources. This ensures that the ATP store is sufficient. It is worth pointing out that cellular respiration takes place in the fibres’ mitochondria.

Creatine Phosphate

Creatine phosphate possesses a phosphate group that is attached using a bond with a lot of energy. This bond is similar to that found in ATP. Creatine phosphate acquires the phosphate that has immense energy from ATP. This can be demonstrated in the following equation:

Creatine phosphate + ADP = ATP + Creatine.

It is worth pointing out that the fiber has a creatine phosphate pool that is approximately ten times bigger compared to that found in ATP. Therefore, creatine phosphate is regarded as a modest ATP pool.


The skeletal muscle fibres possess approximately one percent of glycogen. Moreover, the muscle fiber has the ability to breaking down the glycogen through a process referred to as glycogenolysis. The process leads to the formation of glucose- 1- phosphate, which gets into the glycolytic pathway. ATP molecules can be produced from lactic acid particles. The ATP that is produced is adequate for the functioning of muscles. This is in cases where there is insufficient oxygen supply to cater for the respiration. It is worth pointing out that glycogen, as a source of energy, is extremely limited. Therefore, the muscles have to rely on cellular respiration.

Cellular Respiration

Cellular respiration plays various roles in the body. First, cellular respiration is necessary to satisfy ATP requirements during instances when the muscles are involved in prolonged activity. This results to deeper and rapid breathing. In addition, cellular respiration allows resynthesizes of glycogen from the previously formed lactic acid. As far as cellular respiration is concerned, it is worth noting that deep and rapid breathing goes on after the exercise is terminated. This implies that the body has to repay the oxygen debt.

Muscle contraction

There are several processes involved during muscle contraction. It is worth noting that muscle contraction requires huge ATP energy supplies. The energy used during muscle contraction is derived from ATP. ATP molecules are derived from fatty acids and glucose metabolism. It is imperative to note that minimal amounts of ATP are kept in the muscles. This implies that several twitches have the ability of exhausting the supplies within minutes.

Obviously, the muscles have to possess alternative ways of curbing the limitation (Goldstein, 2010). Minimal amounts of ATP are usually stored in the skeletal muscles. In addition, creatine phosphate is kept in the muscles. Creatine phosphate is formed from a combination of creatine and phosphate group. It does not provide direct energy required for muscle contraction. However, creatine phosphate can donate the phosphate group to the ADP, which results to ATP.

The resultant ATP is used as a direct energy source during muscle contraction. There are sufficient creatine phosphate stores in the muscles, which allows for strong contractions. Later, cellular respiration and glycolysis are used to provide additional energy. The oxidation of fatty acids and glucose provides energy to the muscles when more energy is necessary.

This produces water and carbon dioxide. The process uses oxygen. Some of the oxygen required during aerobic respiration in the red muscles is generated from oxygenated myoglobin. Myoglobin refers to a protein that is located in the muscles and used for storing oxygen. Similar to haemoglobin, myoglobin forms a loose link with oxygen. This occurs when there is plenty oxygen supplies. The combination is held until oxygen demands escalate. Eventually, the muscles have an internal supply for oxygen.

In situations where the skeletal muscles are involved in laborious muscular activity, for instance when lifting heavy objects or during intensive exercise, there are huge energy demands (Purves, Augustine & Fitzpatrick et al, 2004). During such cases, the oxygen attached to myoglobin is utilized quickly. Considering that it is impossible to get adequate oxygen into the tissues as quickly as possible, the muscles acquire additional energy from anaerobic procedures. This calls for lactic acid production, which is accomplished via fermentation.

This results to oxygen debt. A small amount of the lactic acid collects in the muscles. However, the rest gets into the muscle capillaries and is taken to the liver. The blood acts as the medium through which lactic acid is carried. After a person engages in laborious exercise, he experiences a period of panting and hard breathing, which is useful for supplying the liver with adequate amounts of oxygen. This oxygen is vital for aerobic respiration and assists in covering for the oxygen debt. While in the liver, pyruvic acid is formed from lactic acid. Oxidation of pyruvic acid forms water and carbon dioxide. Moreover, ATP energy uses the extra lactic acid to manufacture glycogen and glucose.

It is worth pointing out that lactic acid should be removed from the muscle fibres straightaway. Otherwise, extreme damages can be experienced. In this regard, a resting period is extremely important after a person experiences strenuous exercise. There is need for an uninterrupted blood flow in the muscles, which is useful for getting rid of lactic acid. Lactic acid should never be allowed to accrue in the muscles. This prevents sore muscles and guards the muscle proteins.

In this regard, endurance- training strategies designed for athletes aim at ensuring that more oxygen is available to the muscles. This measure promotes aerobic metabolism. During instances of endurance- training programs, there is an increase of mitochondria in the muscle fibres. In addition, there is an increase in myoglobin and novel blood capillaries. Consequently, blood circulation increases in the muscles. Athletes who have been trained have greater capabilities for undergoing through laborious exercise because there is increased accumulation and manufacture of lactic acid.

Usually, a spasm or cramp comes with abrupt pain. The pain is as a result of the pain receptor stimulators, which functions mechanically in the muscle (Fitzgerald, 1996). Furthermore, the pain may be as a result of compression to the blood vessels, which interrupts with oxygen delivery to the muscle fibres. It is worth noting that a majority of the muscle cramps is as a result of calcium deficiency, which is more common in pregnant women. Calcium is not only used for forming calcium phosphate, which composes dentin, enamel, and hardened bone. Calcium plays a vital role during muscle contraction.

Skeletal muscles derive ATP through anaerobic and aerobic respiration. In addition, energy can be derived from the phosphate groups present in creatine phosphate. It is worth emphasizing that anaerobic and aerobic capacity in skeletal muscle fibres vary depending on the type of muscle fiber. Moreover, muscle fibres are differentiated based on the colour, contraction speed, and key energy metabolism modes (Kandel, Schwartz & Jessel, 2000).

During rest, skeletal muscles acquire energy from fatty acids’ aerobic respiration. When the muscles are undergoing through strenuous exercise, glucose in the blood and glycogen stored in the muscles are used for providing energy. Cell respiration provides energy that is essential for making ATP. This energy source is essential since it is instant. The energy is used for moving cross bridges when muscles are contracting and pumping calcium during muscle relaxation. During the initial forty five to ninety seconds of moderate to laborious exercise, skeletal muscles experience anaerobic respiration. This is attributed to the fact that the cardiopulmonary system needs approximately this period to ensure adequate oxygen uptake by the exercising muscles. During moderate exercise, aerobic respiration supplies most of the energy to skeletal muscles.

Irrespective of the fact that a person is engaging in strenuous, moderate, or light exercise, the person’s maximum ability for aerobic exercise is extremely important. Aerobic capacity refers to the greatest rate at which energy is taken up in the body. Aerobic capacity is dependent on a person’s sex, size, and age.

According to Martini and Nath (2009), solid and prolonged muscle contractions results to a state referred to as muscle fatigue. During cases of moderate exercise, fatigue is experienced after the muscle fibres use all the glycogen stores. During such moments, there is inadequate supply of oxygen. Consequently, muscle fibres use anaerobic respiration and pyruvic acid is turned into lactic acid. On the contrary, there is no aerobic metabolism in the mitochondrion. This is extremely vital since excessive accumulation of lactic acid results to extreme fatigue.

Lactic acid production in the skeletal muscle fibres results to increased hydrogen ions and reduced PH. A reduction of PH in the muscles hinders the performance of principal glycolytic enzymes, which reduces the level of ATP production. ATP is necessary for the active transportation of calcium. Therefore, a reduction in ATP results to loss of calcium, which consequently interferes with excitation- coupling in skeletal muscle fibres. During fatigue, there is accumulation of lactic acid that results from minimised supplies of ATP. This results to decelerated muscle excitation.

It is important that athletes understand the mechanisms involved in skeletal muscles. This ensures that their muscles remain strong and do not suffer from cramps, which may interfere with their performance. Prolonged training sessions assist in building strong muscles. In order to ensure adequate energy stores in the body, there is a need to consume energy rich foods. Exercise should be done frequently to ensure solid muscles. There are many benefits associated with exercise; improved motor skills, bone and muscle strength, fitness, and prevention of muscle diseases. A person can engage in anaerobic or aerobic respiration. Therefore, it is recommendable for athletes to engage in regular strenuous exercise.


Fitzgerald, MT 1996, Neuroanatomy Basic and Clinical, Saunders, London.

Goldstein, EB 2010, Sensation and Perception, Wadsworth Cengage Learning, London.

Kandel, ER, Schwartz, JH & Jessel, TM 2000, Principles of Neural Science, McGraw Hill, New York.

Martini, FH & Nath, JL 2009, Fundamentals of Anatomy & Physiology, Pearson, New York.

Purves, D, Augustine, GJ, Fitzpatrick D et al 2004, Neuroscience, Sinauer Associates, Sunderland (USA).

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