Why Do Heart Muscle Cells Have Lots Of Mitochondria?

Why Do Heart Muscle Cells Have Lots Of Mitochondria
The heart muscle has a large number of mitochondria to provide sufficient energy. The heart muscle needs the energy to pump blood into the body. Pumping is promoted by mitochondria.

Why does heart muscle contain more mitochondria than skeletal muscle?

Brent Cornell

Understanding: • Structure of cardiac muscle cells allows propagation of stimuli through the heart wall

The heart is composed of cardiac muscle cells which have specialised features that relates to their function:

Cardiac muscle cells contract without stimulation by the central nervous system (contraction is myogenic ) Cardiac muscle cells are branched, allowing for faster signal propagation and contraction in three dimensions Cardiac muscles cells are not fused together, but are connected by gap junctions at intercalated discs Cardiac muscle cells have more mitochondria, as they are more reliant on aerobic respiration than skeletal muscle

These structural features contribute to the unique functional properties of the cardiac tissue:

Cardiac muscle has a longer period of contraction and refraction, which is needed to maintain a viable heart beat The heart tissue does not become fatigued (unlike skeletal muscle), allowing for continuous, life long contractions The interconnected network of cells is separated between atria and ventricles, allowing them to contract separately

Structure of Cardiac Muscle Cells : Brent Cornell

Why do muscles the heart and the brain have more mitochondria than other cells of the body?

Snapshot: What are mitochondria? Every organ in our body requires a constant supply of energy to function. Our brain and muscles, for instance, need energy to perform tasks such as thinking, walking, and running. The major energy generators in our cells are compartmentalized machines known as “mitochondria.” Mitochondria rely on a series of biochemical steps (collectively referred to as “cellular respiration”) to create ATP (adenosine triphosphate), which is used throughout the cell as a common currency for energy-dependent processes.

  1. Almost all cellular processes require ATP, making it a critical part of cellular health and survival.
  2. When we eat, our food gets broken down into nutrients such as proteins, fats, and sugars.
  3. In the mitochondria, these nutrients are processed further to generate molecules of ATP.
  4. You may have heard mitochondria referred to “the powerhouses of the cell” for their role in producing ATP – because the cell uses energy nearly exclusively in the form of ATP, mitochondria are the major fuel source for our bodies.

Some cells, like brain and muscle cells, require much more energy, and therefore contain many more mitochondria than cells that are less active. Additionally, the need for mitochondria can change in different parts of the body depending on energy demands. Cartoon of mitochondria with its different features labeled. Image courtesy of Wikimedia. Mitochondria are classically represented as oval-shaped, but that’s not always the case: they can have a shape anywhere from a long tube to a small sphere. Mitochondrial contents are held in by two separate layers or “membranes”.

  • The inner membrane is dotted with several proteins that perform complex chemical reactions (known collectively as “oxidative phosphorylation”) to turn the broken-down nutrients of our food into ATP.
  • An important feature of the inner membrane is that it folds into “cristae.” These cristae allow more membrane to be packed into less space.

With a larger surface area, more reactions can occur simultaneously, thus increasing the efficiency of ATP production.

Do cardiac muscle cells have mitochondria?

Abstract – In cardiac muscle cells, mitochondria occupy about 40% of the total volume (Page and McCallister, 1973) and provide about 90% of the ATP required under normal aerobic conditions (Neely and Morgan, 1974). In addition to being the major source of ATP, mitochondria contain distinct Ca 2+ influx and efflux systems (Carafoli, 1979), the role of which in cell function is still incompletely understood.

The structure and function of mitochondria are known to be damaged in such disease conditions as myocardial ischemia (Jennings and Ganote, 1974; Rouslin, 1983; Rouslin and Millard, 1980, 1981; Sordahl and Stewart, 1980; Wood et al,, 1979; Nagao et al,, 1980) and heart failure (Lindenmayer et al,, 1968, 1970, 1971; Lochner et al,, 1968; Meerson et al,, 1964; Rouslin et al,, 1979; Schwartz and Lee, 1962; Wollenberger et al,, 1963).

A major thrust of research in this area has been the elucidation of mechanisms and factors responsible for mitochondrial damage and the design of pharmacological interventions to prevent cellular injury. In most of these studies, it is necessary to study the structure and function of mitochondria in vitro after isolation and purification.

Why liver or heart cells have more mitochondria in comparison to skin cells?

The heart cell has many mitochondria as it is required to contact repeatedly for the whole life of the person without ever stopping whereas the skin cells have fewer mitochondria as cell division requires less energy than muscle contraction and skin cells do not need to divide all the time.

How much mitochondria is in a heart muscle cell?

eLife digest – A small molecule called ATP is often referred to as the primary “energy currency” of living cells. It is required to power tasks as diverse as the general housekeeping processes that keep all cells alive to the programmed cell death response that dismantles any cells that are no longer needed.

  1. It is also crucial that cells maintain a constant level of ATP at all times, even when the supply of and demand for ATP fluctuate.
  2. This control is particularly important in the mammalian heart where the rates of ATP production and consumption change ten-fold during intense exercise.
  3. Despite intensive research over the past decades, it was still not known how cells keep ATP levels constant.

In many cell types, including heart muscle cells, ATP is mainly produced inside compartments called mitochondria. Each heart muscle cell contains between 5,000 and 8,000 mitochondria. Recent experiments have shown that ATP production in mitochondria is interrupted by ten-second bursts called “mitochondrial flashes” (or mitoflashes for short), during which the mitochondria release chemicals called reactive oxygen species.

  • The mitoflashes are tightly linked with energy usage, and Wang, Zhang, Wu et al.
  • Have now explored if and how mitoflashes regulate ATP levels in the heart.
  • Experiments on isolated mitochondria from mouse heart muscle cells showed that mitoflashes inhibit the production of ATP.
  • When the intact heart muscle cells were given excess of the building blocks needed to produce ATP – mitoflashes occurred more often.

Conversely, when the cells were forced to contract more quickly, which increased demand for ATP, the mitoflashes occurred less often. Importantly, the level of ATP inside the cells actually remained constant in the experiments. Furthermore, inhibiting mitoflashes with antioxidants increased the ATP concentration in heart muscle cells.

  • Lastly, Wang et al.
  • Demonstrated that mitoflashes could be triggered under certain conditions.
  • Overall, these experiments uncovered a way in which highly active cells can maintain a constant level of ATP.
  • Future studies are needed to understand exactly how mitoflashes are initiated and how they in turn inhibit ATP production.

A better understanding of these processes might uncover molecules that could be targeted by drugs to the control of the rate of ATP production to treat heart failure. https://doi.org/10.7554/eLife.23908.002

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Do heart cells have high concentration of mitochondria?

Abstract – Unlike cardiac and skeletal muscle, little is known about vascular smooth muscle mitochondrial respiration. Therefore, the present study examined mitochondrial respiratory rates in smooth muscle of healthy human feed arteries and compared with that of healthy cardiac and skeletal muscles. Cardiac, skeletal, and smooth muscles were harvested from a total of 22 subjects (53 ± 6 yr), and mitochondrial respiration was assessed in permeabilized fibers. Complex I + II, state 3 respiration, an index of oxidative phosphorylation capacity, fell progressively from cardiac to skeletal to smooth muscles (54 ± 1, 39 ± 4, and 15 ± 1 pmol·s −1 ·mg −1, P < 0.05, respectively). Citrate synthase (CS) activity, an index of mitochondrial density, also fell progressively from cardiac to skeletal to smooth muscles (222 ± 13, 115 ± 2, and 48 ± 2 μmol·g −1 ·min −1, P < 0.05, respectively). Thus, when respiration rates were normalized by CS (respiration per mitochondrial content), oxidative phosphorylation capacity was no longer different between the three muscle types. Interestingly, complex I state 2 normalized for CS activity, an index of nonphosphorylating respiration per mitochondrial content, increased progressively from cardiac to skeletal to smooth muscles, such that the respiratory control ratio, state 3/state 2 respiration, fell progressively from cardiac to skeletal to smooth muscles (5.3 ± 0.7, 3.2 ± 0.4, and 1.6 ± 0.3 pmol·s −1 ·mg −1, P < 0.05, respectively). Thus, although oxidative phosphorylation capacity per mitochondrial content in cardiac, skeletal, and smooth muscles suggest all mitochondria are created equal, the contrasting respiratory control ratio and nonphosphorylating respiration highlight the existence of intrinsic functional differences between these muscle mitochondria. This likely influences the efficiency of oxidative phosphorylation and could potentially alter ROS production. Keywords: oxidative phosphorylation capacity, respiratory control ratio, feed arteries the integrated function of cardiac, skeletal, and vascular smooth muscles is essential for O 2 delivery and utilization, especially during exercise, when synchronicity can determine capacity. Cardiac muscle produces the driving force to convectively transport blood-borne O 2 to the periphery, where skeletal muscle uses this O 2 for the metabolic requirements of locomotion ( 35, 36 ). Smooth muscle, the major component of the arterial system, dictates the distribution of blood flow and O 2 transport, dependent on need ( 6, 33 ). Each of these distinct muscle tissues contain mitochondria, which consume O 2 and produce ATP through cellular respiration. Interestingly, although mitochondrial respiration of both cardiac and skeletal muscles has been studied extensively in health and disease ( 4, 5, 31, 32, 39 ), little is known about smooth muscle mitochondrial respiration ( 42 ). The heart is a vital organ with a high metabolic demand and is subsequently rich in mitochondria, with these mitochondria accounting for ∼35% of the volume of cardiac tissue ( 39 ) and generating up to 90% of ATP requirements by β-oxidation at rest ( 21, 28, 30 ). Attenuated coupled respiration and an increase in uncoupled respiration in cardiac muscle are common indicators of heart disease ( 4 ). Indeed, diseased hearts often exhibit decreased oxidative phosphorylation, secondary to both reduced mitochondrial enzymes and content ( 27, 47 ), and excessive mitochondrial free radical production in human and animal models ( 16, 38 ). In skeletal muscle, due to the high metabolic requirements for locomotion, mitochondrial ATP production is also certainly important, with typically 3–8% of the skeletal muscle volume being mitochondria ( 23 ), but this is highly dependent on physical activity. Additionally, studies have revealed that a reduction in skeletal muscle mitochondrial oxidative phosphorylation capacity and/or volume may contribute to muscle dysfunction ( 11 – 13 ). Therefore, understanding and characterizing mitochondrial function in both cardiac and skeletal muscles has implications in both health and disease. Although far less well studied, the mitochondria within smooth muscle are thought to play a role in maintaining vascular tone, facilitating cellular transport, and producing energy for vascular cell secretion ( 42, 46 ). These mitochondria typically comprise 3∼5% of the smooth muscle cell volume ( 3 ). Until recently, little was known about the role of vascular smooth muscle mitochondria in terms of vascular function and disease. Now, new evidence suggests the potential importance of mitochondrial function in the development of vascular diseases ( 14, 43, 45 ). However, it is important to note that most of these studies used mitochondrial protein expression or protein activity to estimate mitochondrial function rather than actual measurements of mitochondrial respiratory capacity, and, hence, direct assessments of mitochondrial respiration in vascular smooth muscle are still lacking. Indeed, there has yet to be a comprehensive assessment of mitochondrial respiratory rate in smooth muscle and a comparison of this function with cardiac and skeletal muscles. Recognizing the lack of data specific to mitochondrial function in smooth muscle of the vasculature, the present study sought to assess mitochondrial respiration in smooth muscle of skeletal muscle feed arteries and compare this with that of cardiac and skeletal muscles. Due to the anticipated differences in mitochondrial density between cardiac, skeletal, and smooth muscles, in conjunction with the vastly different functional requirements of each, it was hypothesized that, on a mitochondrion-to-mitochondrion basis, respiratory function would be very similar. This would indicate that all muscle mitochondria are created equal in terms of respiration, regardless of origin.

What does mitochondria have to do with the heart?

1. Introduction – Mitochondria play critical roles in both the life and death of cardiac myocytes. In healthy cells, their primary function is to meet the high energy demand of the beating heart by providing ATP through oxidative phosphorylation. Mitochondria occupy a large portion of each myocyte and are located between the myofibrils and just below the sarcolemma.

The strategic positioning and abundance of mitochondria ensure a highly efficient localized ATP delivery system to support contraction, metabolism, and ion homeostasis.1 However, mitochondria are also important regulators of cell death, responding to a wide variety of stress signals, including loss of growth factors, hypoxia, oxidative stress, and DNA damage.

The switch to a cell death program can be mediated by opening of the mitochondrial permeability transition pore (mPTP) in the inner mitochondrial membrane, causing collapse of the membrane potential and swelling of the mitochondria, 2 often culminating in necrotic cell death, or permeabilization of the mitochondrial outer membrane (MOM) with release of proapoptotic proteins such as cytochrome c, Smac/Diablo, and apoptosis-inducing factor (AIF) to activate an energy-dependent apoptosis.3 It is important to remember that both forms of cell death are highly regulated and activated by mitochondria.

  1. During apoptosis, the cell activates a signalling cascade which leads to cell death without triggering an inflammatory response.
  2. In contrast, necrosis is characterized by swelling of the cell and disruption of the plasma membrane.
  3. The resulting release of the cell’s content into the extracellular space triggers an inflammatory response which can cause further damage to surrounding cells.4 Both processes have been implicated in loss of myocardial cells in pathologies such as ischaemia/reperfusion (I/R), cardiomyopathy, and congestive heart failure.

This review discusses the mechanism(s) of mitochondrial dysfunction and how malfunctioning mitochondria might contribute to loss of cardiac myocytes.

What does mitochondria do for the heart?

Cardiac mitochondria are powerful organelles supplying energy to support the high adenosine triphosphate (ATP) consumption of the beating heart.

Which muscle cells have the most mitochondria?

What cells have the most mitochondria? A. Your heart muscle cells – with about 5,000 mitochondria per cell. These cells need more energy, so they contain more mitochondria than any other organ in the body!

Which muscle type has the largest mitochondria?

Muscle Fiber Types By Andrew Golin, Movement is one of the most distinctive characteristics of human life. Body motion is facilitated by specialized cells called muscle fibers and is controlled by our nervous system (1). Three broad classes of muscle fibers exist: skeletal, cardiac and smooth.

  • Skeletal muscle fibers are multi-nucleated long fibers that have a cross striated outer appearance under a microscope (1).
  • Skeletal muscles are voluntarily commanded, that is, humans are able to consciously control skeletal fibers.
  • This class of muscle fibers are attached to our bones by tendons, and commonly known examples of skeletal muscle fibers are the biceps and triceps.
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Cardiac muscle fibers are also cross-striated, but our autonomic nervous system, which controls our involuntary nervous system, regulates the movement of these fibers (1). Skeletal and cardiac muscles are striated due to the overlapping and crossing of myofilaments.

  • Myofilaments are chains of actin and myosin proteins, which are the predominant tissue in all muscles.
  • Unlike both skeletal and cardiac muscle fibers, smooth fibers are not striated (1).
  • Smooth muscle fibers’ activity is regulated by our autonomic nervous system.
  • The body’s organs possess the largest portions of smooth muscle fibers (1).

Muscle fibers can be further distinguished into two subcategories: slow and fast twitch fibers. Slow twitch fibers, also known as type I fibers, contain more mitochondrion and myoglobin molecules than fast twitch fibers (2). Mitochondria are organelles where biochemical processes that generate fuel for the cell through cellular respiration occur.

Myoglobin proteins are functionally similar to hemoglobin molecules. Myoglobin proteins carry and store oxygen molecules in muscle cells. Since mitochondria generate fuel from cellular respiration, oxygen molecules, being the primary reactant, type I fibers are energetically supplied by aerobic processes (2).

Fast twitch fibers, or type II fibers, have fewer mitochondrion and myoglobin proteins than slow twitch fibers (2). Despite the decreased amount of mitochondria, type II fibers are still able to synthesize large amounts of energy through anaerobic processes.

  • Anaerobic processes do not require oxygen and utilize glucose, a simple unit of sugar, as their primary energy supply.
  • Though type I and type II fibers have different sources of energy, the consequences of both energy-synthesizing processes are similar: to produce adenosine tri-phosphate (ATP), a molecule that contains large amounts of energy (2).

The body utilizes ATP as the primary source of energy currency. But before ATP can be converted into energy, the brain must send electrical impulses to muscles in order to initiate contractions (1). These electrical impulses travel rapidly across coatings or “sheaths” on the outside of the nerve cells for increased speed.

  1. Multiple sclerosis is an autoimmune disease where the body attacks its own myelin sheaths.
  2. If the damage is minor, nerve impulses will continue to travel with minimal interruptions.
  3. If the damage is sufficient to cause the myelin to be replaced with scar tissue, nerve impulses may not travel through at all (4).

Multiple Sclerosis Society of Canada’s list of symptoms include extreme fatigue, lack of coordination, weakness, tingling, impaired sensation, vision problems, bladder problems, cognitive impairment and mood changes (4). Fast twitch fibers generate quicker contractions compared to slow twitch fibers, due to the greater thickness of their myelin sheaths (3).

  1. The thicker the myelin sheath, the faster nerve impulses may travel from the brain to the muscle (3).
  2. Therefore, slow twitch fibers have thinner sheaths than fast twitch fibers (3).
  3. Once the signal reaches the muscle fibers, ATP is used in exchange for contractions.
  4. Type I fibers do not fatigue as quickly as type II fibers (2).

This is due to the different chemical by-products that arise from either aerobic or anaerobic processes. The by-products of type I fibers are carbon dioxide and water, which do not cause muscles to fatigue quickly. The primary by-product of fast twitch anaerobic processes is lactic acid.

  • Lactic acid increases the acidity of muscles and causes the fibers to fatigue quickly.
  • Staying hydrated during physical activities, breathing deeply during rest periods, and eating foods rich in magnesium will help decrease lactic acid build up during training sessions.
  • Aerobic exercises are physical activities performed at low to moderate intensity.

Common examples are jogging, swimming, cycling and walking. Anaerobic exercises are physical activities performed at high to maximum intensity. Sprinting, Olympic weight lifting and jumping are anaerobic activities. Aerobic exercises can be performed for long periods of time, where anaerobic activities are often performed in high intensity intervals.

While both forms of exercise utilize all muscle fiber types, aerobic activities utilize more slow twitch fibers where anaerobic exercises employ more fast twitch muscle fibers. By understanding which fibers are used in either aerobic or anaerobic activities, people may configure their training sessions to focus on specific muscle fibers.

Individuals involved in anaerobic activities should configure their workouts towards fast twitch development. Fast twitch development requires low volume, high intensity, and low frequency repetition schemes (3). Individuals involved in aerobic activities should alter their training sessions towards high volume, low intensity, and high frequency repetition ranges (4).

  1. By applying the knowledge above, training sessions can be configured to increase optimal specificity, and therefore optimal efficacy towards one’s goals.
  2. References: 1.
  3. Gardner, Ernest Dean, Donald James Gray, and Ronan O’Rahilly.
  4. Muscular System.” Anatomy: A Regional Study of Human Structure,
  5. Philadelphia: Saunders, 1975.28-30.

Print.2. Dreams. Muscle Fiber Types_Energy Production and Cardiovascular (n.d.): n. pag. Web.3 Oct.2015.3. “Muscle-Specific Hypertrophy: Chest, Triceps and Shoulders By Menno Henselmans.” SimplyShreddedcom,N.p., n.d. Web.03 Oct.2015.4. “Multiple Sclerosis Society of Canada.” What Is MS? — MS Society of Canada,N.p., n.d.

What advantage is the presence of many mitochondria in muscle cells?

Why do muscle cells need a lot of mitochondria? I approach this by thinking of a cell as my entire body. If I lie in bed and do nothing all day I am like a fat cell. I only need a little energy which I get from a small amount of food in the way that fat cells only a little energy which they get from a small number of mitochondria.

On active days I am like a muscle cell. I need lots of food in the way that fat cells need a lot of mitochondria to give them energy. Mitochondria are the energy factories for all cells, ATP synthesis occurs in them by ADP and Pyruvate synthesizing to create ATP, which is energy. Muscle cells work hard to move and contract and this is why they require a lot of energy thus they contain more mitochondria to produce a high level of ATP Energy is produced by respiration, the production of energy taking place in mitochondria.

Muscles need alot of energy to contract, relax. So perhaps you can begin to understand why muscles need alot of mitochondria? Mitochondria are the energy factories for all cells. ATP synthesis occurs in them by ADP and Pyruvate synthesising to create ATP, which is energy.

Muscle cells work hard and therfore require a lot of energy thus they contain more mitochondria to produce a high level of ATP. I th I approach this by thinking of a cell as my entire body. If i lie in bed and do nothing all day I am like a fat cell. I only need a little energy which i get from a small amount of food in the way that fat cells only a little energy which they get from a small number of mitochondria.

On active days I am like a muscle cell. I need lots of food in the way that fat cells need a lot of mitochondria to give them energy. I hope this helps. if you want further help with anything related to biology or require a more in depth answer do not hesitate to contact me.

This is because mitochondria produce ATP during aerobic respiration and ATP is needed for muscle to contract. Without the mitochondria the muscle wouldn’t be able to contract. If you need any more help please contact me. Like!! Really appreciate you sharing this blog post.Really thank you! Keep writing.

Muscles cells contain more mitochondria because they have to release large amount of energy quickly for movement. I need help with “Why muscle cells have more mitochondria than bone cells”? “> : Why do muscle cells need a lot of mitochondria?

What organ is the mitochondria most like?

What organ system is mitochondria similar to? The mitochondria is similar to the digestive system They both break down nutrients to produce energy Page 2 What organ system is similar to lysosomes and vacuoles?

Which organ cells have more mitochondria?

Of all the cells in human body, its the heart muscle cells with about 5,000 mitochondria per cell that contain far more mitochondria than any other organ in human body.

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Why do some muscle types have more mitochondria than others?

Power mode for muscle cells MicroRNAs regulate the formation of mitochondria in cells Muscles require a large amount of energy to function. This is provided primarily by mitochondria in cells that consume a lot of energy. We therefore find more of these powerhouses of the cell in muscle cells than in other cell types with a lower metabolic rate.

  1. Scientists at the Max Planck Institute for Heart and Lung Research in Bad Nauheim have now identified a mechanism that can be used to regulate the development of mitochondria in muscle cells.
  2. This is what makes the endurance capacity of muscles even possible in the first place.
  3. Energy is supplied to cells via two different mechanisms: by means of a process known as glycolysis, cells extract the energy carrier adenosine triphosphate (ATP) from glucose.

Oxygen is not required. The disadvantage of glycolysis is its low efficiency. For this reason, cells that require a lot of energy to function manufacture ATP primarily via the respiratory chain. This is more efficient than glycolysis. It takes place in the mitochondria and consumes oxygen.

  • Due to their relatively high energy demand, muscle cells require a particularly high number of mitochondria compared to other cell types.
  • Scientists in Thomas Braun’s “Cardiac Development and Remodelling” Department have now discovered a mechanism that controls the formation of mitochondria during muscle stem cell differentiation into functional muscle cells.

Short, non-coding RNA molecules, known as microRNAs, play a crucial role in this process, as a does a group of genes known as a mega gene cluster. Thomas Böttger, Group Leader in the Department at the Max Planck Institute explains how it works: “In stem cells, the Dlk1-Dio3 gene cluster blocks the formation of mitochondria.

What is so special about cardiac muscle compared to skeletal muscle?

Cardiac muscle differs from skeletal muscle in that it exhibits rhythmic contractions and is not under voluntary control. The rhythmic contraction of cardiac muscle is regulated by the sinoatrial node of the heart, which serves as the heart’s pacemaker.

Which muscle type has the most mitochondria?

What cells have the most mitochondria? A. Your heart muscle cells – with about 5,000 mitochondria per cell. These cells need more energy, so they contain more mitochondria than any other organ in the body!

Which muscle type has the largest mitochondria?

Muscle Fiber Types By Andrew Golin, Movement is one of the most distinctive characteristics of human life. Body motion is facilitated by specialized cells called muscle fibers and is controlled by our nervous system (1). Three broad classes of muscle fibers exist: skeletal, cardiac and smooth.

  1. Skeletal muscle fibers are multi-nucleated long fibers that have a cross striated outer appearance under a microscope (1).
  2. Skeletal muscles are voluntarily commanded, that is, humans are able to consciously control skeletal fibers.
  3. This class of muscle fibers are attached to our bones by tendons, and commonly known examples of skeletal muscle fibers are the biceps and triceps.

Cardiac muscle fibers are also cross-striated, but our autonomic nervous system, which controls our involuntary nervous system, regulates the movement of these fibers (1). Skeletal and cardiac muscles are striated due to the overlapping and crossing of myofilaments.

Myofilaments are chains of actin and myosin proteins, which are the predominant tissue in all muscles. Unlike both skeletal and cardiac muscle fibers, smooth fibers are not striated (1). Smooth muscle fibers’ activity is regulated by our autonomic nervous system. The body’s organs possess the largest portions of smooth muscle fibers (1).

Muscle fibers can be further distinguished into two subcategories: slow and fast twitch fibers. Slow twitch fibers, also known as type I fibers, contain more mitochondrion and myoglobin molecules than fast twitch fibers (2). Mitochondria are organelles where biochemical processes that generate fuel for the cell through cellular respiration occur.

  1. Myoglobin proteins are functionally similar to hemoglobin molecules.
  2. Myoglobin proteins carry and store oxygen molecules in muscle cells.
  3. Since mitochondria generate fuel from cellular respiration, oxygen molecules, being the primary reactant, type I fibers are energetically supplied by aerobic processes (2).

Fast twitch fibers, or type II fibers, have fewer mitochondrion and myoglobin proteins than slow twitch fibers (2). Despite the decreased amount of mitochondria, type II fibers are still able to synthesize large amounts of energy through anaerobic processes.

Anaerobic processes do not require oxygen and utilize glucose, a simple unit of sugar, as their primary energy supply. Though type I and type II fibers have different sources of energy, the consequences of both energy-synthesizing processes are similar: to produce adenosine tri-phosphate (ATP), a molecule that contains large amounts of energy (2).

The body utilizes ATP as the primary source of energy currency. But before ATP can be converted into energy, the brain must send electrical impulses to muscles in order to initiate contractions (1). These electrical impulses travel rapidly across coatings or “sheaths” on the outside of the nerve cells for increased speed.

  1. Multiple sclerosis is an autoimmune disease where the body attacks its own myelin sheaths.
  2. If the damage is minor, nerve impulses will continue to travel with minimal interruptions.
  3. If the damage is sufficient to cause the myelin to be replaced with scar tissue, nerve impulses may not travel through at all (4).

Multiple Sclerosis Society of Canada’s list of symptoms include extreme fatigue, lack of coordination, weakness, tingling, impaired sensation, vision problems, bladder problems, cognitive impairment and mood changes (4). Fast twitch fibers generate quicker contractions compared to slow twitch fibers, due to the greater thickness of their myelin sheaths (3).

The thicker the myelin sheath, the faster nerve impulses may travel from the brain to the muscle (3). Therefore, slow twitch fibers have thinner sheaths than fast twitch fibers (3). Once the signal reaches the muscle fibers, ATP is used in exchange for contractions. Type I fibers do not fatigue as quickly as type II fibers (2).

This is due to the different chemical by-products that arise from either aerobic or anaerobic processes. The by-products of type I fibers are carbon dioxide and water, which do not cause muscles to fatigue quickly. The primary by-product of fast twitch anaerobic processes is lactic acid.

Lactic acid increases the acidity of muscles and causes the fibers to fatigue quickly. Staying hydrated during physical activities, breathing deeply during rest periods, and eating foods rich in magnesium will help decrease lactic acid build up during training sessions. Aerobic exercises are physical activities performed at low to moderate intensity.

Common examples are jogging, swimming, cycling and walking. Anaerobic exercises are physical activities performed at high to maximum intensity. Sprinting, Olympic weight lifting and jumping are anaerobic activities. Aerobic exercises can be performed for long periods of time, where anaerobic activities are often performed in high intensity intervals.

While both forms of exercise utilize all muscle fiber types, aerobic activities utilize more slow twitch fibers where anaerobic exercises employ more fast twitch muscle fibers. By understanding which fibers are used in either aerobic or anaerobic activities, people may configure their training sessions to focus on specific muscle fibers.

Individuals involved in anaerobic activities should configure their workouts towards fast twitch development. Fast twitch development requires low volume, high intensity, and low frequency repetition schemes (3). Individuals involved in aerobic activities should alter their training sessions towards high volume, low intensity, and high frequency repetition ranges (4).

  1. By applying the knowledge above, training sessions can be configured to increase optimal specificity, and therefore optimal efficacy towards one’s goals.
  2. References: 1.
  3. Gardner, Ernest Dean, Donald James Gray, and Ronan O’Rahilly.
  4. Muscular System.” Anatomy: A Regional Study of Human Structure,
  5. Philadelphia: Saunders, 1975.28-30.

Print.2. Dreams. Muscle Fiber Types_Energy Production and Cardiovascular (n.d.): n. pag. Web.3 Oct.2015.3. “Muscle-Specific Hypertrophy: Chest, Triceps and Shoulders By Menno Henselmans.” SimplyShreddedcom,N.p., n.d. Web.03 Oct.2015.4. “Multiple Sclerosis Society of Canada.” What Is MS? — MS Society of Canada,N.p., n.d.