Lecture 12_ Muscle Adaptation

What stimulates muscle adaptation?

-exercises (reps)

-lift weights (strength training)

-cardiovascular/ endurance training

things cause muscle adaptation that

We don't want?

-immobilization (laziness)

-injury (muscle,tendon,bone,nerve,neurological issue)

-surgery (changing moment arms)

-electrical stimulation (chronic or intermittent)

-stretching the fibers

Slow muscle contracts more

slowly and is resistant ta fatigue

Fast muscle contracts more

rapidly out fatigues quickly

slow muscle

aerobic

fast muscle

anaerobic

white meat, dark meat

not found in human but separation based

on slow or fast twitch muscles

diff muscle fibers is why they taste dif and diff

textures because one is slow and one is fast twitch

meat is just muslcle

Dark meat

- chicken thighs (more likely to be resistant to fatigue so slow twitch)

white meat- chicken breast(fast twitch fueled by glycogen)

white meat

- chicken breast(fast twitch fueled by glycogen)

In mammals, fast and slow fibers are

mixed within muscles

no white meat vs, dark meat choices in a cow....

Different muscles have

different composition

- longer fibers...higher velocities...faster muscle

histolgy 

detemierming which fibers are fast or slow twitch

Preparation stained for Myosin ATPase activity

histolgy muscle fibers light

slower/less stain

histolgy muscle fibers dark

faster/more stain

Various myosin isoforms in

muscle...some hydrolize ATP faster than others...

for histolgy have

fast-contracting muscles (white meat chicken breast

hydrolyze atp faster use

energy quicker then slow contracting)

staining for atphase activity

is why the diff between slowing contracting musles diff color less stain

fast twitch

white meat-fast contracting muscles using ATP quickly in histolgy so on a glass slide would appear darker

slow contracting muscles

would be lighter in histolgy because not using ATP as quickly

in terms of fast speedy explosive movements is

weight training is explosive but fatigue resistant

fast twitch

very low fatigue resistant but very high resistant of force (ex walk longer then weight lifting)

genetics

determine how much type 1 vs type 2 ex skinny armed is a runnner but sprinter is more beefy

say that we can change ratio 2a and 2b know muscles adapt and change

Type 1

slow twitch- very high fatigue resistance

is anarobic is oxygen depenedant slow oxidative

low force generation

high fatigue resistance

triglycerides fuel source

Type 2

: Fast twitch- break 2 into 2a and 2 b

type 2a

. is fast oxidative

fast twitch speed

medium fatigue resistance

fuel source glycogen

type 2b

fast glycolylic

very fast twitch speed

generation of force very high

fatigue resistance low

fuel source glycogen

motor units are made of

homogenous fiber types (the same motor units as one nerve activates same type)

-slow motor units produce

less force

-fiber are smaller

-fewer fiber

slow motor units are

received first

-allow range of control over motor tasks

mostly dependant on

velocity what makes fast/slow

Maximum shortening velocity (Vmax) is

different for different fiber types

three optimal muscle lengths

lower v max

slow muscles

higher vmax

fast muscle

Muscle fiber types can influence the

f-v relationship

Most muscles are a combination of

fast and slow fibers

The power curve for a single muscle can be

complex

Muscle

is Highly Adaptable

What adaptations does the system make response to the stimulus?

what we can change

can also change neural control (like bar workouts gain control in small units)

metabolic suppport (reflexted in vo2 max and heart rate)(adapt and become for efficent)

fiber type (2b and 2a vice verasa and 1 to 2)

what we can change

-muscle gets bigger what changes? the area (PCSA)

get more sarcometers in (series gives long but cross sectional area is more in parallelso

parallel)

also peak stress and peak force(stress=f/a)

can also change number of sarcomeres in series

Small # of intense contractions are most effective means of

Improving muscle size and strength

thinking about like weight lifting vs isometric )plank) versus quad

Maximum muscle enlargement requires

long term training 

(actual strength is long term training)

you can make muscles look big and not be strong

Fast fibers (Type II)

show the greatest hypertrophy (larger increases in cross-sectional area)

This is due to increased number and size of myofibrils

Also, there is an increase in the number of T-tubules and sarcoplasmic reticulum membranes

fiber effects

hyper (lots,high biggest)

so she largest increase in cross sectional area

see why weight lifters bigger in 2-3 weeks then a marathon runner can build fast twitch muscles but these muscles show th highest growth

Fiber Changes

Effects of strength training on cross-sectional areas of muscle fibers

Increase in the number of fibers (hyperplasia) is not observed in humans, but it is

observed in birds

Training Can

Affect Endurance

Trained muscles are

less fatigable

endurance-type 1

slow twitch fatigue resistance

as train these muscles get less fatigue

can get to the point of having endurance

Fibers in Athletes

Compare muscles in athletes & controls

are endurance athletes (long distance and cross country runner)

born with more type 1 fiber then nonathletes or do they develop?

nature and nurture 

Compare before and after training

found no significnt change from type 2 (fast twitch) to type one did see some change in 2b to 2a

found chronic simulation causes greater change (ex workout 3 times a week per semeter is better then wrkout for one week

consistency is key

Steroids

are derivatives of testosterone

Pharmacological steroids

are altered to increase half-life

Mechanism of action

Binds free androgen receptor

Translocated to nucleus

Alters expression of genes

Binds DNA

Binds DNA

increases protein production

reduces recovery time by limiting protein degradation

steroids

looking at anabolic effects : increases weight and fiber area

increase protein reduction and reduces recovery time so be in the gym for longer

works "best" in biological females and trained males

-females have lower testrones so females get gains wont ever had

-does not wrk well in untrained males (people who work out vs not work out)

just taking this wont make you beefier since the body already already testroceone

could end up with

live disfunction

infertility

Behavorial changes

Neuromuscular Injury and Disease

spinal cord injury

stroke,cerebral palsy,muscular dystrophy

Spasticity

Shorter optimal fiber length → stretched out

sarcomeres are

Higher passive force

Increased response to stretch

Differences in passive force-length properties

Differences in passive force-length properties

Changes in sarcomere proteins (titin)

Changes in stiffness of extra-cellular matrix

Spasticity

- abnormal muscle tightness and prolonged

muscle contraction

cerebal palsy

Effects of Chronic Stimulation

can also change

cardiovascular system

overall adpatation

Lieber stimulated rat muscle at 10 Hz & observed:

-3 hrs Swelling of the SR

4 days Increase size of mitochondria rise in oxidative enzyme activity rise in musicde blood flow

-14 days Increased Z-fine width and decrease Ca ATPase activity in SR

28 days Appearance of afow forms of actin and myosin; decrease in muscle bulk, avsociated with reduced fiber cross-sectional area

Chronic Stretch

in muscle will cause a change in fiber length

can also happen opposite way dont stretch/lack stretch cause issues

New sarcomeres are added when a

muscle is chronically stretched

Average sarcomere length is kept

relatively constant

Muscle Fiber Length (mm)

Bed rest and space travel affect muscles

similarly

Muscle wasting is

initially rapid

It is usually detectable by 3 days and then gradually slows

Atrophy depends on

previous muscle use

Hence, it is greatest for antigravity muscles leg. quads atrophy more than hams)

Physiology of Disuse

Disuse leads to atrophy, especially in slow twitch (Type 1) fibers, and some necrosis

Increase in endomysial and perimysial connective tissue

Muscles develop smaller twitch and tetanic tensions

Slower-twitch (IIa) fibers tend to change to faster-twitch (IIb)

Loss of motor drive such that MUs are not fully recruited

Reversible!