Exam 3 Skeletal Muscle Adaptations

Question 1

Muscle fibers recruited first

Answer 1

In general, during any muscular activity, slow fibers are recruited first
Requirement for stronger contractions results in recruitment of fast fibers

Question 2

Clinical Correlation of recruitment order of muscle fibers

Answer 2

Repetitive, low-intensity exercise recruits predominately slow twitch fibers (type I)

Rapid power movements (or strong isometric contractions) recruit all three fiber types (Type I, Type IIa, and Type IIb)

Question 3

Motorneurons to type I fibers

Answer 3

Are smaller and innervate 100-180 muscle fibers

Question 4

Motorneurons to type II fibers

Answer 4

are larger and innervate 300-800 muscle fibers

Question 5

Type I and Type II fibers individually create very _____ amounts of force

Answer 5

similar

Question 6

The main difference in force development between types is

Answer 6

motor unit size (and muscle fiber twitch velocity)

Question 7

Why are motor units recruited such that only 1/3-1/2 of muscle fibers are contracting at one time?

Answer 7

This prevents injury that could occur if all fibers contracted at once

Question 8

Muscle fatigue

Answer 8

Inability of contractile and metabolic processes of muscle fibers to continue supplying the same work output; usually the result of repetitive stimulation

Question 9

Fatigue of muscle is based on

Answer 9

its maximal force output

Any decrement in maximal force is considered fatigue

Question 10

what generates fatigue?

Answer 10

Any reaction in the sequence from motorneuron AP generation to force generation by actin and myosin could be impaired to generate fatigue

Question 11

Muscle fatigue is associated with that factors

Answer 11

Depletion of muscle ATP, glycogen, and creatine phosphate
Delivery of nutrients and oxygen by the cardiovascular system
Decrease in motorneuron activity (AP signaling)
Build up of lactic acid (H+ ions) - reduces fiber pH from 7.0-6.0 (in fast twitch), lower pH inhibits the metabolic mechanisms of muscle fiber contraction

Question 12

Cause of fatigue in muscle fibers

Answer 12

depletion of ATP; rate of ATP utilization is greater than the rate of ATP formation (via glycolysis, oxidative phosphorylation, creatine phosphate)

Question 13

What is utilized at initiation of contraction

Answer 13

ATP
increased concentration of ADP + Pi stimulate glycolysis and oxidative phosphorylation; creatine phosphate maintains ATP production while glycolysis and oxidative phosphorylation produce “new” ATP

Question 14

At Moderate exercise rates ATP can be supplied by

Answer 14

Oxidative phosphorylation

Question 15

Why does glycolysis augment ATP production during intense exercise rates?

Answer 15

Delivery of oxygen by the circulation is overwhelmed; oxidative phosphorylation cannot produce ATP fast enough
(Glycolysis produces ATPs very quickly, but is an inefficient use of stored glycogen - 2 ATP vs 38 ATP)

Question 16

In regards to muscle fatigue and recovery, after intense exercise

Answer 16

creatine phosphate is depleted, glycogen is depleted, both must be newly synthesized to return muscle to normal state

Question 17

Why does increased pulmonary respiration continue for some time after intense exercise

Answer 17

to provide ATPs necessary for synthesis of glycogen and creatine phosphate

Question 18

20-45% of actual energy used during muscle activity is utilized for contraction, what happens to the rest of it?

Answer 18

the majority of the energy is lost as heat

Question 19

muscle adaptations occur throughout life in response to

Answer 19

work demands

Question 20

muscle is affected by

Answer 20

frequency, duration and intensity of work demands

Question 21

Remodeling of muscles consists of alterations in muscle characteristics:

Answer 21

fiber diameter, fiber length, vascular supply, fiber type, and sometimes fiber number

Question 22

Observable adaptations can occur in

Answer 22

as little as 2 weeks of training or disuse

Question 23

Hypertrophy

Answer 23

increase in size of muscle due to increase in the size of cells (increase of myofibrils)

Question 24

Atrophy

Answer 24

Decrease in size of muscle due to decrease in the size of cells (loss of myofibrils)

Question 25

Hyperplasia

Answer 25

increase int he size of a tissue due to increase in number of cells; believed to be due to fiber splitting

Question 26

Fiber transformation

Answer 26

alteration in muscle fiber type due to work demand (change in muscle metabolic capabilities - i.e. glycolytic to oxidative)

Question 27

Immobility (casting, bed rest, microgravity) imposes load restrictions of muscle that result in

Answer 27

atrophy of unused muscle tissue loss of muscle mass, strength, and endurance increase in fat content of muscles reduction in diameter of muscle fibers reduction in contractile proteins of muscle (decrease synthesis and increased degradation)

Question 28

Effects of disuse atrophy

Answer 28

- reduced oxidative enzymes decreases muscle endurance (disuse has minimal effect on the glycolytic process, fast twitch fibers are less affected by disuse atrophy) - Depletion of glycogen and creatine phosphate stores in muscle fibers - Disuse atrophy is reversible (longer period of disuse requires a longer recovery period; muscle fibers that are not innervated do not typically recover from disuse atrophy - e.g. nerve damage, SCI)

Question 29

Type of fibers most affected by disuse atrophy

Answer 29

Slow twitch fibers

Question 30

Can lose 50% ______ in 6-8 weeks with complete disuse

Answer 30

muscle mass

Question 31

Can lose 50% _____ in 3-5 weeks of disuse

Answer 31

strength

Question 32

Prolonged disuse (2 or more years) results in

Answer 32

Non-functional muscle with fibers replaced by collagen and fatty tissue (typical in complete nerve transection or spinal cord injury)

Question 33

Disuse atrophy: denervation

Answer 33

loss of neural connection to muscle induces atrophy and fibrosis of muscle (trophic factor(s) from neuron to muscle fiber have been lost; more rapid decline in muscle atrophy with denervation compared to disuse atrophy, can result in muscle with 5-10% its original volume)

Question 34

Denervation > 1-2 years renders muscles

Answer 34

completely non-function

Question 35

denervated muscles/fibers are composed of

Answer 35

fat, fibrous tissue with few, if any, contractile proteins

Question 36

immobilization preferentially affects

Answer 36

type I fibers i.e. - muscles typically lose their endurance (fatigue resistant) much more rapidly than their strength (fatigue-able)

Question 37

Following immobilization , type I fibers shoe

Answer 37

greater reduction of contractile function compared to type II fibers

Question 38

For elite athletes, immobilization affects the

Answer 38

fiber type affected by the chose sport; i.e. sprinter -> type II fibers affected first

Question 39

Prevention of atrophy

Answer 39

atrophy can be prevented with early motion (AROM) | Electrical stimulation following immobilization can prevent type I atrophy and loss of oxidative capacity

Question 40

Contracture

Answer 40

restricted ROM across a joint

Question 41

Contractures are related to

Answer 41

shortening of muscle and periarticulare joint structures (connective tissue of joints)

Question 42

How does muscle shorten

Answer 42

by removal of terminal sarcomeres in fibers; occurs when muscles are held in shortened positions for prolonged periods (weeks to months)

Question 43

Significant disabilities associated with contractures include

Answer 43

ADLs, transfers, ambulation, endurance

Question 44

Muscle hypertrophy

Answer 44

increased use (training) of muscle fibers results in hypertrophy of those fibers A few strong (maximal) contractions per day creates hypertrophy in 6-10 weeks Increased number of myofibrils (increased muscle diameter)

Question 45

Anaerobic training induces

Answer 45

- increased protein synthesis (actin and myosin filaments) - Increases glycolytic and aerobic enzyme machinery - increased glycogen, creatine, ATP content of fibers

Question 46

Connective tissue elements of muscle fibers also are increased via what process

Answer 46

collagen production by fibroblasts

Question 47

CT elements hypertrophy allows for

Answer 47

increase in size/strength of tendons and ligaments

Question 48

fiber-specific training

Answer 48

fibers trained are those that will hypertrophy | order of fiber recruitment has a role in fiber hypertrophy

Question 49

order of fiber recruitment

Answer 49

slow (type I) > Fast (type IIa) > fast (type IIb)

Question 50

Strength training

Answer 50

short duration, high resistance exercise creates increases in muscle mass and strength

Question 51

Hypertrophy is greatest in strength training when

Answer 51

muscle operates at or near maximum force-generating capacity (4-6 reps at near max force in sets of 3)

Question 52

Strength training results in increases of

Answer 52

actin and myosin proteins SR and T-tubule systems glycogen, glycolytic enzymes, creatine, and ATP

Question 53

Aerobic training

Answer 53

low intensity, long duration training results in enhancement of fiber fatigue-resistance

Question 54

aerobic training results in increases of

Answer 54

- number of mitochondria and mitochondrial enzymes - amount of fat sores and enzyme for their metabolism - increase in capillary network and blood flow (to deliver oxygen and remove metabolites)

Question 55

Aerobic training also creates enhanced

Answer 55

respiratory and circulatory systems | improved/increase oxygen and fuel delivery- e.g. more efficient pulmonary ventilation and delivery of oxygenated blood

Question 56

Overall, minimal actual hypertrophy occurs in __________ with aerobic training

Answer 56

slow twitch fibers The small amount of slow twitch fiber hypertrophy is balanced by fast fiber atrophy = minimal net gain in muscle size or power

Question 57

Fiber transformation

Answer 57

Change in fiber type classification due to training activities (e.g. heavy endurance training can transform type II fibers (fast) into slow twitch type I fibers)

Question 58

Scientific evidence exists for fiber transformation following intense, prolonged training suggesting:

Answer 58

that aerobic (endurance) training leads to conversion of type IIb to IIa and type IIa to type I fibers resistive exercise does not appear to transform fibers from slow to fast types

Question 59

Fiber transformation accounts for _______ of overall muscular adaptations to training

Answer 59

very little

Question 60

most alterations due to training are

Answer 60

fiber specific

Question 61

hypertrophy of type II fibers =

Answer 61

increased force generation

Question 62

increased fatigue resistance to type I fibers =

Answer 62

increased muscular endurance

Question 63

For endurance and power athletes, the high proportion of slow twitch fibers and fast twitch fibers, respectively, is believed to be

Answer 63

inherited (not trained)