Module 3- Neuromuscular phys/plasticity

How does strength training effect vmax?

-eccentrics more forceful -isometrics will be more forceful -vmax shifts to left(slower)

Role of AMPK

-main energy sensor in skeletal muscle -when energy are fairly low AMPK tends to increase -plays a central role in mitochondrial biogenisis

Vmax influenced

-myosin heavy chain (MHC) -fiber length -SR/ T-tubular volume

Explain why you don't want your myofibers contracting through large range of motion when trying to run for endurance?

-range of motion= extension and flexion during running

Endurance training

Goal is to improve oxidation of fuels Muscle cell Fuels -Carbohydrate (glucose) -Fatty acids Metabolic pathways Aerobic glycolysis Beta-oxidation (6) Krebs cycle (4) ETC (5)

adaptation: mitochondria

Goal of endurance training -mitochondrial biogenesis

Internal torque

Muscle torque -not constant through the range of motion -because intrinsic properties of the muscle will cause variations in muscle force therefore causing variation in torque product of an internal force and its internal moment arm

Identify all factors that affect maximal movement speed

Muscle: -PCSA (increase power to increase GRF) -Fiber type (IIX > I) -Fiber (fascicle) length (Longer levers = more force) Tendon compliance (1) Stiffer tendons transmit more force (quick/explosive movements) (2) Stretch-shortening cycles increase force due to recoil (repetitive movements) Genetic polymorphisms (e.g., Actinin-3)

factors that affect maximal muscle strength

Muscle: PCSA, Fiber type, Fiber length, Tendon compliance Nervous System: MU recruitment and synchronization, rate coding, reflex inhibition/activation of MU (activity of GTO and spindles) Muscle Mechanics: LT and FV curves, Type of contraction, stretch-shortening cycles (spindle activation)

Muscle force and velocity(and length): optimize muscle mechanics and MU recruitment

Myofiber -need to contract slowly -to produce higher levels of force

Maximal muscle strength

*Maximal= how we assess someone's strength in an applied situation -measured through 1rm measured in the lab/ gym using 1rm -not just a single contraction -multiple lifts to optimize weight lifted -Used with major muscle group

Define fatigue

-Decrease in force production -Increased effort (more motor units) to maintain power output -Inability to produce level of expected force (NOT INJURY)

What can happen to SR Ca2+ release during high intensity exercise and how does this affect muscle force?

-Decreased Ca2+ release from SR •Due to Inorganic phosphate (Pi) accumulation -Decreases muscle force production •Decreases torque (F X MA) •Decreases power (F X V)

What are the neural adaptations to strength training?

-Early improvements to strength (up to 2 weeks) -Improvements to motor unit recruitment and rate coding -Improvements to reciprocal inhibition (E.g., decreased activity of antagonist) -Decreased sensitivity of GTO

What factors are needed for muscle hypertrophy?

-External forces greater than normal -Protein synthesis >> protein degradation -Growth hormones -Satellite Cells

Other factors affecting movement speed

-Form -drag and wind resistance (harder for larger person to move through space -energy expenditure(there is an optimal muscle mass -tendon elastic recoil (springs the stiffer the springs the greater ground reaction force and faster velocity

Why is muscle glycogen affected in most competitive endurance races?

-Glycogen and glucose are the primary fuel sources during high intensity exercise (70-90% VO2max) -Although type I fibers are preferential, competitive races will recruit and use a significant proportion of type II fibers

magnitude and quality of muscle activation (muscle recruitment) directly affects energy use and demands: endurance

-If you're able to minimize motor unit recruit it enhance your ability to have lots of endurance -Other muscle types (ff) will be recruit to maintain force

Adaptation: Capillarity endurance training

-Improved nutrient delivery -Improved waste removal -increased capillary density

Chronic adaptation to gene expression

-Increase gene expression with acute endurance training -improvements of protein function -chronic adaptation you establish new proteins that when you start to see changes in performance

De training

-Recruited and retain some myonuclei

What is muscular fatigue?

-decrease in muscle force production (decrease in myofiber force production) -increased effort(increased motor unit recruitment) to maintain the same workrate/power out put

Fatigue: effects on muscle physiology

1. Rate of force development -Ryr and CA2+ sensitivity of contractile apparatus) -Slower increase in the ability to develop force -defects are with calcium release(problems with ryanodine receptor, problems with calcium sensitivity with troponin 2. Total force developed -contractile appartus -Decrease in total force 3. Rate of relaxation -SERCA -very slow relaxation

Muscle strength: muscle factors

1. size -pcsa -myofiber=diameter(CSA) -muscle force 2.Fiber type 3. Tendon (length +compliance) -force transmission

Sites that cause fatigue

1.difficulty propagating action potentials across the sarcolemma 2.When you're doing thousands and thousands of contractions potassium tends to accumulate outside of the muscle cell, once they start to accumulate they may be able to clog these t-tubules. T-tubules invaginations within skeletal muscle that allow the action potential to get into deeper parts of the muscle. If you're clogging with potassium you're not really propagating that action potential down that muscle 3.Decreasing the chance of calcium release; if you're decreasing calcium release it's not going to bind to troponin very well 4. SERCA:calcium doesn't readily flood back into the SR 5. Contractile apparatus: The ability of myosin to walk along actin is reduced with fatigue

Factors affecting muscle force

1.muscle size (pcsa) -large pcsa will give you a large isometric force compared to a smaller muscle -muscle with larger psca will give you more force 2. Fiber type -Type I-less force less vmax -Type II- produce more (isometric force) and have a higher vmax 3. Neural activation of the muscle(recruitment/ rate coding) -synchronizing motor unit -rate coding -recruitment -If you can increase all these you can enhance the rate of force application, has huge affect on acceleration(more acceleration)

Eight week strength program : Strength gains- neural vs hypertrophy

2-3 weeks -increases in strength -not because muscle hypertrophy -what happening is you're having all these adaptations to the neural component so you're better able to recruit motor units/ motor unit fire in sync/ increase rate coding(increased activation of the muscle) -shutting down the antagonist with reciprocal inhibition 3+ weeks out -increase muscle size (hypertrophy)

muscular strength

Ability of neuromuscular system to generate a muscle torque that exceeds some external torque (e.g., 1 Repetition Maximum test using a barbell of weight).

maintenance of submaximal running velocity

Aerobic power and muscular endurance -aerobic power : vo2 max= Q x (a(arterial)-vo2) muscles ability to extract oxygen -cardiac output -extraction -O2 in system is due to the pulmonary system

Hydrogen & peripheral fatigue Aka: metabolic acidosis

Affects Ca2+ sensitivity •more calcium is required to produce pre-fatigue force -it decreases calcium sensitivity

Endurance: running economy

Athlete A -VO2 max 70ml kg/min Athlete B- vo2 max of 60min Athlete B more economical

External torque

Barbell represents external load that will exert an external torque on the system -The weight(plate) represents f=mxa(9.81 gravity*) -external load/ force associated with the load is constant External torque when lifted through the range of motion is not constant product of an external force and its external moment arm

Adaptation: physiology for endurance training

Before training: fatigue After training: preservation of force less fatigue

Endurance duration: blood glucose and muscle glycogen

Blood glucose and muscle glycogen are critically important 1st trial -Participants given just water -for about 45-to-1 hour blood glucose was maintained partly due to liver glycogen -after an hour there is a steady decline in blood glucose and muscle glycogen 2nd group -administered carbs(glucose) -Their glucose levels were maintained longer than the placebo group -it helped their glucose levels to last an extra hour then the first trial -Despite delivery of blood glucose their muscle glycogen levels still declined in both

Glycogen depletion and onset of fatigue

Glycogen depletion is also associated with peripheral muscle fatigue

Endurance: energy systems at work

Creatine Phosphate -used early on Next glycolysis -requires glucose/ or stored muscle glycogen( carbs) -produces energy at a moderately high rate but limited in its capacity Finally oxidative phosphorylation -occurs in mitochondria -requires mitochondria respiration(oxygen) -primary fuel substrates: fat, carbs, proteins(fats and carbs are the most predominant) -

Po

Maximum isometric tension

Endurance: speed vs distance

Decline in maintainable running speed with increasing distance -As distance increases average velocity decreases -Stride length decrease -grf is decreasing -The requirement for generating muscle power is still going to be lower than a faster event

Decerase type III and IV Afferent sensitivity- endurance training

Decrease Type III and IV Afferent sensitivity -Increase reflex activating metabolites -Increase group III/IV phrenic afferent discharge -Increase sympathetic efferent discharge -Decrease exercise performance

How does muscle glycogen affect muscle power?

Decreased muscle glycogen will decrease force production and therefore decrease muscle power (remember P = F X V)

Exercise Intensity

Energy System Reliance and ACSM guidelines -At fairly low exercise intensity you're primarily using fatty acids as fuel source -as exercise intensity increases the contribution from glucose tends to increase as well -Then there is a cross over point -training will shift the curve to the right you're better able to metabolize fatty acids at higher exercise intensities and sparing carbohydrates -30-60" moderate-vigorous intensity (60-90% of Hr max) for at least 5 days/week

factors affecting running economy

Environment -high altitude -heat Training -plyometrics -resistance -training phase -speed,volume, intervals,etc Physiology -maximal oxygen intake(vo2 max): maximal ability to delivery oxygen to working muscle. -adolescent development: -metabolic factors:fatigue -Influence of different running speeds: different running speeds require different grf Biomechanics -flexibility -elastic energy storage: achilles tendons store energy and then release energy from a stretched achilles tendon -mechanical factors: length-tension, force velocity relationships (type of contraction) -ground reaction force: Important for maximal speed; not important for submaximal velocity. muscle be able to maintain muscular force/torque/power in order to maintain the activity Anthropometry -limb morphology: legs are relatively thin, lower mass=less energy to swing the limbs and more economical -muscle stiffness, tendon length: muscle are springs/ The stiffer the spring the more energy return you can get from those muscles/ -bodyweight and composition: lean mass and less fat mass= less energy needed to propel the person, better heat dissipation more body weight= more heat/ decreased performance

T/F: maximal strength is measured with eccentric contractions.

False

endurance exercise intensity: Fuel for atp synthesis

Fat -at low exercise intensity - Carbs -as intensity of exercise increases carbs play a greater role -adequate blood glucose/ muscle glycogen

Factors affecting muscle velocity

Fiber type -to move faster you want the muscle fibers to shorten faster at optimal length -for a type II fiber it should be a 1/3 of its vmax -type II more power=more spee Genetic polymorphisms -actinin-3 -correlated with speed Myofiber length(fascicle length) -Longer fibers give more power/ force/more velocity

Newton's Third Law

For every action, there is an equal and opposite reaction

Adaptation: Mitochondria by fiber type

High oxidative fibers(type I and IIa fibers) -They're more mitochondrial dense -fatigue resistant -High oxidative fibers have more mitochondria then low oxidative fibers(TypeIIX) -very low intensities of aerobic training will increase the number of mitochondria in these high oxidative fibers Type IIX- For adaptations you must have a significant intensity that recruits IIX fibers -most energy supplied through glycolysis -You have to work at a higher intenisty

Primary Factors Related to skeletal Muscle Force Production:

I.Factors intrinsic skeletal muscle factors: 1.PCSA or size of the muscle: Large myofiber diameter will have a large number of force vectors acting in parallel and thus large force production. 2.Fiber Type Type IIX > IIA > I (motor unit type also affects force output due to innervation ratio). 3.Myofiber length: Long myofiber length will result in not only large Vmax (maximum shortening velocity of the myofiber) but also relatively large force output for a given concentric shortening velocity compared to a shorter myofiber of the same fiber type. 4.Tendon length and degree of compliance: The longer and more compliant the tendon, the less efficient it is at transmitting force produced by the myofibers to the bones (reducing or dampening force transmission). This really affects rate of force application and power production. HOWEVER, a slight stretch of tendon is beneficial for leg muscles during locomotion because of stretch -shortening cycles of muscle -tendons (see below). II.Factors related to the nervous system: 1.Motor unit (MU) recruitment: Increase in MU recruitment will activate a greater percentage of your muscle resulting on more myofibers and force vectors, and thus an increase in force output. 2.Motor unit rate coding: Increase in MU rate coding will result in an increase in the degree of activation of the myofibers, and thus force production by individual myofibers increases causing an increase in force output of the entire skeletal muscle. 3.Reflex inhibition or activation of MUs: Golgi tendon organ activation will decrease MU recruitment and rate coding, and thus decrease skeletal muscle force production (in the same muscle as the GTO receptor). Muscle spindle activation will increase MU unit recruitment and rate coding, and thus increase skeletal muscle force production (in the same muscle as the spindle receptors). 4.Motor unit synchronization: Increase the timing of MU recruitment will increase force production. III.Factors related to skeletal muscle mechanics: 1.Muscle length-force relationship: Muscle force production varies as a function of overlap between thick and thin filaments, and thus the number of cross- bridges (actin-myosin interaction) formed at any given time. Peak muscle force occurs when there is an optimal overlap between thick and thin filaments that allows all the myosin to engage with actin. Thus muscle force output varies depending on its length (specifically the length of the sarcomeres). 2.Muscle force-velocity relationship: Peak muscle force production during concentric contractions varies as a function of shortening velocity. Intrinsically, myofibers are their weakest at high shortening velocities when the muscle doesn't have to generate high force to move heavy objects. 3.Type of muscle contraction: Force production hierarchy- Eccentric> Isometric > Slow Concentric > Fast Concentric. Eccentric force is greater than others because 2 heads of the myosin (2 MHC) molecule are thought to be engaged with the thin filament at any given time compared to only 1 head of the myosin for isometric or concentric contractions. 4.Stretch -shortening cycles: During locomotion, ankle plantar flexor and knee extensor muscles typically experience cycles of successive eccentric (stretch) and concentric (shortening) contractions. The stretching of the skeletal muscle can activate muscle spindles which will augment force production of the subsequent concentric contraction compared to the muscle only doing a concentric contraction. Primary Factors Related Skeletal Muscle Moment Arm: Muscle moment arm is the shortest distance from the line of force application (in this case it is the muscle) to the joint axis. Muscle moment arms typically change through its range of motion. If the muscle moment arm increases, then muscle torque increases due to an increase in the efficiency of the muscle force that causes rotation of the bone about its joint axis instead of compression of the bone into the joint.

How does strength training affect the length-tension and force-velocity-power relationships?

Increase in Power is due to increase in Force -Remember: P = F X V -Fiber type transitions: IIX to IIA

muscle hypertrophy

Increase in muscle (and myofiber) size -increases diameter/csa -increase in number of myofibrils

What effects does endurance training have on skeletal muscle that enhance muscular endurance?

Increased capillarity (nutrient and waste handling) Increased mitochondrial density Increased OXPHOS activity Krebs (e.g., SDH), Beta-oxidation, and ETC (e.g., cytochrome C oxidase) Increased fatigue resistance IIA fiber types (at expense of IIX) More stored glycogen Blunt the response of Type III/IV afferents Running mechanics (e.g., stride length or running economy)

Adaptation: Glycogen endurance training

Increased intramuscular glycogen content -better regulation of blood glucose levels

Adaptations to Strength Training

Increased muscle strength (maximal force producing capability) Nervous system adaptations: -Increased MU recruitment and MU discharge frequency -Less antagonist muscle activation -Less reflex inhibition Muscle Hypertrophy: Increased myofiber diameter due to increased number of myofibrils Increased muscle work and peak capacity Increased bone and connective tissue strength Increased MHC IIa and decreased MHC IIx

Inorganic phosphate & peripheral fatigue: the source

Inorganic within the skeletal muscle is rapidly accumulating -when you start accumulating inorganic phosphate -Thousands of contractions and hydrolysis reactions -interact with the ability of myosin to creep along action(decrease force and lead to fatigue -Inorganic phosphate tends to bind with calcium precipitate which makes it very difficult for calcium to bind with troponin C (That will affect the ability of myosin to creep across actin, because it makes it very difficult to activate the contractile apparatus)

Factors affecting both muscle forze and velocity

Minimize muscle fatigue -slowing of contraction/relaxation(slower speed) -drop in force -There is a high difference in power

Lo

Isometric length

Lactate accumulation (lactic acidosis)

Lactate accumulation (lactic acidosis) does not cause fatigue, but it often accompanies fatigue

Muscle strength: movement factors

Length-tension (force) relationship -For a given muscle the muscle is at an absolute -The muscle can shorten and lengthen to some degree -working range of muscle -at relatively long sarcomere lengths ability to produce force is relatively low/ cross bridge formation is low therefore force producing capacity is low Force-velocity relationship -Force production depends on the type of "contractions) -eccentric contraction produce most force -Next strongest contraction is an isometric contraction -slow concentric -If a muscle doesn't have to generate much force to lift a load then it's contracting at its highest shortening velocity -y=isometric force -x= movement velocity(relative shortening velocity) -when moving in a positive velocity direction the muscle is shortening(concentric) -vmax= maximal shortening velocity of the muscle -negative velocity is the eccentric contractions Motor unit activation -innervation ratio may vary based on motor unit type -fiber type I,IIa, IIX -if you lift a heavier object you may recruit more motor units (increase in motor unit recruitment) -A really heavy weight will recruit all motor unit types; you'll sum up all of the motor units together, producing more force motor unit rate coding -increasing in frequency of discharge of the motor units(APS) -if frequency goes up you'll get more summation/ more force -if frequency goes down less force/summation Motor unit reflux inhibition -affects motor unit recruitment/ rate coding -sensory afferent nerves may come back and may be inhibitory -feedback from peripheral can increase the threshold receptors and reduce motor unit recruitment Joint and muscle(moment arm) -low moment arm reduces the efficiency of the muscle force in rotating the lever -as moment arm is large more efficiency in the muscle force to cause rotation -muscle torque varies in range of motion -If you're relatively weak on fiber length, velocity, or moment arm you will have to increase motor unit recruitment/rate coding -If you're at an optimal force producing length of moment then you can afford to reduce motor unit recruitment

Neural Adaptation: Cross-Over Effect aka: Contralateral strength training effect

Likely due to spillover of neural drive: -Increased MU recruitment, synchronization -Left side communicates with the right side Unlikely due to muscle-specific adaptations Myosin composition, enzymes, or circulating hormones -The point of contralateral training is to slow down muscle atrophy

Tendon Compliance

MORE compliant the tendon (e.g. stretchier), the less efficient it is at transmitting force produced by the myofibers to the bones (reducing force transmission). HOWEVER, a slight stretch of tendon is beneficial for leg muscles during locomotion because of stretch -shortening cycles

factors that affect maximal movement speed

Nervous System: -MU recruitment and synchronization -Rate coding -Increase discharge frequency, -Increase rate of force development -Reciprocal inhibition of MU Mechanics: Form, drag, energy expenditure, stride length and stride rate, ground reaction forces, body frame

Muscle glycogen levels

Once muscle glycogen levels are reduced to some critical level contractile performance will diminish For endurance duration you must be able to maintain muscle glycogen levels if you dont: - work/power output will decline -fatigue -exhaustion

Specificity of training: Fiber response

Resistance training -The goal of resistance training is muscle hypertrophy -To increase force production Endurance training -mitochondrial biogenisis

What effects rate of atp and fuel substrate use?

Running velocity -As we our velocity we increase the reliance on carbohydrates as fuel source to fuel the contraction and relaxation process Fiber type distribution -If you have more type I fibers they are more economical in terms of their ability to produce ability because they have lots of mitochondria/capillary -If you have more type II fibers fewer mitochondria, these cells rely more on glucose and glycogen for fuel. Running economy

Protein turnover: synthesis + degradation- For a person that's is on a strength training program

Same pattern Massive fed gains -soon after a meal, the muscle is primed for protein synthesis. -peak is much higher then a person who isn't on strength training -Fed gains outweigh your fasted losses -Positive nitrogen balance -positive protein synthesis -This allows skeletal muscle to grow (hypertrophy)

Type III/IV afferents: central fatigue

Sense metabolic changes -increased 02, CO2, decreased ph due to exercise -That sends signals back to the brain to shut down blood flow, if you shut down blood flow you decrease exercise tolerance because you're starving skeletal muscle of the nutrients you need to perform

genetic polymorphism

Significant percentage of individuals do not make a functional ACTN3 BUT, some top level speed athletes or weight lifters have a functional copy of this gene.(**, included in 23+me analyses)

skeletal muscle torque

Skeletal Muscle Force Production × Skeletal Muscle Moment Arm

Endurance training effect on fiber type

Switch toward slower phenotypes -increases in type IIA, increasing in type I at the the expense of type IIX

Anthropometrics

The measurement of the size, proportions, and range of motion of the human body. Mechanical advantage of longer levers -Bolt (6'5"): 41 steps with stride length of 2.44m -Gay (5'11"): 46 steps with stride length of 2.20m

Training for endurance

Training regimen: 30-60 minutes of moderate intensity (20-30 min of vigorous intensity) repetitive contractile activity (e.g., running, swimming, cycling, rowing) 0-10 scale: 5-6 =moderate or 7-8=vigorous 60-90% of HRmax At least 5 d/wk Principles Endurance measurements: Time, distance, laps, velocity, VO2max, HR

Training for Strength

Training regimen: 8-10 large muscle groups 1-3 sets of 10-15 reps (near volitional fatigue at end of each set) At least 2/week Principles: Progressive overload Periodization Specificity Reversibility Individuality Strength measurement: 1-RM / weight lifted Isometric or isokinectic torque (KinCom)

T/F: The faster runners minimize contact time and maximize their vertical force it will increase their running velocity

True

T/F: high pennation angle = high pcsa

True

T/F: muscle with larger pcsa is the strongest

True

absolute measure of force

Will be in kg or another weight

adaptations of fiber types

With endurance training -a switch in to slower phenotypes -increasing in types IIA, and type I at the expense of type IIX

Central fatigue

any defects or change that occurs at the level of the alpha motor neuron back up to the brain -motivational component: you shut down -type III and IV afferent caused by the CNS and psychological mechanisms and manifests as feeling "tired" or not wanting to go on

other factors affecting endurance

body size and composition -less work to move the person -heat dissipation: lean muscle mass/ low fat content=low surface area means they can dissipate their heat very well Form Type III and IV afferents(influence motor unit recruitment -type III responds to mechanics -type IV responds to metabolites -once respiratory muscles fatigue these afferents (Type III and IV) will then send that information and the brain will cause a response (vasoconstriction to working limb/muscles) vasoconstriction-less blood and oxygen to these muscles= fatigue -preserve respiratory muscle function

velocity

change in distance over time

Acceleration

change in velocity over time

Why intrinsic force is high during eccentrics and low during fast concentrics?

cross bridge formation -during eccentric contraction both heads are attached -during concentric only one head -Fewer cross bridges when the fiber is shortening fast(rates of attachment/detachment) -at high shortening velocity you have decrease in cross bridge formation, decrease in working stroke of the power stroke -At a slow concentric there is more cross bridges, more power stroke distance -intrinsic ability of the myofiber to produce force during shortening is highly dependent on shortening velocity as opposed to the peak force during eccentric contraction is independent of lengthening velocity

Speed

derived from Muscle Power which affects Ground Reaction Force which affects Stride Length and Rate

what contraction do muscle fibers produce most force?

eccentric contraction

Peripheral fatigue

failing muscle physiological and biochemical mechanisms produce fatigue -skeletal muscle specific changes -an issue to handle calcium: to release calcium during contraction and to take calcium back up during relaxation

power

force x velocity -force(power) y axis -velocity on x axis -on the toe off phase lots of concentric contraction -

Torque

force(mass x acceleration) x moment arm external torque= torque caused by arm + book Internal torque- created by the muscle Fxma -External and internal torque should be equal to hold the book

myonuclear domain

myonuclei is responsible for the a certain volume of a muscle fiber -the volume of cytoplasm surrounding an individual nucleus

Actinin-3

making or stabilizes fast twitch fibers -may increase glycogenolysis -sprint athletes have a functional copy of actinin 3 making them more fast twitch and quicker -endurance athletes vise versa

vmax

maximum intrinsic shortening velocity of the unloaded muscle cell -Two xx fastest -followed by 2a -slowest type 1 fiber

Myonuclear domain

myonuclei is responsible for a certain volume of a muscle fiber As muscle fibers grows in volume during muscle hypertrophy -Don't ask the myonuclei to overwork, not asking to increase myonuclear domain -instead you recruit satellite cells -increase myonuclei in a cell= increased cell volume

Peak force during eccentric contraction

not affected to a large degree

Protein turnover: synthesis + degradation- For a person that's not on a strength training program

protein turnover -the balance of protein synthesis -the building of protein -the breakdown of protein 1. Synthesis rates increase soon after a meal then decrease, and then spike again after your next meal 2. Breakdown decreases after a meal, as you fast it increase 3.When you're in a positive state that is your "fed gains" in general you're increasing protein synthesis, but it's offset by these fasted losses *If we calculated all the fed gains and fasted losses we essentially come out nitrogen on balance -we're not gaining/losing protein -we're not losing gaining/losing muscle mass -essentially flat

satellite cells

quiescent, muscle precursor cells -Sandwiched between plasmalemma and the basement membrane on the periphery of skeletal muscle -Appear almost like a myonucleus except they're quiescent they're not actively dividing They become active during -skeletal muscle injury/repair -muscle hypertrophy -satellite cells are activated when the demands for hypertrophy are met They proliferate and fuse with a muscle fiber -many more nuclei supplying a much large muscle fiber

muscle fatigue: effects of fiber type

slower twitch -fatigue resistant -highly oxidative Fast twitch -primarily glycolytic quickly tax carbohydrate stores and they will fatigue

Running velocity

stride length x stride rate -to increase running velocity increase stride length or rate -neuromuscular system -grf will determine stride length

T/F: smaller moment arm = smaller torque

true

relative measure of force

will be a percentage

Muscle force and velocity (and length)

y axis- force (%maximum) x1-velocity long sarcomere lengths -gives less than optimal force production Short sarcomere lengths -not optimal Around 2.2 is where you get optimal force production of the muscle

mechanisms of hypertrophy

•Mechanical stress (force-velocity) •Nutrients (proteins and carbs) •Anabolic hormones and growth factors (blood flow and local effects) •Protein synthesis > protein degradation •Translation vs. Transcription •Satellite cell recruitment (myonuclear domain)