Module 25: Muscle Tissue

Lesson 6: Exercise and Muscle Performance

Luyện Tập Thể Lực Và Hiệu Suất Cơ

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Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module Muscle Tissue.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: Muscle Tissue

acetylcholine (ACh)
neurotransmitter that binds at a motor end-plate to trigger depolarization
actin
protein that makes up most of the thin myofilaments in a sarcomere muscle fiber
action potential
change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
aerobic respiration
production of ATP in the presence of oxygen
angiogenesis
formation of blood capillary networks
aponeurosis
broad, tendon-like sheet of connective tissue that attaches a skeletal muscle to another skeletal muscle or to a bone
ATPase
enzyme that hydrolyzes ATP to ADP
atrophy
loss of structural proteins from muscle fibers
autorhythmicity
heart’s ability to control its own contractions
calmodulin
regulatory protein that facilitates contraction in smooth muscles
cardiac muscle
striated muscle found in the heart; joined to one another at intercalated discs and under the regulation of pacemaker cells, which contract as one unit to pump blood through the circulatory system. Cardiac muscle is under involuntary control.
concentric contraction
muscle contraction that shortens the muscle to move a load
contractility
ability to shorten (contract) forcibly
contraction phase
twitch contraction phase when tension increases
creatine phosphate
phosphagen used to store energy from ATP and transfer it to muscle
dense body
sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments
depolarize
to reduce the voltage difference between the inside and outside of a cell’s plasma membrane (the sarcolemma for a muscle fiber), making the inside less negative than at rest
desmosome
cell structure that anchors the ends of cardiac muscle fibers to allow contraction to occur
eccentric contraction
muscle contraction that lengthens the muscle as the tension is diminished
elasticity
ability to stretch and rebound
endomysium
loose, and well-hydrated connective tissue covering each muscle fiber in a skeletal muscle
epimysium
outer layer of connective tissue around a skeletal muscle
excitability
ability to undergo neural stimulation
excitation-contraction coupling
sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber’s sarcomeres
extensibility
ability to lengthen (extend)
fascicle
bundle of muscle fibers within a skeletal muscle
fast glycolytic (FG)
muscle fiber that primarily uses anaerobic glycolysis
fast oxidative (FO)
intermediate muscle fiber that is between slow oxidative and fast glycolytic fibers
fibrosis
replacement of muscle fibers by scar tissue
glycolysis
anaerobic breakdown of glucose to ATP
graded muscle response
modification of contraction strength
hyperplasia
process in which one cell splits to produce new cells
hypertonia
abnormally high muscle tone
hypertrophy
addition of structural proteins to muscle fibers
hypotonia
abnormally low muscle tone caused by the absence of low-level contractions
intercalated disc
part of the sarcolemma that connects cardiac tissue, and contains gap junctions and desmosomes
isometric contraction
muscle contraction that occurs with no change in muscle length
isotonic contraction
muscle contraction that involves changes in muscle length
lactic acid
product of anaerobic glycolysis
latch-bridges
subset of a cross-bridge in which actin and myosin remain locked together
latent period
the time when a twitch does not produce contraction
motor end-plate
sarcolemma of muscle fiber at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine
motor unit
motor neuron and the group of muscle fibers it innervates
muscle tension
force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions
muscle tone
low levels of muscle contraction that occur when a muscle is not producing movement
myoblast
muscle-forming stem cell
myofibril
long, cylindrical organelle that runs parallel within the muscle fiber and contains the sarcomeres
myogram
instrument used to measure twitch tension
myosin
protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fiber
myotube
fusion of many myoblast cells
neuromuscular junction (NMJ)
synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal
neurotransmitter
signaling chemical released by nerve terminals that bind to and activate receptors on target cells
oxygen debt
amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction
pacesetter cell
cell that triggers action potentials in smooth muscle
pericyte
stem cell that regenerates smooth muscle cells
perimysium
connective tissue that bundles skeletal muscle fibers into fascicles within a skeletal muscle
power stroke
action of myosin pulling actin inward (toward the M line)
pyruvic acid
product of glycolysis that can be used in aerobic respiration or converted to lactic acid
recruitment
increase in the number of motor units involved in contraction
relaxation phase
period after twitch contraction when tension decreases
sarcolemma
plasma membrane of a skeletal muscle fiber
sarcomere
longitudinally, repeating functional unit of skeletal muscle, with all of the contractile and associated proteins involved in contraction
sarcopenia
age-related muscle atrophy
sarcoplasm
cytoplasm of a muscle cell
sarcoplasmic reticulum (SR)
specialized smooth endoplasmic reticulum, which stores, releases, and retrieves Ca++
satellite cell
stem cell that helps to repair muscle cells
skeletal muscle
striated, multinucleated muscle that requires signaling from the nervous system to trigger contraction; most skeletal muscles are referred to as voluntary muscles that move bones and produce movement
slow oxidative (SO)
muscle fiber that primarily uses aerobic respiration
smooth muscle
nonstriated, mononucleated muscle in the skin that is associated with hair follicles; assists in moving materials in the walls of internal organs, blood vessels, and internal passageways
somites
blocks of paraxial mesoderm cells
stress-relaxation response
relaxation of smooth muscle tissue after being stretched
synaptic cleft
space between a nerve (axon) terminal and a motor end-plate
T-tubule
projection of the sarcolemma into the interior of the cell
tetanus
a continuous fused contraction
thick filament
the thick myosin strands and their multiple heads projecting from the center of the sarcomere toward, but not all to way to, the Z-discs
thin filament
thin strands of actin and its troponin-tropomyosin complex projecting from the Z-discs toward the center of the sarcomere
treppe
stepwise increase in contraction tension
triad
the grouping of one T-tubule and two terminal cisternae
tropomyosin
regulatory protein that covers myosin-binding sites to prevent actin from binding to myosin
troponin
regulatory protein that binds to actin, tropomyosin, and calcium
twitch
single contraction produced by one action potential
varicosity
enlargement of neurons that release neurotransmitters into synaptic clefts
visceral muscle
smooth muscle found in the walls of visceral organs
voltage-gated sodium channels
membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na+ enters through the channel
wave summation
addition of successive neural stimuli to produce greater contraction
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Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
Physical training alters the appearance of skeletal muscles and can produce changes in muscle performance. Conversely, a lack of use can result in decreased performance and muscle appearance. Although muscle cells can change in size, new cells are not formed when muscles grow. Instead, structural proteins are added to muscle fibers in a process called hypertrophy, so cell diameter increases. The reverse, when structural proteins are lost and muscle mass decreases, is called atrophy. Age-related muscle atrophy is called sarcopenia. Cellular components of muscles can also undergo changes in response to changes in muscle use.
Slow fibers are predominantly used in endurance exercises that require little force but involve numerous repetitions. The aerobic metabolism used by slow-twitch fibers allows them to maintain contractions over long periods. Endurance training modifies these slow fibers to make them even more efficient by producing more mitochondria to enable more aerobic metabolism and more ATP production. Endurance exercise can also increase the amount of myoglobin in a cell, as increased aerobic respiration increases the need for oxygen. Myoglobin is found in the sarcoplasm and acts as an oxygen storage supply for the mitochondria.

The training can trigger the formation of more extensive capillary networks around the fiber, a process called angiogenesis, to supply oxygen and remove metabolic waste. To allow these capillary networks to supply the deep portions of the muscle, muscle mass does not greatly increase in order to maintain a smaller area for the diffusion of nutrients and gases. All of these cellular changes result in the ability to sustain low levels of muscle contractions for greater periods without fatiguing.

The proportion of SO muscle fibers in muscle determines the suitability of that muscle for endurance, and may benefit those participating in endurance activities. Postural muscles have a large number of SO fibers and relatively few FO and FG fibers, to keep the back straight (Figure 1). Endurance athletes, like marathon-runners also would benefit from a larger proportion of SO fibers, but it is unclear if the most-successful marathoners are those with naturally high numbers of SO fibers, or whether the most successful marathon runners develop high numbers of SO fibers with repetitive training. Endurance training can result in overuse injuries such as stress fractures and joint and tendon inflammation.
Resistance exercises, as opposed to endurance exercise, require large amounts of FG fibers to produce short, powerful movements that are not repeated over long periods. The high rates of ATP hydrolysis and cross-bridge formation in FG fibers result in powerful muscle contractions. Muscles used for power have a higher ratio of FG to SO/FO fibers, and trained athletes possess even higher levels of FG fibers in their muscles. Resistance exercise affects muscles by increasing the formation of myofibrils, thereby increasing the thickness of muscle fibers. This added structure causes hypertrophy, or the enlargement of muscles, exemplified by the large skeletal muscles seen in body builders and other athletes (Figure 2). Because this muscular enlargement is achieved by the addition of structural proteins, athletes trying to build muscle mass often ingest large amounts of protein.

Except for the hypertrophy that follows an increase in the number of sarcomeres and myofibrils in a skeletal muscle, the cellular changes observed during endurance training do not usually occur with resistance training. There is usually no significant increase in mitochondria or capillary density. However, resistance training does increase the development of connective tissue, which adds to the overall mass of the muscle and helps to contain muscles as they produce increasingly powerful contractions. Tendons also become stronger to prevent tendon damage, as the force produced by muscles is transferred to tendons that attach the muscle to bone.

For effective strength training, the intensity of the exercise must continually be increased. For instance, continued weight lifting without increasing the weight of the load does not increase muscle size. To produce ever-greater results, the weights lifted must become increasingly heavier, making it more difficult for muscles to move the load. The muscle then adapts to this heavier load, and an even heavier load must be used if even greater muscle mass is desired.

If done improperly, resistance training can lead to overuse injuries of the muscle, tendon, or bone. These injuries can occur if the load is too heavy or if the muscles are not given sufficient time between workouts to recover or if joints are not aligned properly during the exercises. Cellular damage to muscle fibers that occurs after intense exercise includes damage to the sarcolemma and myofibrils. This muscle damage contributes to the feeling of soreness after strenuous exercise, but muscles gain mass as this damage is repaired, and additional structural proteins are added to replace the damaged ones. Overworking skeletal muscles can also lead to tendon damage and even skeletal damage if the load is too great for the muscles to bear.
Some athletes attempt to boost their performance by using various agents that may enhance muscle performance. Anabolic steroids are one of the more widely known agents used to boost muscle mass and increase power output. Anabolic steroids are a form of testosterone, a male sex hormone that stimulates muscle formation, leading to increased muscle mass.

Endurance athletes may also try to boost the availability of oxygen to muscles to increase aerobic respiration by using substances such as erythropoietin (EPO), a hormone normally produced in the kidneys, which triggers the production of red blood cells. The extra oxygen carried by these blood cells can then be used by muscles for aerobic respiration. Human growth hormone (hGH) is another supplement, and although it can facilitate building muscle mass, its main role is to promote the healing of muscle and other tissues after strenuous exercise. Increased hGH may allow for faster recovery after muscle damage, reducing the rest required after exercise, and allowing for more sustained high-level performance.

Although performance-enhancing substances often do improve performance, most are banned by governing bodies in sports and are illegal for nonmedical purposes. Their use to enhance performance raises ethical issues of cheating because they give users an unfair advantage over nonusers. A greater concern, however, is that their use carries serious health risks. The side effects of these substances are often significant, nonreversible, and in some cases fatal. The physiological strain caused by these substances is often greater than what the body can handle, leading to effects that are unpredictable and dangerous. Anabolic steroid use has been linked to infertility, aggressive behavior, cardiovascular disease, and brain cancer.

Similarly, some athletes have used creatine to increase power output. Creatine phosphate provides quick bursts of ATP to muscles in the initial stages of contraction. Increasing the amount of creatine available to cells is thought to produce more ATP and therefore increase explosive power output, although its effectiveness as a supplement has been questioned.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at openstax.org.

Long-distance runners have a large number of SO fibers and relatively few FO and FG fibers. (credit: “Tseo2”/Wikimedia Commons)

Body builders have a large number of FG fibers and relatively few FO and SO fibers. (credit: Lin Mei/flickr)

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
Script:
  1. Hypertrophy is an increase in muscle mass due to the addition of structural proteins.
  2. The opposite of hypertrophy is atrophy, the loss of muscle mass due to the breakdown of structural proteins.
  3. Endurance exercise causes an increase in cellular mitochondria, myoglobin, and capillary networks in slow oxidative fibers.
  4. Endurance athletes have a high level of slow oxidative fibers relative to the other fiber types.
  5. Resistance exercise causes hypertrophy.
  6. Power-producing muscles have a higher number of fast oxidative fibers than of slow fibers.
  7. Strenuous exercise causes muscle cell damage that requires time to heal.
  8. Some athletes use performance-enhancing substances to enhance muscle performance.
  9. Muscle atrophy due to age is called sarcopenia and occurs as muscle fibers die and are replaced by connective and adipose tissue.
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