The Muscle System: Key Factors and Nutrition for Regulating Skeletal Muscle Mass

This essay discusses the key factors and nutrition for regulating skeletal muscle mass in the muscle system. It covers the role of anabolic and catabolic pathways, protein synthesis, and nutrient timing. The essay also talks about the importance of consuming sufficient amounts of dietary energy and proteins to maintain skeletal muscle mass. The timing of nutrient intake is also key in regulating skeletal muscle mass. Course code and college/university not mentioned.

The Muscle System1
THE MUSCLE SYSTEM
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The Muscle System2
The Muscle System
Introduction
The muscular system is made up of several tissues all of which are tasked with
performing specific functions. The major muscles of the body consist of the pectoralis major,
rectus abdominis, rectus femoris, gastrocnemius, erector spinae, and bicep femoris among others.
In most cases, when one talks about the muscular system, then the first structures to come to
mind usually are the skeletal muscle tissues. The skeletal muscle tissues are optimized to
contract and move the parts of the body.1 They are generally associated with the parts of the
muscular system which are under the conscious control of humans.
There are three main types of muscles that include the cardiac muscles, smooth muscles,
and the skeletal muscles. The cardiac muscle is solely located in the walls of the heart. The
cardiac muscle is usually under the control of the automatic nervous system. It has a high
number of mitochondria and a good supply of blood that ensures continuous aerobic respiration
and they are therefore resistant to fatigue.1 The smooth muscle, on the other hand, is found in the
walls of organs such as the bronchi, stomach, esophagus, and walls of blood vessels. The skeletal
muscles attach to the bones and mainly functions to facilitate movement through contractions.
According to Gillies and Lieber,2 the primary functions of the skeletal muscle include
movement, support or posture, and the production of heat. The muscles frequently work in
groups to ensure the proper functioning of the body. For muscle contraction to be initiated so that
the muscles can perform their intended tasks, cellular respiration is necessary, and it involves
several metabolic pathways to obtain ATP from the molecules that are rich in energy. In this
essay, we will talk about the key factors the mass of the skeletal muscle in the body. We ill
additionally talk about the role played by nutrition in regulating the mass of skeletal muscle.
Key Factors that Regulate the Mass of the Skeletal Muscle in the Body
The maintenance of the mass of the skeletal muscle strongly depends on the balance
between the rates at which proteins are synthesized and degraded. Different studies in recent
times have revealed that cytokines, hormones, growth factors, nutrients, and mechanical loading
have the capability of activating the signaling pathways which can help in pushing the balance in

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favor of the degradation or synthesis of proteins.3 As a result, the will be a loss or gain in the
mass of skeletal muscle. The two main signaling pathways are anabolic and catabolic pathways.4
Anabolic pathways comprise two factors which are translational capacity and
translational efficiency. Translational efficiency can be described as the synthesis of proteins per
unit amount of Ribonucleic acid. Translational capacity, on the other hand, is described as the
total contents of ribosomes per unit tissue. Most studies have normally focused on the
description of the pathways that enhances translational efficiency.5 As evidenced by several
studies, enhanced translational efficiency takes place over a considerably short frame of time. It
is also normally viewed independently of any variations in the cell’s translational capacity.
Currently, mammalian target of rapamycin (mTOR) is used as the primary hub for the
integration of an array of upstream signaling pathways that result in increased translational
efficiency if activated.4
Catabolic pathways are responsible for the atrophy of skeletal muscle that occurs when
the rate at which protein is degraded is greater than the rate at which it is synthesized. The loss of
the mass skeletal muscles can be witnessed through various factors that may include disuse,
aging, and various diseases such as AIDS, sepsis, diabetes, and cancer among others.6 It is also
important to note that the proteolytic systems that are involved in the in atrophy of the skeletal
muscles respond to several triggers including disuse, hormones, growth factors, oxidative stress,
and inflammatory cytokines among others.
It has also been revealed by several studies that factors such as fatty acids which are
nutrient modulated may act differently to regulate the mass of the skeletal muscle. This can be
shown by exposing C2C12 myotubes to palmitate. Palmitate is the most abundant saturated fatty
acid that is in circulation. This exposure reduces the diameter of the myotube thus suppressing
insulin signaling.6 The impairment of the signaling may lead to the loss of muscle mass.
The Role of Nutrition in Regulating the Mass of Skeletal Muscle
Nutrition plays an essential role in the regulation of the skeletal muscle mass. The
maintenance of the mass of the skeletal muscle is described by a perfect balance between protein
degradation and protein synthesis.7 There is an increase in skeletal muscle if a gain exists during
protein synthesis. This gain occurs typically during regular exercises. A loss of the skeletal

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muscle, on the other hand, occurs when degradation of proteins is more rapid than synthesis.7-8
We will, therefore, focus on the type of nutrients that should be ingested to aid in regulating
skeletal, muscle mass, the amount to be ingested, the timing of the ingestion of the nutrients, any
other nutritional considerations, and the potential limitations.
Some of the nutritional determinants of skeletal muscle mass are dietary energy and
intake of proteins. According to several studies, it is essential to consume sufficient amounts of
dietary energy and proteins to maintain the skeletal muscle mass. The activation of muscle
protein synthesis is determined by the quantity of dietary protein that an individual consumes.6 It
is worth noting that taking diets that are high in protein content helps in attenuating decrements
in the muscle protein synthesis. As a result, the skeletal muscle mass is controlled during a
deficit of energy. Researchers have ascertained that controlling the mass of skeletal muscles is
very crucial in ensuring that one lives a healthy life throughout their lifespan. Ingesting a dietary
protein that is way above the recommended dietary allowance in moments of energy balance
enhances the retention of nitrogen which may, in turn, up-regulate muscle protein synthesis.9
This results in the promotion of a favorable balance of protein and accretion of skeletal muscle.
Amounts of Nutrients Ingested
The consumption of high protein diets that range between 1.6-2.4 g/kg on a daily basis or
meals based on protein during energy deficit periods is reported to attenuate intracellular
proteolysis. Additionally, it restores the synthesis of muscle protein and mitigates the loss of
skeletal muscle mass. The United States recommended dietary allowance suggests that an
individual should consume 0.8g/kg of protein daily to maintain the skeletal muscle mass.10 It is,
however, worth noting that the protein requirements increase above the recommended dietary
allowance during increased energy demands. These requirements increase to sustain the retention
of protein and maintain the mass of the skeletal muscle.11 The recommendations also suggest that
the physically active individuals such as athletes and those who take part in aerobics should
consume 1.2-1.7 g protein/kg on a daily basis. The military personnel, on the other hand, need to
consume a diet that provides around 1.5-2.0 g/kg of protein every day. This group of people is
none to take part in combat operations and very challenging metabolic training and thus needs
this amount of protein daily to aid in the repair the damaged protein and the synthesis of new

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muscle proteins thus maintaining the skeletal muscle mass.12 This is one of the reasons why high
protein diets are gaining new popularity among the physically active individuals.
As had been previously stated, the quantity of dietary protein ingested determines the
activation of muscle protein synthesis.6 Studies reveal an existing dose-dependent relationship
between dietary protein and muscle protein synthesis. Therefore, consuming a meal that contains
around 0.25-0.30 g/kg maximally stimulates postprandial muscle protein synthesis for around 2
hours.12 Consuming high doses of proteins leads to an increase in the oxidation of proteins with
no additional anabolic stimulus.
Nutrient Timing
The timing of nutrients intake is a very important factor in muscle hypertrophy. A person
who exercises frequently needs to practice nutrient timing to ensure that they can appropriately
regulate their skeletal muscle mass. Studies reveal that timing of the nutrients ingestion can shift
hormonal profile, up-regulate metabolism, or alter the composition of the body.13 The
manipulation of nutrient intake also helps an individual to take advantage of some anabolic
hormones like insulin. It is important to note that nutrient timing helps the body to prioritize in
muscle gain rather than fat gain.13
Pieces of evidence on the timing of milk consumption reveal that consuming milk
moments after work-outs is essential in enhancing muscle hypertrophy. Milk proteins are very
fundamental in the development of skeletal muscles.14 The timing of essential amino acids is also
crucial in protein synthesis that helps in the regulation of skeletal muscle mass. Studies indicate
that, consuming essential amino acids moments before a resistance exercise enhances protein
synthesis. It is therefore important to have an appropriate personal schedule that helps in
reminding one about the appropriate time of the consumption of nutrients.14 Such a schedule
helps in ensuring effective absorption of the nutrients by the skeletal muscles.
Other Nutritional Consideration
It is important to maintain energy balance in the body to regulate the skeletal muscle
mass. Ingesting inadequate energy is known to accelerate the loss of muscles during disuse
massively. Additionally, excess energy results in the deposition of fats that may lead to
unnecessary weight gain.15 Other nutritional considerations that can be used to regulate the

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skeletal muscle mass includes the ingestion of carbohydrates. Special attention is given to
glucose which is widely reported to be a precursor for glycogen re-synthesis. Ingestion of
carbohydrates increases the storage of glycogen above that of water. Reports also reveal that
ingesting 6 to 12 g carbohydrates/ kg daily, is enough to restore the glycogen reserves provided
that the recovery time is more significant than 24 hours.
It is widely known that glucose significantly stimulates the pancreas to release insulin.
However, protein ingestion by healthy individuals also stimulates insulin secretion. An evidence-
based research report that the level of muscle glycogen re-synthesis rises when there is a protein
co-ingestion with carbohydrates.15 This co-ingestion will have positive effects on the regulation
of skeletal muscle mass.
Potential Limitations
The proposals and recommendations as mentioned above, however, have some
limitations, especially in injured individuals. Managing the balance between the conservation of
skeletal muscle mass and the prevention of body fat accrual in injured athletes are some of the
main challenges faced by general practitioners.16 Injuries lead to a reduction in physical activities
and the general energy requirements which interferes with the regulation of skeletal muscle
mass. This is because, during injuries, the athlete experiences disuse and thus inadequate intake
of dietary energy may lead to the loss of skeletal muscle mass. However, the consumption of
excess energy also leads to aft deposition that may lead to weight gain. These recommendations,
therefore, pose a challenge to the injured athletes due to the difficulty of balancing between the
conservation of muscle mass and fat accrual.
Conclusion
The skeletal muscles have tissues that are optimized to contract and enhance the
movement of the body parts. Its main functions include movement, support, and heat production.
The maintenance of the mass of the skeletal muscle strongly depends on the balance between the
rates at which proteins are synthesized and degraded. Some of the nutritional determinants of
skeletal muscle mass are dietary energy and intake of proteins. It is essential to consume
sufficient amounts of dietary energy and proteins to maintain the skeletal muscle mass. It is

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important to note that the quantity of dietary protein ingested determines the activation of muscle
protein synthesis. The timing of nutrients intake is key in regulating the skeletal muscle mass.

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