5L skeletal muscles and adaptiation to exercise training

Question 1

What is skeletal muscle?

Answer 1

40-50% of total body mass
major site of metabolic activity
largest protein reservoir

Question 2

What are the 3 main functions of skeletal muscle?

Answer 2

1) locomotor activity
2) postural behaviour
3) breathing
4) other

Question 3

What is the structure of skeletal muscle?

Answer 3

muscle consists a number of muscle fibres lying parallel to one another and held together by CT

Question 4

What is a muscle fibre? (myofibre)

Answer 4

a single skeletal muscle cell
multinucleated
large, elongated, and cylindrically shaped
fibres can extend entire length of muscles

Question 5

What is myofibril?

Answer 5

• contractile elements of muscle fibre
  regular arrangement of thick and thin filaments (myosin and actin)
• alternating dark (the A bands) and light bands (I bands) giving appearance of striations

Question 6

What is the difference between a myofibre and myofibril?

Answer 6

Myofibers are the muscle cells itself.

Myofibrils are long protein cords in the sarcoplasm

Question 7

NWhat is a nerve?

Answer 7

a enclosed cable-like bundle of nerve fibres or axons

provides a common pathway for the electrochemical nerve impulses transmitted along each fo the axons

Question 8

What is the strength of contraction determined by?

Answer 8

number of fibre stimulated

frequency of stimulation

Question 9

what is a motor unit?

Answer 9

a motor neuron (nerve cell) and all of the fibres that it innervates
all fibres are of the SAME fibre type
group of fibres activated via the same neuron
all muscle fibres of one particular motor unit are always the Same fibre type

Question 10

precise (fine) movements

Answer 10

consists of a large number of motor units and few muscle fibres

Question 11

less precise movements (gross)

Answer 11

carried out by muscles composed of fewer motor units with many fibres per unit

Question 12

What is intra-muscle cooordination?

Answer 12

how much do you need?
mainly highly trained power athletes are able to activate up to 85% of their available muscle fibres simultaneously
(untrained)
trained athletes have not only a large = muscle mass than untrained individuals, but can also exploit a large number of muscle fibres
trained individuals can further increase strength only by increasing muscle diameter

Question 13

What is summation?

Answer 13

two successive ap if the twitch tension resulting form the first AP does not declines to zero before second twitch arrives, the twitch forces summate

Question 14

What is tetanus?

Answer 14

a frequncy of APs - a rise in the contractile force of a single muscle (fibre) until force reaches a plateau called the tetanic tension. This is the maximum tension that can be produced by a fibre.

Question 15

Slow twitch Fibres

Answer 15

swuited for repeated contractiosn durign activities requireing a force output of < 20-25% of max force output
- smaller motor units
first activated
examples: lower power activities, endurance events

Question 16

Muscle fibres Type:

the greater the slow twitch fibre content of a muscle…

Answer 16

the lower the force producing capactiy
the slower the contraction speed
the greater the endurance characteristics of the muscle
*based on typical size

Question 17

Fast twitch fibres

Answer 17

significant greater “force” and speed generating capability than slow twitch fibres (size and speed)
well suited for activities involved high power
activated after ST
larger motor units

Question 18

Muscle Fibre type:

the greater the fast twitch fibre content of a muscle..

Answer 18

1) greater the force output capacity
2) the greater the overall speed of contraction
3) the greater the fatigability will be when the muscle has been maximally activated
* based on typical size

Question 19

Properties of type 1 muscle fibres

Answer 19

red
slow oxidative (SO)
type I myosin
contractile: slow

Question 20

properities of type 2B

Answer 20

White
fast glycolytic
fastest contractile

Question 21

structural aspects of SO

Answer 21

muscle fibre diameter: dmall
mito density: High
capillary density: high
myoglibin content: high

Question 22

structural aspects of FG

Answer 22

Muscle fibre diameter: large
mito density: low
capillary density: low
myglobin content: low

Question 23

functional aspects of SO

Answer 23

twitch time: slow
relaxation time: slow
force production: low
fatigability: resistant

Question 24

Functional aspects of FG

Answer 24

twitch time: fast
relaxation time: fast
force production: high
fatigability: most fatigable

Question 25

metabolic aspects of SO

Answer 25

``` pc stores: low glycogen stores: low TG stores: high myosin ATPase activity: low glycolytic enzyme activity: low oxidative enzyme activity: high ```

Question 26

metabolic aspects of FG

Answer 26

``` pc stores: high glycogen stores: high TG stores: low myosin ATPase activity: high glycolytic enzyme activity: high oxidative enzyme activity: low ```

Question 27

Testosterone

Answer 27

directly effects muscle growth by binding to receptors on the surface of muscle cells and amplifying the biochemical signals in muscle tissue that result in protein synthesis. overall increase in muscular size, strength and recovery from exercise. more muscle but does not change the fibre type

Question 28

thyroid hormone

Answer 28

key hormoen wrt fibre type | increases mitos; mosin heavy change switch (type one decresases type 2 increases

Question 29

hyperthyroid

Answer 29

atrophy and muscle weakness

Question 30

can exercise training change muscles fibre types in humans?

Answer 30

it depends upon how one defines fibre types

Question 31

increased neuromuscular activity/overloadinging

Answer 31

endurance exercise repeated stimulation stretch move from fast to slow easier

Question 32

decrease neuromuscular activity, unloading

Answer 32

detraining, immobilization, microgravity harder to do but more inconveniences moving from slow to fast

Question 33

What is muscular strength?

Answer 33

the ability of a muscle or muclr group to exert focrce against a resitance commonly measured as a maximal value force and strength are synonymous

Question 34

factors influencing the force of muscle contractions:

Answer 34

1. the individuals state of health 2. the individuals training status 3. joint angles 4. muscle cross-sectional area 5. speed of movement (myosin heavy chain composition) 6. muscle fibre type (influences forces) 7. age 8. sex

Question 35

Force-velocity curve

Answer 35

at any given velocity the trained can apply more forces | against any given load the trained can move (an object) faster

Question 36

How do we get stronger?

Answer 36

myostatin, alpha actinin3 neural - motor unit recruitment hypertrophy - PS pathways, testosterone, IGH - 1 insulin

Question 37

Genes that define "skeletal muscle phenotype"

Answer 37

include: AMPK Calcineurin Peroxisome proliferator - activated receptor gamma (PPAR gamma) coactivator 1 alpha(PGC-1alpha)

Question 38

Type of contractions

Answer 38

in response to physiological demands, intracellular calcium concentration is elevated, activating calcineurin/nuclear factor of activated T cells (NFAT_ and MEF2/HDAC signaling pathways. In response to workload, ATP is depleted activated AMPK

Question 39

AMPK

Answer 39

sustained depression of energy change [atp] decrease < -- > {ADP] increase [AMP] increases --> AMPK --> mitochondiral biogensesis, Glut 4, HK (increased oxidative metabolism, not MHC) has many roles

Question 40

Calcineurin

Answer 40

a ca2+/calmodulin activate phosphatase - implicated in enrve activity - dependent fibre type specification in skeletal muscle controls the phopshyrlation state of transcription factor NFAT alow for its translocation to the nucelus - leading to the activation of slow type msucle proteins in cooperation with myocyte enhancer factor 2 (MEF2) causes a change from fast to slow muscles

Question 41

PGC -1 aplha

Answer 41

transcriptional co-activator PGC-1 alpha drives the formation of slow-twitch muscle fibres regulates the genes involved in energy metabolism regulator of mitochondrial biogenesis and function activated in endurance exercise in human skeletal muschle major factor that regulated muscle fibre type determination serves as a target for calcineurin singling

Question 42

PGC-1alpha + nuclear receptor PPAR-gamma

Answer 42

permits the interaction of this protein with multiple trnasciption factors

Question 43

Neural response

Answer 43

the first measurable effect is an increase in the neural drive stimulating muscle contraction. within just a few days, an untrained individual can achieve measurable strength gains (without hypertrophy) resulting from learning to use the muscle

Question 44

increased strength with NO hypertrophy

Answer 44

development of maximal strength through increased intra-muscular coordination (the abiltiy to recruit more motor units)

Question 45

Hypertrophy

Answer 45

is the increase of the size of an organ or in a select area of the tissue

Question 46

how you get bigger = rate of protein synthesis vs. rate of protein degradation MPS = muscle protein synthesis factional synthetic rate protein accretion

Answer 46

PS = PD = Mass PS > PD increase mass increase PS = increase mass decrease degration = increase mass

Question 47

hormonal responses

Answer 47

controls myofibre size and maturation by idnirect and direct actions does not directly affect the proliferation and differentiation of hte cells that make the muscle in the first place testoersterone insulin growth hormone (IGF-1)

Question 48

insulin and myofibres

Answer 48

myofibres have more insulin receptors tahn type 1 IGF receptors, thus insulin is nexessary for myofiber hypertrophy. (nexessary to store protein in muscle)

Question 49

resting muscle and insulin

Answer 49

the resting muscle needs insulin to increase in size, thus following a meal, when insulin is secreted, excess nutrients can be stored in muscle. If insulin is low, protein stores are mobilized (protein degradation increases)

Question 50

myofibres and contracting muscle

Answer 50

contracting msucles DO NOT need insulin for glucose uptake; thus nutrietns in the cirulation can enter muscle to supply energy for contraction without eating a meal and getting the subsequent rise in circuatling insulin

Question 51

insulin

Answer 51

eating keeps insulin high and therefore keeps protein synthesis high

Question 52

insulin and GH

Answer 52

in response to IGF, the AKt/mTOR signalling pathway is activated. Activation of mTOR by AKT promotes protein synthesis and increases muscle mass --> hypertrophy Foxo is an inhibiting pathway

Question 53

hypertophy (presynthetic/anabolic) pathways

Answer 53

GH - IGF signalling AKT - mTOR pathway P13k - Akt-GSK3beta pathway ca2+

Question 54

Growth hormone (IGF-1)

Answer 54

stimualtes igf-1 gorwht factor with a configuration which closely resembles insulin --> increase protein synthesis produced in the liver and skeletal muscles by GH many of the actions fo the GH are through IGF-1

Question 55

p70s6 kinase

Answer 55

targets s6 ribosomal protein --> phosphoraltyion --> protein synthesis in the ribosome --> increase type II area after training

Question 56

training for strength

Answer 56

low reps with high loads

Question 57

training for endurance

Answer 57

high reps low loads

Question 58

repeated muscle contraction

Answer 58

PGC-1 activates that does not activate fox O therefore causes protein degration inhibition and then pgf also icnrease slow fibres in the mito --> aerobic cpaacity increases local IGF-2 inhibits fox O and activates AKT--> MTOR which increase protein synthess _->icnrease fibre size

Question 59

Satelitte cells

Answer 59

a distinct sub-population of myoblasts that fail to differentiate and remain associated with the surface of the developing fibre as quiescent "muscle cells" are precursors to primary myoblasts muscle stem cells surrounded by basal lamina join existing fibre or replace a damged cell

Question 60

types of muscle contraction: static | isometic strength training

Answer 60

limitations: - strengethens muscle at a specific pt in ROm time consuming

Question 61

Tpyes of muscle contraction: dynamic | plyometric training

Answer 61

uses explosive humps to mobilize the stretch-recoil properties of msucle ballistic resistance

Question 62

Muscle soreness and stiffness

Answer 62

delyed onset msucel soresness (DOMS) | lengthening contractiosn produce muscle soreness

Question 63

hyperplasia

Answer 63

increase the nubmers of cells

Question 64

Hyperplasia or hypertrophy

Answer 64

mostly hypertrophy

Question 65

physiological effects of strength training

Answer 65

increased muscle mass and size of muscle fibres increased utilization and coordination of motor units incrased strength of tendons, ligaments and bones increased storage of fuel in and blood supply to muscles improvmenets in blood - fat levels and biochemical processes.