Muscle hypertrophy
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Muscle hypertrophy or muscle building involves a
hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J ...
or increase in size of
skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
through a growth in size of its component cells. Two factors contribute to hypertrophy:
sarcoplasm Sarcoplasm is the cytoplasm of a muscle cell. It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of glycogen (a polymer of glucose), myoglobin, a red-colored protein necessary for binding oxygen molecules tha ...
ic hypertrophy, which focuses more on increased muscle
glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one o ...
storage; and
myofibril A myofibril (also known as a muscle fibril or sarcostyle) is a basic rod-like organelle of a muscle cell. Skeletal muscles are composed of long, tubular cells known as muscle fibers, and these cells contain many chains of myofibrils. Each myo ...
lar hypertrophy, which focuses more on increased myofibril size. It is the most major part of the
bodybuilding Bodybuilding is the use of progressive resistance exercise to control and develop one's muscles (muscle building) by muscle hypertrophy for aesthetic purposes. It is distinct from similar activities such as powerlifting because it focuses ...
-related activities.


Hypertrophy stimulation

A range of stimuli can increase the volume of muscle cells. These changes occur as an adaptive response that serves to increase the ability to generate force or resist fatigue in anaerobic conditions.


Strength training

Strength training Strength training or resistance training involves the performance of physical exercises that are designed to improve strength and endurance. It is often associated with the lifting of weights. It can also incorporate a variety of training te ...
(resistance training) causes neural and muscular adaptations which increase the capacity of an athlete to exert force through voluntary muscular contraction: After an initial period of neuro-muscular adaptation, the muscle tissue expands by creating
sarcomere A sarcomere (Greek σάρξ ''sarx'' "flesh", μέρος ''meros'' "part") is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called musc ...
s (contractile elements) and increasing non-contractile elements like sarcoplasmic fluid. Muscular hypertrophy can be induced by
progressive overload Progressive overload is a method of strength training that advocates for the gradual increase of the stress placed upon the musculoskeletal and nervous system. The principle of progressive overload suggests that the continual increase in the total ...
(a strategy of progressively increasing resistance or repetitions over successive bouts of exercise in order to maintain a high
level of effort In project management, level of effort (LOE) is a support-type project activity that must be done to support other work activities or the entire project effort. It usually consists of short amounts of work that must be repeated periodically. Examp ...
). However, the precise mechanisms are not clearly understood; currently accepted hypotheses involve some combination of mechanical tension, metabolic fatigue, and muscular damage. Muscular hypertrophy plays an important role in competitive
bodybuilding Bodybuilding is the use of progressive resistance exercise to control and develop one's muscles (muscle building) by muscle hypertrophy for aesthetic purposes. It is distinct from similar activities such as powerlifting because it focuses ...
and strength sports like
powerlifting Powerlifting is a strength sport that consists of three attempts at maximal weight on three lifts: squat, bench press, and deadlift. As in the sport of Olympic weightlifting, it involves the athlete attempting a maximal weight single-lift effor ...
,
football Football is a family of team sports that involve, to varying degrees, kicking a ball to score a goal. Unqualified, the word ''football'' normally means the form of football that is the most popular where the word is used. Sports commonly c ...
, and
Olympic weightlifting Olympic weightlifting, or Olympic-style weightlifting (officially named Weightlifting), is a sport in which athletes compete in lifting a barbell loaded with weight plates from the ground to overhead, with each athlete trying to successfully lift ...
.


Anaerobic training

The best approach to specifically achieve muscle growth remains controversial (as opposed to focusing on gaining strength, power, or endurance); it was generally considered that consistent anaerobic strength training will produce hypertrophy over the long term, in addition to its effects on muscular strength and endurance. Muscular hypertrophy can be increased through
strength training Strength training or resistance training involves the performance of physical exercises that are designed to improve strength and endurance. It is often associated with the lifting of weights. It can also incorporate a variety of training te ...
and other short-duration, high-intensity anaerobic exercises. Lower-intensity, longer-duration
aerobic exercise Aerobic exercise (also known as endurance activities, cardio or cardio-respiratory exercise) is physical exercise of low to high intensity that depends primarily on the aerobic energy-generating process. "Aerobic" is defined as "relating to, inv ...
generally does not result in very effective tissue hypertrophy; instead, endurance athletes enhance storage of fats and
carbohydrates In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or may ...
within the muscles, as well as
neovascularization Neovascularization is the natural formation of new blood vessels ('' neo-'' + '' vascular'' + '' -ization''), usually in the form of functional microvascular networks, capable of perfusion by red blood cells, that form to serve as collateral circu ...
.


Temporary swelling

During a workout, increased blood flow to metabolically active areas causes muscles to temporarily increase in size. This phenomenon is referred to as transient hypertrophy, or more commonly known as being "pumped up" or getting "a pump". About two hours after a workout and typically for seven to eleven days, muscles swell due to an inflammation response as tissue damage is repaired. Longer-term hypertrophy occurs due to more permanent changes in muscle structure.


Factors affecting hypertrophy

Biological factors (such as DNA and sex), nutrition, and training variables can affect muscle hypertrophy. Individual differences in genetics account for a substantial portion of the variance in existing muscle mass. A classical twin study design (similar to those of behavioral genetics) estimated that about 53% of the variance in lean body mass is heritable, along with about 45% of the variance in muscle fiber proportion. During puberty in males, hypertrophy occurs at an increased rate. Natural hypertrophy normally stops at full growth in the late teens. As
testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
is one of the body's major growth hormones, on average, males find hypertrophy much easier (on an absolute scale) to achieve than females, and, on average, have about 60% more muscle mass than women. Taking additional testosterone, as in
anabolic steroid Anabolic steroids, also known more properly as anabolic–androgenic steroids (AAS), are steroidal androgens that include natural androgens like testosterone (medication), testosterone as well as synthetic androgens that are structurally related ...
s, will increase results. It is also considered a
performance-enhancing drug Performance-enhancing substances, also known as performance-enhancing drugs (PEDs), are substances that are used to improve any form of activity performance in humans. A well-known example of cheating in sports involves doping in sport, where bann ...
, the use of which can cause competitors to be suspended or banned from competitions. Testosterone is also a medically regulated substance in most countries, making it illegal to possess without a
medical prescription A prescription, often abbreviated or Rx, is a formal communication from a physician or other registered health-care professional to a pharmacist, authorizing them to dispense a specific prescription drug for a specific patient. Historica ...
. Anabolic steroid use can cause
testicular atrophy Testicular atrophy is a medical condition in which one or both testicles (or "testes") diminish in size and may be accompanied by reduced testicular function. Testicular atrophy is not related to the temporary shrinkage of the surrounding scrotum, ...
, cardiac arrest, and
gynecomastia Gynecomastia (also spelled gynaecomastia) is the abnormal non-cancerous enlargement of one or both breasts in males due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Updated by Brent Wisse (1 ...
. In the long term, a positive energy balance, when more calories are consumed rather than burned, is helpful for anabolism and therefore muscle hypertrophy. An increased requirement for protein can help elevate protein synthesis, which is seen in athletes training for muscle hypertrophy. However, there is no scientific consensus on whether strength-training athletes have increased protein requirements. Training variables, in the context of strength training, such as frequency, intensity, and total volume also directly affect the increase of muscle hypertrophy. A gradual increase in all of these training variables will yield muscular hypertrophy.


Changes in protein synthesis and muscle cell biology associated with stimuli


Protein synthesis

The message filters down to alter the pattern of
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...
. The additional contractile proteins appear to be incorporated into existing myofibrils (the chains of
sarcomere A sarcomere (Greek σάρξ ''sarx'' "flesh", μέρος ''meros'' "part") is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called musc ...
s within a muscle cell). There appears to be some limit to how large a myofibril can become: at some point, they split. These events appear to occur within each muscle fiber. That is hypertrophy results primarily from the growth of each muscle cell rather than an increase in the number of cells.
Skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
cells are however unique in the body in that they can contain multiple nuclei, and the number of nuclei can increase.
Cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...
decreases amino acid uptake by muscle tissue, and inhibits protein synthesis. The short-term increase in protein synthesis that occurs subsequent to resistance training returns to normal after approximately 28 hours in adequately fed male youths. Another study determined that muscle protein synthesis was elevated even 72 hours following training. A small study performed on young and elderly found that ingestion of 340 grams of lean
beef Beef is the culinary name for meat from cattle (''Bos taurus''). In prehistoric times, humankind hunted aurochs and later domesticated them. Since that time, numerous breeds of cattle have been bred specifically for the quality or quantity ...
(90 g protein) did not increase muscle protein synthesis any more than ingestion of 113 grams of lean
beef Beef is the culinary name for meat from cattle (''Bos taurus''). In prehistoric times, humankind hunted aurochs and later domesticated them. Since that time, numerous breeds of cattle have been bred specifically for the quality or quantity ...
(30 g protein). In both groups, muscle protein synthesis increased by 50%. The study concluded that more than 30 g protein in a single meal did not further enhance the stimulation of muscle protein synthesis in young and elderly. However, this study didn't check protein synthesis in relation to training; therefore conclusions from this research are controversial. A 2018 review of the scientific literature concluded that for the purpose of building lean muscle tissue, a minimum of 1.6 g protein per kilogram of body weight is required, which can for example be divided over 4 meals or snacks and spread out over the day. It is not uncommon for bodybuilders to advise a protein intake as high as 2–4 g per kilogram of bodyweight per day. However, scientific literature has suggested this is higher than necessary, as protein intakes greater than 1.8 g per kilogram of body weight showed to have no greater effect on muscle hypertrophy. A study carried out by American College of Sports Medicine (2002) put the recommended daily protein intake for athletes at 1.2–1.8 g per kilogram of body weight. Conversely, Di Pasquale (2008), citing recent studies, recommends a minimum protein intake of 2.2 g/kg "for anyone involved in competitive or intense recreational sports who wants to maximize lean body mass but does not wish to gain weight. However athletes involved in strength events (..) may need even more to maximize body composition and athletic performance. In those attempting to minimize body fat and thus maximize body composition, for example in sports with weight classes and in bodybuilding, it's possible that protein may well make up over 50% of their daily caloric intake."


Microtrauma

Microtrauma is tiny damage to the muscle fibers. The precise relation between microtrauma and muscle growth is not entirely understood yet. One theory is that microtrauma plays a significant role in muscle growth. When microtrauma occurs (from weight training or other strenuous activities), the body responds by overcompensating, replacing the damaged tissue and adding more, so that the risk of repeat damage is reduced. Damage to these fibers has been theorized as the possible cause for the symptoms of
delayed onset muscle soreness Delayed onset muscle soreness (DOMS) is the pain and stiffness felt in muscles after unaccustomed or strenuous exercise. The soreness is felt most strongly 24 to 72 hours after the exercise. It is thought to be caused by eccentric (lengthening) ex ...
(DOMS), and is why progressive overload is essential to continued improvement, as the body adapts and becomes more resistant to stress. However, other work examining the time course of changes in muscle protein synthesis and their relationship to hypertrophy showed that damage was unrelated to hypertrophy. In fact, in one study the authors showed that it was not until the damage subsided that protein synthesis was directed to muscle growth.


Myofibrillar vs. sarcoplasmic hypertrophy

In the bodybuilding and fitness community and even in some academic books skeletal muscle hypertrophy is described as being in one of two types: Sarcoplasmic or myofibrillar. According to this hypothesis, during sarcoplasmic hypertrophy, the volume of
sarcoplasm Sarcoplasm is the cytoplasm of a muscle cell. It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of glycogen (a polymer of glucose), myoglobin, a red-colored protein necessary for binding oxygen molecules tha ...
ic fluid in the muscle cell increases with no accompanying increase in muscular strength, whereas during myofibrillar hypertrophy,
actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of over ...
and
myosin Myosins () are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The first myosin ...
contractile proteins increase in number and add to muscular strength as well as a small increase in the size of the muscle. Sarcoplasmic hypertrophy is greater in the muscles of
bodybuilder Bodybuilding is the use of progressive resistance exercise to control and develop one's muscles (muscle building) by muscle hypertrophy for aesthetic purposes. It is distinct from similar activities such as powerlifting because it focuses ...
s because studies suggest sarcoplasmic hypertrophy shows a greater increase in muscle size while myofibrillar hypertrophy proves to increase overall muscular strength making it more dominant in Olympic weightlifters. These two forms of adaptations rarely occur completely independently of one another; one can experience a large increase in fluid with a slight increase in proteins, a large increase in proteins with a small increase in fluid, or a relatively balanced combination of the two.


In sports

Examples of increased muscle hypertrophy are seen in various
professional sport In professional sports, as opposed to amateur sports, participants receive payment for their performance. Professionalism in sport has come to the fore through a combination of developments. Mass media and increased leisure have brought larg ...
s, mainly strength related sports such as
boxing Boxing (also known as "Western boxing" or "pugilism") is a combat sport in which two people, usually wearing protective gloves and other protective equipment such as hand wraps and mouthguards, throw punches at each other for a predetermined ...
,
olympic weightlifting Olympic weightlifting, or Olympic-style weightlifting (officially named Weightlifting), is a sport in which athletes compete in lifting a barbell loaded with weight plates from the ground to overhead, with each athlete trying to successfully lift ...
,
mixed martial arts Mixed martial arts (MMA), sometimes referred to as cage fighting, no holds barred (NHB), and ultimate fighting, and originally referred to as Vale Tudo is a full-contact combat sport based on striking, grappling and ground fighting, inc ...
,
rugby Rugby may refer to: Sport * Rugby football in many forms: ** Rugby league: 13 players per side *** Masters Rugby League *** Mod league *** Rugby league nines *** Rugby league sevens *** Touch (sport) *** Wheelchair rugby league ** Rugby union: 1 ...
,
professional wrestling Professional wrestling is a form of theater that revolves around staged wrestling matches. The mock combat is performed in a ring similar to the kind used in boxing, and the dramatic aspects of pro wrestling may be performed both in the ring o ...
and various forms of
gymnastics Gymnastics is a type of sport that includes physical exercises requiring balance, strength, flexibility, agility, coordination, dedication and endurance. The movements involved in gymnastics contribute to the development of the arms, legs, shou ...
. Athletes in other more skill-based sports such as
basketball Basketball is a team sport in which two teams, most commonly of five players each, opposing one another on a rectangular Basketball court, court, compete with the primary objective of #Shooting, shooting a basketball (ball), basketball (appr ...
,
baseball Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding tea ...
,
ice hockey Ice hockey (or simply hockey) is a team sport played on ice skates, usually on an ice skating rink with lines and markings specific to the sport. It belongs to a family of sports called hockey. In ice hockey, two opposing teams use ice hock ...
, and
football Football is a family of team sports that involve, to varying degrees, kicking a ball to score a goal. Unqualified, the word ''football'' normally means the form of football that is the most popular where the word is used. Sports commonly c ...
may also train for increased muscle hypertrophy to better suit their position of play. For example, a
center (basketball) The center (C), or the centre, also known as the five or the pivot, is one of the five Basketball position, positions in a regulation basketball game. The center is normally the tallest player on the team, and often has a great deal of strength an ...
may want to be bigger and more muscular to better overpower his or her opponents in the low post. Athletes training for these sports train extensively not only in
strength Strength may refer to: Physical strength *Physical strength, as in people or animals * Hysterical strength, extreme strength occurring when people are in life-and-death situations *Superhuman strength, great physical strength far above human c ...
but also in
cardiovascular The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
and
muscular endurance Endurance (also related to sufferance, resilience, constitution, fortitude, and hardiness) is the ability of an organism to exert itself and remain active for a long period of time, as well as its ability to resist, withstand, recover from a ...
training.


See also

* Anabolism *
Colorado Experiment The Colorado Experiment was a bodybuilding experiment run by Arthur Jones using Nautilus equipment at the Colorado State University in May 1973. It is of interest due to its claims that incredible results can be achieved with a small number of s ...
* Davis' law *
Lean body mass Lean body mass (LBM), sometimes conflated with ''fat-free mass'', is a component of body composition. Fat free mass (FFM) is calculated by subtracting body fat weight from total body weight: total body weight is lean plus fat. In equations: :LBM&n ...
* Muscle atrophy *
Muscle dystrophy Muscular dystrophies (MD) are a genetically and clinically heterogeneous group of rare neuromuscular diseases that cause progressive weakness and breakdown of skeletal muscles over time. The disorders differ as to which muscles are primarily affe ...
*
Myostatin Myostatin (also known as growth differentiation factor 8, abbreviated GDF8) is a protein that in humans is encoded by the ''MSTN'' gene. Myostatin is a myokine that is produced and released by myocytes and acts on muscle cells to inhibit muscle ...
* Follistatin *
Pseudohypertrophy Pseudohypertrophy, or false enlargement, is an increase in the size of an organ due to infiltration of a tissue not normally found in that organ. It is commonly applied to enlargement of a muscle due to infiltration of fat or connective tissue, ...


References


Further reading

* * * * * * * {{Strength training exercises Muscular system Tissues (biology) Physiology Exercise physiology Bodybuilding