Lecture 2

Question 1

what is torque

Answer 1

a measure of the force that can cause an object to rotate about an axis

Question 2

what are the role of satellite cells

Answer 2

make more nuclei and help cell repair

Question 3

explain the process of excitation contraction coupling = force generation

Answer 3

• nerve impulse travels down T tubules and causes release of Ca2+ from SR
• Ca2+ binds to troponin and causes position chnage in tropomyosin, exposing active sites on actin
• actin and myosin bind and contraction occurs
• ATP binding to myosin head, weakens its bind to actin so actin is released

Question 4

what happens at the neuromuscular junction to cause a contraction

Answer 4

• action potentials arrive at each nerve at neuromuscular junction
• depolarisation of motor end plate (excitation) is required to initiate contraction

Question 5

what happens to the muscle fibres is a motor neuron is stimulated

Answer 5

all fibres in that motor unit will contact synchronously

“all or none”

Question 6

what is the size principle in terms of motor neurons and which is activated first

Answer 6

motor neurons are recruited progressively by axon size, small to large

smaller axons reach their threshold first and are therefore activated first

Question 7

which type of muscle fibre is activated first and why is that

Answer 7

Slow twitch (Type I) muscle fibres are activated first

they have a lower threshold as they are smaller so are used first

Question 8

what are the two major benefits to the size principle

Answer 8

1. use fatigue resistant units longer
2. finer regulation with low force

Question 9

what does an increase stimuli (action potenital) initially do to muscle

Answer 9

increased frequency gives big increase force initially (summation)

Question 10

what does further increase in frequency of stimuli (action potential) do to muscle after summation

Answer 10

further increase in frequency will have a diminishing effect until tetanus

Question 11

what type of muscle fibre will always be used (low and also intense exercise

Answer 11

Type 1 = slow twitch

Question 12

what type (s) of muscle fibre is mostly used during intense exercise

Answer 12

Type IIa and also Type IIx

more Type IIx

Question 13

what is fatigue during exercise simply described as

Answer 13

reduction in strength

Question 14

what are the peripheral fatigue mechanisms

Answer 14

force is inhibited before either ATP of glyocgen can become depleted

Question 15

what is the optimal length tension relationship and why is it important

Answer 15

where the overlap between actin and myosin is best, allows for the most optimal force production

Question 16

fibre length to muscle length is also important when generating force

give examples of the hamstrings and quads and how they differ

Answer 16

hamstrings :
- longer fibre/muscle, less cross sectional area
- gives rapid shortening
- more risk of tear

quads :
- shorter fibre / muscle, more cross sectional area
- gives greater force capacity

Question 17

what is meant by “rate constraints” in terms of actin and myosin

Answer 17

cross bridges between actin and myosin attach / detach at certain rates

Question 18

as velocity increases what happens to the number of cross bridges formed and force generated

Answer 18

as velocity increases the number of cross bridges decreases and less force is generated

Question 19

muscles act around joints which means the force produced by a muscle is measure as …..

Answer 19

torque
- force at a particular distance from a joint axis, in Newton-meters, Nm

Question 20

power athletes will generate more torque at all velocities compared to endurance athletes ….. TRUE / FALSE

also what will happen to force as it drops

Answer 20

TRUE

force will drop at similar rates (in relative terms)

Question 21

if velocity is low what is an important force modulator

Answer 21

if velocity is low, length is an important force modulator

Question 22

at eccentric velocities what is the determinant of force

Answer 22

muscle velocity dominates length as the determinant of force at eccentric velocities

Question 23

what is the equation of power

Answer 23

work / time

Question 24

what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type 1 fibres

Answer 24

contraction time = slow

motor neuron size = small

fatigue resistance = high

useful duration = hours

force production = low

mitochondrial density = high

Question 25

what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type IIa fibres

Answer 25

contraction time = moderately fast

motor neuron size = medium

fatigue resistance = fairly high

useful duration = <30 mins

force production = medium

mitochondrial density = high

Question 26

what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type IIx fibres

Answer 26

contraction time = fast

motor neuron size = large

fatigue resistance = intermediate

useful duration = <5 mins

force production = high

mitochondrial density = medium

Question 27

what is the contraction time, motor neuron size, fatigue resistance, useful duration, force production and mitochondrial density of Type IIb fibres

Answer 27

contraction time = very fast

motor neuron size = vary large

fatigue resistance = low

useful duration = <1 min

force production = very high

mitochondrial density = low

Question 28

what are the reasons that muscle loss occurs with aging

Answer 28

• loss of growth related hormones
• loss of IGF-1 (causes increased protein production and decreased breakdown)
• also sarcopenia (active loss of muscle)
• accumulate fate and denervated fibres in muscles