Adaptations to resistance training
Transcription
(genetics) the organic process whereby the DNA sequence in a gene is copied into mRNA happens in the nucleus
***Increases in muscle size can be detected by 21 days***
***Hypertrophy is due to increased myofibrillar content***
Skeletal hyperplasia or branched fibers
***In reality fibers tend to split, they don't make new fibers in response to lots of growth*** You're not making a new fiber but they can split
Increased neural drive
***Neural drive refers to the combination of motor unit recruitment and the rate coding of the units*** Neural drive starts in the CNS and is spread to muscle fibers through peripheral nerves Electromyography EMG using surface electrodes over the muscle measures the total activity within the nerve and muscle and therefore is a good measure of neural drive
Power is actually generated at a specific point of our strength continuum
***Peak power occurs at ~25% of strength max and ~40% Velocity max*** We can increase power by increasing our ability to move that same object by increasing the amount of strength we have. If we can move the same weight faster or a heavier weight faster, you have increased power ***Higher max strength will generate higher power***
RE and AAs stimulate signaling via mTOR
***The rate of protein synthesis within the myofibrils is controlled primarily by an enzyme known as mTOR (mechanistic target of rapamycin)*** mTOR integrates the input from upstream pathways, inclusing insulin and growth factors and amino acids, and controls transcription of mRNA -if mTOR is blocked experimantally, resistance ex does not result in muscle hypertrophy the primary stimulus for protein synthesis is the mechanical stretch applied to the muscle, which activates mTOR -mTOR senses cellular nutrient and oxygen levels, so it is also activated by the proper timing of protein intake
Strength gains may result from changes in the connections between motor neurons located in the spinal cord, allowing motor units to act more synchronously
***This increased synchronicity means that a greater number of motor units will be firing at only one time, facilitating contraction and increasing the muscles ability to generate force*** -There is good evidence to support increased motor unit synchronization with resistance training; the synchronization does improve the rate of force development and the capability to exert steady forces
power
***\how fast strength is produced*** -Explosive aspect of strength (RFD) ***Power = work/time = (force x distance)/time ->(Force x velocity)*** Power is more important than absolute strength for many activities, because sports are dynamic and things happen quickly
in animals
-Hyperplasia has been shown depending on the animal model -Main variable is loading pattern (weight, time, constant vsintermittent)
Timing of AA ingestion is critical for muscle hypertrophy
12 weeks of RE for this study The group that ingested proteins immediately post ex had larger changes in CSA than people taking it 2 hours after
RE can reverse some of the aging-associated muscle atrophy
85 year old pretraining vs 12 weeks of RE -10% increase in CSA, 130% increase in 1 RM
Proteins are composed by amino acids
Amino acid chains are assembled in a specific sequence
Power velocity relationship and performance
At higher velocity lower strength and vice versa How much strength is required to train that specific discipline -If you have a power athlete, training with heavy weight will be detrimental, because they will not shift the curve to the right. They need to generate the force at the speed whey need in the particular sport
Steps in protein synthesis
DNA -> MRNA -> Protein When we ex, our genetics dictate what mRNA our muscles are going to make (every cell in the body has the same genome, but all cells are different). The cell makes specific MRNA during protein synthesis and makes specific proteins Every time we ex, we make a copy of our genetic info in the form of MRNA and is read by ribosomes and each amino acid is added according to these instructions
Hyperplasia: increases in the number of muscle fibers
Does not happen in humans!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
three groups of amino acids
Essential: our body cannot make Nonessential: our body an make Conditionally essential: under some circumstances they are considered to be essential (physical stress like sepsis might require we obtain these)
Amino Acids stimulate muscle protein synthesis
Even at rest, essential amino acids can stimulate muscle protein synthesis EAA are necessary for muscle protein synthesis
Myofibrillar disruption can be of different magnitudes depending on how strong the stimulus is
Extent of disruption is proportional to force produced and training state Focal: minimal discomfort Moderate: disrupting lots of sarcomeres Extreme: bad, damaging type of situation, causes problems
Absolute volume of myofibrils increases; we synthesize more protein and made larger fibers -Hypertrophy is due to increased myofibrillar content
How does this happen? - When we train we stress the myofibril
resistance is not equal to the force (dynamic contractions)
In the form of shortening or lengthening contraction -Most sport activities follow a combination of these two resistance > force: lengthening contraction resistance < force: shortening contraction
Fiber splitting may appear as hyperplasia
Likely occurs through fiber splitting due to training pathology A large fiber can have smaller branches emerge -This could be confused with hyperplasia ex: If you take a muscle biopsy from a bodybuilders traps, the little fibers often seen in animal fibers can also be seen in humans -We are not making new diners, the fibers that are very large tend to split, which can look like hyperplasia Long term overload can result in the splitting of the muscle fibers
in humans
Most muscle mass gains are due to hypertrophy -All fiber types can increase in size Fiber hyperplasia may occur in certain individuals under certain conditions When it comes to muscle gains however, hyperplasia is not the main driver at all***
synchronization and recruitment of additional motor units
Motor units are generally recruited asynchronously; they are not all engaged at the same instant. -They are controlled by a number of different neurons that can transmit either excitatory or inhibitory impulses recall that Whether the muscle fibers contract or stay relaxed depends on the summation of the many impulses received by the given motor unit at any one time -The motor unit is activated and its muscle fibers contract only when the incoming excitatory impulses exceed the inhibitory impulses and the threshold is met or exceeded
Muscular factors contributing to strength development
Muscle hypertrophy
Neural Factors vs Hypertrophy
Neural factors begin to increase muscle strength early in the training progress. Eventually this plateaus and the muscles begging to accommodate to increase strength -In the early weeks you have neural adaptations that increase muscle strength with little increases in hypertrophy (the emg will show a higher signal in training at the beginning, more neural stimulation and motor unit firing rates) At some rate, you will increase your ability to produce force without neural changes, this is attributable to the muscles check chart
Increased coordination of agonist muscles
Other neural factors can contribute to strength gains with resistance training; one of these is referred to as coactivation of agonist and antagonist muscles. If both the agonist and antagonist were contracting with equal force, no movement would occur -Thus, to maximize the force generated by an agonist, it is necessary to minimize the amount of coactivation Reduction in coactivation could explain a portion of strength gains attributed to neural factor
Hypertrophy vs hyperplasia
People thought for a number of years that we would make more muscle fibers (hyperplasia -from animal studies
translation
Process by which mRNA is decoded and a protein is produced happens in the ribosome
Muscle proteins are in constant turnover
Protein turnover is the balance between synthesis and degradation ***Resistance exercise increases protein synthesis > than degradation thus resulting in a net gain of muscle (contractile) tissue.*** -Broken down and made back stronger overtime
force maintained at constant velocity
Rare, isokinetic action Isokinetic exercise is a type of strength training. It uses specialized exercise machines that produce a constant speed no matter how much effort you expend. These machines control the pace of an exercise by fluctuating resistance throughout your range of motion. Your speed remains consistent despite how much force you exert.
The best way to increase muscle size and strength in humans is to lift weights
The cross sectional area in a leg of a 24 year old vs 64 ya brings about a reduction in 40% of force reduction -Training can make you much stronger at an old age in a quick time span 24 year old vs 64 year old -20% decrease in CSA, 40% drop in Force
Z-disc snapping may lead to fiber splitting
The force can cause a snap in what holds the z disc together, when these areas snap, at some point they will start to split and as you continue training this may develop into a separate branch of the existing fiber
Increased rate coding of motor units (firing rate)
The increase in neural drive of alpha motor neurons could also increase the frequency of discharge, or rate coding, of their motor units -***Rate coding allows your muscles to develop more force by enhancing the frequency at which the neural signals get sent to your muscles telling them to contract.*** -Recall that as the frequency of stimulation of a given motor unit increases, the muscle eventually reaches a state of tetanus, producing the absolute peal force or tension of the muscle fiber or motor unit
Early strength gains are mainly driven by neuromuscular adaptations
The major drive of initial changes in muscular strength is the neural mechanisms -The change in CSA is not very large, even though the increase in muscle strength is 42% most of the early gains in strength are the result of learning how to more effectively produce force; this learning effect can account for as much as 50% of early strength gains
neural adaptations
The neuromuscular system is one of the most responsive systems in the body to the repeated stimulation of training -However, most of the early gains in strength are the result of learning how to more effectively produce force; this learning effect can account for as much as 50% of early strength gains An important component of the strength gains that result from resistance training, especially in the early stages, are neural adaptations. -Strength gains can be achieved without structural changes in the muscle but not without neural adaptations; thus, strength is not solely a property of muscle, but rather a property of the neuromuscular system
RE disrupts sarcomeres due to high force contractions
The sarcomere becomes deformed and disrupted, protein synthesis will have to repair this -Muscle soreness is these damaged sarcomeres
Training for strength and power: intensity and volume
There is a reverse relationship between the amount of work you an do and the percentage of 1 RM you are working at -Like benching 1 rep or 50 depending on the weight
An alternate explanation for neurally mediated strength gains is simply that more motor units are recruited to perform the given task, independent of whether these motor units act in unison -Such improvement in recruitment patterns could result from an increase in neural drive to the alpha motor neurons during maximal contraction
Trained muscles generate a given amount of submaximal force with less EMG activity, suggesting a more efficient motor unit recruitment pattern
autogenic inhibition
Training can reduce the inhibitory impulses like muscle spindles and golgi tendon organs -Can generate more tension without being limited by the body add more from his slides
Two types of hypertrophy can occur: transient and chronic.
Transient hypertrophy is the increases muscle size that develops during and immediately following a single exercise bout -This results mainly from fluid accumulation in the interstitial and intracellular spaces of the muscle that comes from the blood plasma, pump Chronic hypertrophy refers to the increase in muscle size that occurs with long-term resistance training -This reflects actual structural changes in the muscle that can result from an increase in the size of existing individual muscle fibers (fiber hypertrophy)
Inhibitory mechanisms in the neuromuscular system, such as the golgi tendon organs, might be necessary to prevent the muscled from exerting more force than the bones and connective tissues can tolerate -This control is referred to as autogenic inhibition
When the tension on a muscle's tendons and internal connective tissue structures exceeds the threshold of the embedded golgi tendon organs, motor neurons to the muscle are inhibited; that is,autogenic inhibition occurs. ***Resistance training can gradually reduce or counteract these inhibitory impulses, allowing the muscle to achieve a greater force production independent of muscle mass*** -Thus, strength gains may be achieved by reduced neurological inhibition
For many years, strength gains were assumed to result directly from increases in muscle size (hypertrophy).
While there is an association between size and strength, muscle strength involves far more than mere muscle size -Size is extremely important; however, the mechanism associated with strength gains are more complex Motor unit recruitment, frequency of motor nerve firing rates, better synchronization of motor units during a particular movement, and other neural factors are important to strength gains
RE stimulates muscle protein synthesis
You need to train and provide the stimulus for protein synthesis Amino acids are made to assemble actin and myosin, which will attribute to an increase in sarcomeres ***Protein synthesis rates increase very rapidly after ex, this elevation remains for at least 48 hours.*** - You need to rest at least 48 hours before you hit that muscle again or you interfere with protein synthesis
You can increase your ability to increase force in a single session
Your ability to increase muscular strength can happen in a very short period of time, at the beginning, it is just motor units activating better and more coordinated to produce force -Can make the motor neurons fire more frequently. Firing rate is the main reason why we can get stronger in a short period of time
Strength
absolute force that a muscle or muscle group can produce -Force: change in an object with mass that modifies its velocity -Tested 1 RM: maximal weight that can be lifted with a single effort -strength can be determined with a cable tensiometer
Strength-endurance
capacity to produce force during repeated muscle contractions (or sustain a single contraction) over time. Number of repetitions at given % 1RM -Influenced by gains in muscle strength, local metabolic efficiency and cardiovascular function.
Force needs to be trained specifically with the way force is being expressed in that sport (think about dominant motor abilities continuum)
example Resistance = force: Isometric contractions -rings in gymnastics
In parallel
it increases the cross section of the muscle, more cross bridges generating force at the same time Make more actin and myosin and arrange them in parallel, more hands pulling the muscle to contract
In series
makes the fiber able to generate force faster, makes you quicker You will shorten faster in series
Mechanisms of strength development
neural adaptations; changes in the central and peripheral nervous system -How do things change in the brain, sensory mechanisms, signals coming down to the muscles, activations of motor units -specific changes in EMG muscle adaptations; Changes in the muscles themselves in size and csa -Tissue will start to adapt, add more sarcomere to produce more force or power
neural adaptations.
synchronization and recruitment of additional motor units increased rate coding of motor units increased neural drive autogenic inhibition other neural factors (reduced coactivation)
resistance exercise and protein intake are powerful stimulators of skeletal muscle protein synthesis
the rate of protein synthesis within the myofibrils is controlled primarily by an enzyme known as mTOR. -the primary stimulus for protein synthesis is the mechanical stretch applied to the muscle, which activates mTOR through a signaling pathway involving I-GF1
the change in muscle size is called hypertrophy, or an increase in muscle size (because of an increase in size of the existing fibers)
we do not increase the number of our muscle fibers (hyperplasia).
insulin stimulates protein synthesis from available amino acids by promoting a more efficent conversion of genetic codes carried by mRNA into proteins, a process known as translation -this process is accomplished by ribisomes, so it stands to reason that increasing ribosome content in the muscle fibers (increasing the translational capacity) will also result in more protein being synthesized Ribosome biogenesis, the creation of new ribosomes, appears to be an important mechanism regulating muscle size in response to resistance exercise
when the synthesis of new ribosomes is blocked biochemically, muscles fail to undergo hypertrophy notably, recent studies show that mTOR is involved in the synthesis of ribosomes in the cell nucleus in addition to its role in regulating translation in the cytoplasm
Neural factors contributing to strength development, from his slides
•Increased fiber recruitment •Some neural circuits may be altered to produce high strength •Normal intrinsic inhibitory mechanisms -Inhibit muscle contraction if muscle/tendon tension too high to avoid damage training can reduce inhibitory impulses •Muscle spindles and Golgi tendon organs tolerate more stretch •Muscle can generate more force •May explain superhuman feats of strength •May increase the risk of injuries!!
