Week 16: Understanding Muscle Growth

Explain how muscles produce force

The total amount of force produced by the muscle is governed by 2 factors: 1) How many muscle fibers are recruited. 2) How frequently the muscle fibers are activated. - Both are regulated by the part of our brain that controls movement, the motor cortex. From here, an electrical signal called an action potential is sent via your nerves down the spinal cord to the motor nerves, AKA motoneurons, in your muscles to recruit them. - Each motor neuron innervates a bundle of muscle fibers. Together, these form a motor unit, as illustrated in the image. Recruitment of the motor unit causes all the muscle fibers to contract maximally, which causes them to produce force. This is called a twitch. The total amount of force produced by the muscle thus depends on the number of recruited motor units. (P.10, Understanding Muscle Growth)

What is a more important feature to compare between a strong lifter and a weak lifter: their body frame or their lean body mass? and Why?

Their lean body mass. Anthropometric variance - differences in individual body structures - actually doesn't explain a lot of the variance in performance, especially at the elite level. The greatest difference between stronger and weaker lifters is simply that the stronger ones have more lean body mass. (P.56, Understanding Muscle Growth)

What are the 2 ways that hypertrophy occur based on components of in the muscle fibers?

There are 2 types of muscle hypertrophy, depending on which components in the muscle fibers increase in size: myofibrillar and sarcoplasmic. - Myofibrillar hypertrophy is the growth of the myofibrils (myosin and actin), the contractile components of the muscle tissue. - Sarcoplasmic hypertrophy is the growth of any other component of the muscle fibers, the sarcoplasm. (P.46, Understanding Muscle Growth)

True or False? The effect of DOMs or soreness after initial trainings are the same for everyone.

There is a great inter-individual variability in DOMS. Some people are almost always sore after training, whereas other people rarely are. Moreover, muscle groups within the same individual have the same variance and this does not appear to be related to muscle growth (P.26, Understanding Muscle Growth)

What is rate coding?

This term refers to the frequency of impulses sent to a muscle. Increased force can be generated through increasing either the number of muscle fibers recruited or the rate at which the impulses are sent. Also called frequency coding. (P.12, Understanding Muscle Growth)

True of False? The sizes of a motor unit depend on how many muscle fibers they have.

True (P.11, Understanding Muscle Growth)

True or False? If you make a muscle bigger, it will increase its ability to generate force during every movement that muscle is involved in.

True. (P.55, Understanding Muscle Growth)

True or False? The number of motor units that are recruited by an action depends on the amplitude of the action potential.

True. (P,11, Understanding Muscle Growth)

What is the process of upregulation in the context of muscle hypertrophy?

Upregulation: the process of increasing the response to a stimulus. - specifically : increase in a cellular response to a molecular stimulus due to increase in the number of receptors on the cell surface. (P.19, Understanding Muscle Growth + Merriam-Webster Medical Definition)

Explain why it's technically incorrect to say someone 'is' strong.

We talk about strength and power as traits, when they are in fact skills. Strictly speaking, a person cannot be strong or be powerful. A Powerlifter isn't strong: a Powerlifter has a strong bench press, deadlift and squat. Nor is an Olympic Weightlifter powerful: a weightlifter has a powerful Clean & Jerk and Snatch. (P.54, Understanding Muscle Growth)

What is cross-training effect?

When utilizing both concentric and eccentric movements during exercise, both agonist (muscle targeted) and antagonist (opposite muscle) muscles will be worked to a certain degree. (Google) If you only train your right biceps, your left biceps will become stronger too. Not only that, your triceps gets stronger too, even on the untrained side. (P.37, Understanding Muscle Growth)

Explain the relation between muscle strength and size. (XEM LẠI CÂU TRẢ LỜI)

You can think of muscle size as the body's engine of strength and your nervous system as the driver. Together, they determine your performance. (P.52) Muscle size is the only true trait that increases force production capacity without any limitation of movement specificity. If you make a muscle bigger, it will increase its ability to generate force during every movement that muscle is involved in. (P.55, Understanding Muscle Growth) Strength can be thought of as the sum of neural and morphological properties of muscle tissue. Specifically, muscle cross-sectional area (size) and the recruitment and firing frequency of the muscle fibers (rate coding) are key drivers of force production. Since the muscle growth rate is largely unaffected by the exercise intensity, the difference in strength development lies in neural adaptations. (P.11, Training frequency, volume & intensity)

What is Henneman's size principle?

Your brain by default only recruits low-threshold motor units by sending out low amplitude action potentials. Only when large amounts of force production are required, does the brain start recruiting the larger motor units. (P.11, Understanding Muscle Growth)

What s the difference between Structural Balance theory, Cross-training effect, Cross-education effect, and Antagonist co-activation? Give an example to illustrate the difference.

- Structural Balance: If any body part or movement pattern becomes overdeveloped, the nervous system shuts it down to prevent further imbalance. - Cross-training effect: When utilizing both concentric and eccentric movements during exercise, both agonist (muscle targeted) and antagonist (opposite muscle) muscles will be worked to a certain degree. - Cross-education effect: When the nervous system learns how to recruit your muscles on one side of your body, some of these neural. adaptations can also be used by the other side. - Antagonist co-activation: the activity of muscles with the opposite function of the prime movers. When the prime movers become stronger, it is not their activity that is restrained by the nervous system but that of the antagonists. Ex: Structural balance theory says that when your right biceps gets too strong relative to your triceps or your other arm, it is shut down. What the cross- education effect and antagonist co-activation both show is that this doesn't happen. Instead, the triceps, even the other arm, adapts along with the biceps. Basically, your body automatically maintains structural balance, although putting it this way is misleading. A better way to put it is that your body automatically maintains some strength symmetry both within a limb (e.g. triceps/biceps) and across limbs (e.g. right arm/left arm). (P. 36, 37, 38, Understanding Muscle Growth)

What is mechanotransduction?

- The cellular processes that translates mechanical stimuli into biochemical signals, allowing cells to adapt to their surroundings. The muscle fibers release growth factors like insulin-like growth factor 1 (IGF-1) and myokines like IL-6 to signal the need for repair. - Mechanotransduction (mechano + transduction) is any of various mechanisms by which cells convert mechanical stimulus into electrochemical activity. This form of sensory transduction is responsible for a number of senses and physiological processes in the body, including proprioception, touch, balance, and hearing. (P.15, Understanding Muscle Growth + Quizlet + Wikipedia)

What's the difference between a muscle fiber and a muscle cell?

- There is no difference. Because of their unique structure, muscle cells are often referred to as muscle fibers (or myocytes). (Each muscle cell possesses not just one but multiple nuclei, which are located at the outer boarders of the cell. Each nucleus controls a region of the muscle protein. You can think of the muscle cell nuclei as command centers of a region of muscle tissue.) (P.4, Understanding Muscle Growth)

What are the characteristics of Large motor units?

1) High contraction threshold 2) Have more type II muscle fibers that can produce large amounts of force but tire quickly. (P.11, Understanding Muscle Growth)

What are the characteristics of Small motor units?

1) Low contraction threshold 2) Typically have more type I muscle fibers that are better at producing low amounts of force for a long period of time. (P.11, Understanding Muscle Growth)

What are some notable components of muscle fiber?

1) Mitochondria, responsible for energy (ATP) generation. 2) Stored glycogen (2-3%) and triglyceride (~5%). 3) The sarcoplasmic reticulum (It contains ion channel pumps that can release calcium into the myofibrils, which starts muscle contractions. ) 4) Myofibrils, the contractile components that make your muscles flex. (P.5, Understanding Muscle Growth)

What are the components that defines force production capacity?

1) Morphological components: These in practice largely come down to muscle size, since size correlates with many of the other components, like internal leverage arm and pennation angle: where and in which direction your muscles pull on your bones. 2) Neurological components: This basically refers to the ability of your central nervous system, specifically your brain's motor cortex, to control your muscles. Ex: rate coding, inter-muscular coordination... (P.52, Understanding Muscle Growth) EX: Muscle force production can be compared to the speed a car can drive at. Both the structure of the engine, particularly its size (muscle mass) and the skill of the driver (efficiency of the nervous system) affect the car's top speed.

What are the 2 factors that govern the total amount of force produced by the muscle?

1. How many muscle fibers are recruited. 2. How frequently the muscle fibers are activated. (P.9, Understanding Muscle Growth)

How does acute sarcoplasmic hypertrophy happen?

A high carbohydrate diet will increase the amount of intramuscular glycogen, for example. Voila, sarcoplasmic hypertrophy. Similarly, muscle damage can cause swelling with intramuscular water retention (edema). (P.47, Understanding Muscle Growth)

What is mTOR?

A protein that helps control several cell functions, including cell division and survival, and binds to rapamycin and other drugs. mTOR is also responsible for the activation of insulin receptors and insulin-like growth factor 1 receptors. (Wiki + Google, Understanding Muscle Growth)

What is actin-myosin cross-bridge?

Actin-myosin cross-bridges, so called sliding filament model of muscle contraction, pull the muscle tissues towards each other, causing the muscle fiber to shorten and pull on its tendons. As the actin filament slides over the myosin filament, the distance between the Z-lines of the sarcomere decrease, cross- bridges are formed and the muscle shortens. (P.9, Understanding Muscle Growth)

What can explain the sign of muscle appearing larger after just one single workout?

After muscle damage, fluid and plasma proteins move into the injured tissue. This can create muscle swelling, formally called edema, and is one of the reasons your muscles may appear larger after just a single workout even though minimal actual muscle growth has yet occurred. (P.24, Understanding Muscle Growth)

What is torque?

Also known as a moment, the ability of a force to cause rotation around an axis or a joint. (P.13, Understanding Muscle Growth)

Explain how/if reducing your back muscle training volume affects muscle growth in the chest. (XEM LẠI CÂU TRẢ LỜI)

Back muscle and chest muscle are agonist and antagonist muscle to each other. Antagonist co-activation is the activity of muscles with the opposite function of the prime movers (the agonists). When the prime movers become stronger, it is not their activity that is restrained by the nervous system but that of the antagonists. The stronger the agonist gets, the weaker the antagonist contracts. (P.36, Understanding Muscle Growth)

What is DOMS?

Delayed onset muscle soreness is the pain and stiffness felt in muscles several hours to days after unaccustomed or strenuous exercise. The pain normally starts around 6 hours post-workout and peaks 48 hours after the exercise before gradually subsiding. (P.25, Understanding Muscle Growth)

Define local regulation of muscle growth

Each muscle's size is regulated almost entirely independently of others. (P.36, Understanding Muscle Growth)

True or False? Lactate, a byproduct of glucose production and glucose production increases along with exercise intensity often incorrectly referred to as lactic acid, is an acid and was long thought to be responsible for 'the burn' and fatique you feel during high repetition strength training.

False, Lactate concentration is not the cause of acidosis. During glycolysis, lactate is produced from pyruvate as part of the lactate dehydrogenase (LDH) reaction. The production of lactate consumes 2 protons. As such, lactate actually buffers against metabolic stress: it reduces rather than increases fatigue. (P.21, Understanding Muscle Growth)

True or False? The total amount of force produced by the muscle depends on only the number of recruited motor units.

False. The total amount of force produced by the muscle is governed by 2 factors: 1) How many muscle fibers are recruited. 2) How frequently the muscle fibers are activated. (P.9, 10, Understanding Muscle Growth)

True or False. Muscle cell is similar to other human cells.

False. - A muscle cell is different from any other human cell. Most human cells are round and contain one nucleus with all our DNA except some mitochondrial DNA. - In contrast, a muscle cell is a long, cylindrical cell 50 - 100 μm in diameter, which is about the diameter of a human hair. One muscle cell can span the entire length of the muscle. (P.4, Understanding Muscle Growth)

True or False? The stronger and more powerful you are, the better you are at a skill or movement.

False. Strength and power are skills, not traits. (P.54) Your nervous system becomes better at performing the specific movement you're doing, the stronger you are at that specific movement or exercises. (P.53, 54, Understanding Muscle Growth)

True or False? Training high rep lower body parts help increase anabolic hormone levels significantly, which in turn help better muscle growth and upper body parts perform better.

False. Systemic factors like acute post-workout anabolic hormone elevations play a small role in muscle growth compared to the local effects like mechanical tension. Training the lower body may slightly improve upper body training results, but not significantly. (P.33, Understanding Muscle Growth)

True or False? Core training is very important for performance of sport because it helps improve the stability and functional movement.

False. The typical 'functional training' activities like core training are "not strong predictors of performance... Despite the emphasis fitness professionals have placed on functional movement and core training for increased performance, our results suggest otherwise.". Core training also has very limited carry-over to sports, such as volleyball throwing velocity. (P.54, Understanding Muscle Growth)

True or False? Your brain by default only recruits fast-twitch fibers first for force production to react to an action and then send out slow-twitch muscle fibers to endure the action for a long-period of time.

False. Your brain by default only recruits low-threshold motor units by sending out low amplitude action potentials. Only when large amounts of force production are required, does the brain start recruiting the larger motor units. (P.11, Understanding Muscle Growth)

True or false? High rep training only leads to sarcoplasmic muscle growth and low rep training only leads to myo-fibrillar muscle growth.

False. High rep training (with blood flow restriction) and low rep training also stimulate mitochondrial and myofibrillar protein synthesis similarly, suggesting they'll induce equal myofibrillar and sarcoplasmic growth. (P.48, Understanding Muscle Growth)

True or False? You should prevent muscle inflammation to ensure quicker recovery and muscle growth.

False. Inflammation is a normal part of the muscular repair process and inhibiting this inflammation can therefore reduce muscle recovery and growth. Muscle damage generates inflammation. Damaged muscle cells release pro- inflammatory molecules that attract neutrophils, a type of white blood cells. Neutrophils destroy dead muscle cells and produce molecules that attract other inflammatory cells. Macrophages, another type of white blood cells, infiltrate the damaged muscle to remove cell debris. Additionally, macrophages secrete growth factors and other molecules which play an important role in muscle repair. The neutrophils can attack healthy cells, worsening the muscle damage, so excessive inflammation may delay muscle recovery. (P.24, Understanding Muscle Growth)

True or False? DOMs is a sign that your muscles are growing.

False. There appears to be no relation between delayed onset muscle soreness (DOMS) and muscle growth. DOMS is mostly experienced after performing exercise you're not accustomed to, such as by performing a high volume of an exercise you've never done before. (P.26, Understanding Muscle Growth)

How are muscle fibers get recruited and produce force ?

From the motor cortex, an electrical signal called an action potential is sent via your nerves down the spinal cord to the motor nerves, AKA motoneurons, in your muscles to recruit them. Each motor neuron innervates a bundle of muscle fibers. Together, these form a motor unit, as illustrated below. Recruitment of the motor unit causes all the muscle fibers to contract maximally, which causes them to produce force. (P.9, 10, Understanding Muscle Growth)

What is GAS?

General adaptation syndrome = describes how the body responds and adapts to stress. (Quizlet) When subjected to stressors, there is an 'alarm' stage characterized by cortisol release and a state of high arousal. Afterwards, a 'resistance' phase is entered characterized by anti-catabolic and anabolic processes to bolster resistance against this type of stress. (P.49, Understanding Muscle Growth)

Explain why low body fat is important for performance in weight-bearing or bodyweight sports?

Given the same muscle mass, the lower your fat mass and thereby your total bodyweight, the higher your relative strength. (P.55, Understanding Muscle Growth)

Explain why you don't have to perform lower body compound exercises first in your workouts to stimulate anabolic hormone production.

If acute post-workout anabolic hormone elevations play a direct role in muscle growth, it is small compared to the local effects like mechanical tension. The benefits also do not seem to require that the lower body is trained before the upper body or even on the same day, so the only real take-home message here is that training the lower body may slightly improve upper body training results. (P.33) Increases in systemic hormone levels do not affect availability to other trained muscle groups. So even if heavy leg training increases the effect of anabolic hormone concentration in the leg and blood, it doesn't seem to affect how much is actually taken up by the biceps. Significant muscle growth can occur without acute post-workout elevations in anabolic hormones. So anabolic hormone elevations are not a necessary condition for muscle growth. (P.31, 32, Understanding Muscle Growth)

What is repeated bout effect?

If you perform an exercise that results in DOMS and perform it again after healing, it will have less effect than from the prior times. (P.26, Understanding Muscle Growth)

How can someone get stronger without putting on any muscle?

Intermuscular coordination is the coordination between different muscles in your body. Good intermuscular coordination means that your muscles aren't holding each other back, when you are doing particular movements. If you always do the same exercises, your muscles will adapt and learn to do those specific movements more and more efficiently. Your nervous system becomes better at performing the specific movement you're doing with little transfer to other activities. (P.53, Understanding Muscle Growth) https://desmondbeckette.wordpress.com/2010/08/25/intermuscular-coordination-intra-muscular-coordination/

Why is it hard for researchers to measure hyperplasia?

It's impossible to directly count the number of muscle fibers in a human, because to study all the muscle fibers in a muscle, you'd need to take it out of the body. So we're limited to studying corpses and of course it's hard to assess strength training effects in a corpse, as you only have the 'after' measurement without any baseline to compare it to. Even in corpses, counting the number of muscle fibers directly is like trying to count the number of hairs on someone's head: nigh impossible. The muscle fiber count of human muscles is estimated to lie in the hundreds of thousands. (P.40, 41, Understanding Muscle Growth)

What is hyperplasia?

an increase in number of muscle fibers (=muscle cells) (P.40, Understanding Muscle Growth)

What is the primary stimulus for muscle growth?

Mechanical tension. The primary stimulus for muscle growth is sufficiently high and prolonged tension created by the actin-myosin cross-bridges of muscle fibers. In other words, muscle hypertrophy occurs when enough biomechanical tension is created by the muscle fibers that their structural integrity is compromised. As an adaptive response to this stress, the muscle fibers undergo changes in their structure, including growth of the muscle fibers to be able to produce more tension in the future. (P.15, Understanding Muscle Growth) The primary type of stress inducing muscle growth is mechanical tension on the muscle fibers. Muscle damage, metabolic stress and exercise induced anabolic hormone elevations have been postulated to play a role as well, but their supporting evidence is much less compelling. (P.59, Understanding Muscle Growth)

What is a tetanic contraction?

Most movements last much longer than a single muscle twitch, so they require a continuous stream of action potentials to maintain muscle tension and complete the movement. Such a continuous contraction is called a tetanic contraction. (P.12, Understanding Muscle Growth)

Explain which mechanism(s) of muscle growth you should target with your strength training program.

Muscle Hypertrophy Muscle growth can occur via muscle hypertrophy and hyperplasia. - Hypertrophy is an enlargement of contractile elements (the myofibrils composed of myosin and actin that are inside the muscle cell). - Hyperplasia is an increase in the number of muscle fibers (= muscle cells). There is no strong evidence that muscle hyperplasia occurs in humans, especially not without assistance of growth enhancing drugs. If it does, its contribution to total muscle growth is probably small and we don't know how we could target this with training. In practice, we should thus focus on maximizing muscle fiber hypertrophy. Any hyperplasia that may occur will probably come along for the ride naturally. (P.40 & P.43)

True or False? Muscle damage is required for muscle growth.

Muscle damage is not required for muscle growth and muscle damage does not correlate with muscle growth. In fact, excessive levels of muscle damage seem to put new muscle growth on hold, causing 'overtraining'. (P.25, 26, Understanding Muscle Growth) Muscle damage can also impair muscle growth indirectly by decreasing strength performance. Damaged muscle fibers exhibit lower motor unit firing rates. This is a type of local fatigue, as it does not affect the contralateral limb. After intensive, novel training sessions, muscle force production is often impaired for 48-72 hours in trained individuals. In untrained individuals or after extremely muscle damaging workouts, performance may suffer for 2 full weeks. (P.26, Understanding Muscle Growth)

What are the 2 ways that muscle can grow?

Muscle growth can occur via muscle hypertrophy and hyperplasia. - Hypertrophy is an enlargement of contractile elements (the myofibrils composed of myosin and actin that are inside the muscle cell). - Hyperplasia is an increase in the number of muscle fibers (= muscle cells). (P.40, Understanding Muscle Growth)

Which is bigger: a myofibril or a myofilament?

Myofibril is bigger. (Each myofibril is about 1 μm in diameter. The components of myofibrils - the myofilaments myosin and actin - are responsible for the contraction of the muscle cell. Myosin and actin filaments are organized to form the smallest contractile unit of the muscle, the sarcomere) (P.5, Understanding Muscle Growth)

What is myonuclear addition?

Once the extent of muscle hypertrophy starts to exceed the myo-nuclear domain, myonuclear addition gradually occurs to support further growth. These myonuclei cannot be created by the cell itself. Instead, they are donated by satellite cells. When the muscle fiber becomes damaged, the satellite cells activate, clone themselves, and fuse to the damaged site to patch it up. In this process, their cell nucleus can be incorporated into the muscle fiber, increasing its myonuclear number. (P.19, Understanding Muscle Growth)

Define "performance" in sport and fitness

Performance generally refers to the ability to produce force during a given movement (= F in physics). (P.51, Understanding Muscle Growth) It also applies in most sports: more force equals a faster sprint, a stronger punch, a higher jump, etc. Even an elderly person that has trouble standing up straight without shaking is often a matter of force. When we informally talk about 'losing balance', physically the problem is that the person cannot produce enough force during the desired movement. That's essentially the same obstacle as not having enough strength and in both scenarios, strength training improves performance. (P.51, Understanding Muscle Growth)

What is a muscle twitch?

Recruitment of the motor unit causes all the muscle fibers to contract maximally, which causes them to produce force, which is called a twitch. (P.9, 10, Understanding Muscle Growth)

What is the sarcoplasm?

Sarcoplasm is the cytoplasm of the muscle fiber. It's the fluid the myofibrils are located in. It contains many components, among them contractile components, other proteins, mitochondria, stored glycogen and fat particles. (P.46, Understanding Muscle Growth)

What is sarcoplasmic hypertrophy?

Sarcoplasmic hypertrophy is the growth of any other component of the muscle fibers, the sarcoplasm. (P.46, Understanding Muscle Growth)

Why is muscle growth via the addition of sarcomeres in series physiologically limited?

Since muscles are affixed to your bones on their ends, there is an obvious limit on how long a muscle can become while remaining functional. (P.44, Understanding Muscle Growth)

What is the SAID principle?

Specific Adaptation to Imposed Demand. It means that when the body is placed under some form of stress, it starts to make adaptations that will allow the body to get better at withstanding that specific form of stress in the future. (Google, Lecture, Understanding Muscle Growth)

What are satellite cells?

- Satellite cells are otherwise quiescent (inactive) stem cells that are not fully differentiated into a specific role yet: 'baby cells'. They lie just outside their parent muscle fiber. They are involved in the growth and development of skeletal muscle and in muscle's adaptation to injury, immobilization and training. - When the muscle fiber becomes damaged, the satellite cells activate, clone themselves, and fuse to the damaged site to patch it up. (Quizlet + P.19, Understanding Muscle Growth)

What are the 2 ways that hypertrophy occur based on direction?

1) The addition of sarcomeres in series, resulting in a lengthening of the muscle fibers 2) In parallel, resulting in an increase in the muscle's thickness as more muscle fibers are packed together next to each other. (P.44, Understanding Muscle Growth)

What is functional training according to most people?

'Functional training' according to many people refers to some measure of transferability of performance across activities ('carry-over'). An activity is functional if it improves performance, defined below, in many other activities. So a leg extension is generally regarded as less functional than a squat, because leg extension strength doesn't transfer as well to many other activities, whereas a strong squat makes you better at jumping, sprinting, etc. (P.51) Functional training requires an activity to have a high degree of transferability of force production across various movements. (P.52, Understanding Muscle Growth)

Explain why all exercise that stimulates muscle growth can be functional.

'Functional training' according to many people refers to some measure of transferability of performance across activities ('carry-over'). An activity is functional if it improves performance, defined below, in many other activities. Performance generally refers to the ability to produce force during a given movement (= F in physics) So functional training requires an activity to have a high degree of transferability of force production across various movements. What defines force production capacity? The body's ability to produce force during a given movement - strength - has 2 components: morphological and neurological. You can think of muscle size as the body's engine of strength and your nervous system as the driver. Together, they determine your performance. The nervous system is highly movement specific in its function. Your nervous system becomes better at performing the specific movement you're doing with little transfer to other activities. That leaves muscle size as the main component of functional capacity. Muscle size is the only true trait that increases force production capacity without any limitation of movement specificity. If you make a muscle bigger, it will increase its ability to generate force during every movement that muscle is involved in. (P.51 - 55, Understanding Muscle Growth)

Define antagonist co-activation and give an example

- Antagonist co-activation is the activity of muscles with the opposite function of the prime movers (the agonists). - When the prime movers become stronger, it is not their activity that is restrained by the nervous system but that of the antagonists. Ex: So during a curl, the stronger your biceps gets, the weaker your triceps contracts. The motor cortex, the part of your brain that controls movement, learns to maximally contract the biceps during a curl with minimal interference from the triceps. (P.36, Understanding Muscle Growth)

What is an internal torque?

- Internal torque is the product of the muscle's force production and its lever arm: the distance between the center of rotation and the muscle's attachment on the bone. - When internal torque production is high enough to overcome the external resistive torque (usually from gravity acting on whatever you're lifting), the joint can move. (P.13, Understanding Muscle Growth)

What is metabolic stress?

- Metabolic stress is a physiological process that occurs during exercise in response to low energy that leads to metabolite accumulation [lactate, phosphate inorganic (Pi) and ions of hydrogen (H+)] in muscle cells along with hypoxia, i.e. the oxygen shortage, during exercise. (P.21) - Metabolic stress is particularly high during exercise with a large demand for glucose and you feel it in part as 'the burn' in your muscles. (P.21, Understanding Muscle Growth)

How does mTOR effect muscle growth and protein synthesis?

Step 1: The mTOR master enzyme in muscle cells integrates 4 major signals - growth factors, energy status, oxygen level and amino acid concentration - to regulate muscle cell growth. It sends this information to your genes residing in the cell's nuclei, which function much like command centers. Most cells only have one nucleus, but muscle cells have many. Step 2: Inside your cell's nuclei lies a molecule called deoxyribonucleic acid (DNA). DNA has 2 intertwined DNA that form a double helix with biological data that contain the blueprint to create your whole body. Based on the input from mTOR, parts of your DNA containing the information to create the desired proteins to remodel the cell are transcribed ('copied') into ribonucleic acid (RNA). Messenger RNA (mRNA) is then sent out to the ribosomes outside the nucleus in the cell's cytoplasm to produce the desired proteins. Ribosomes are the translational machinery than turns mRNA information into actual new proteins. These proteins are incorporated into the muscle fiber, allowing it to grow. (P.18, Understanding Muscle Growth)

Explain simply how muscle damage and adapt to deal with future stress.

Sufficiently heavy muscular contractions cause enough tension to damage the muscle, in addition to metabolic stress resulting from rapid energy production, metabolic waste product formation and oxygen shortage. In evolutionary terms, this fatigue constitutes a form of stress that forms an incentive for the muscle to adapt to protect itself from this stress in the future. This adaptation process is not unique to muscle tissue. Almost all bodily tissues adapt to stressors These processes called General Adaptation Syndrome (GAS). When subjected to stressors, there is an 'alarm' stage characterized by cortisol release and a state of high arousal. Afterwards, a 'resistance' phase is entered characterized by anti-catabolic and anabolic processes to bolster resistance against this type of stress. (P.49, Understanding Muscle Growth)

What is acidosis?

The acidosis is caused by hydrogen ions (H+). Every time ATP is broken down to ADP and P(i), a hydrogen ion is released. When there is enough oxygen available, these protons are used by the mitochondria during oxidative phosphorylation. However, when the demand for ATP is too large to sustain via aerobic pathways, ATP has to be regenerated via glycolysis and the phosphagen system, causing hydrogen ion accumulation, which causes increased acidity in the cell. (P.21, Understanding Muscle Growth)

What is anatomical cross-sectional area (ACSA)?

The area of the cross-section of a muscle along its longitudinal axis. Note: the blue line in the picture. (P.45, Understanding Muscle Growth)

What is physiological cross-sectional area (PCSA)

The area of the cross-section perpendicular to the direction of the muscle fiber. Note: PCSA is better correlated with force production than ACSA, because it takes into account the leverage of the muscle fibers, though not all research supports that PCSA is a better measure of strength than ACSA. (P.45, Understanding Muscle Growth)

Compensatory hypertrophy

The enlargement of a remaining organ or tissue after a portion has been surgically removed or rendered inactive. (Quizlet) When you remove a muscle with the same function or even a division (head) of the same muscle, what is left becomes stronger. The body adapts without concern for anything but function. Lost half of your calves? Better learn to walk on the other half. (P.38, 39, Understanding Muscle Growth)

What is relative strength?

The maximum force the muscles can generate in relation to your body weight. This type of strength is important for individuals who have to move their entire body weight like gymnasts. (Quizlet) The amount of strength to body size, or how strong someone is compared to their size. (Google)

What is the myonuclear domain?

The maximum region of the cell that the nuclei in the muscle fibers (myonuclei) seem to control. (P.19, Understanding Muscle Growth)

Explain how muscles produce movement.

The muscular system works with the skeletal system to allow movement. Like all muscles, the muscles that produce movement are made up of individual cells called muscle fibers. These fibers contain Myofibrils, the contractile components that make your muscles flex. Myosin and actin filaments are organized to form the smallest contractile unit of the muscle, the sarcomere. Sarcomeres occur over the entire length of the muscle fiber and are connected through actin filaments. Muscles are organized into progressively smaller units of contractile tissue: fascicles > muscle fibers > myofibrils > sarcomeres > myofilaments Actin and myosin form actin-myosin cross-bridges that pull the muscle tissues towards each other, causing the muscle fiber to shorten and pull on its tendons. The tendons transfer this force to your bones, causing your body to move. (P.9, Understanding Muscle Growth)

How does the process of myo-nuclear addition explain the phenomenon of muscle memory?

The myonuclear addition seems to be (near) permanent, thus up-regulating the muscle fiber's capacity for protein synthesis for many years. This explains the phenomenon of muscle memory: atrophied muscle still has its former peak myonuclear number, which facilitates rapid protein synthesis back up to its former size when someone starts training again (P.19, 20, Understanding Muscle Growth)