Lecture 7 - Exercising Muscles 2

Question 1

muscle fibre types

Answer 1

Type 1 (slow twitch)

• > makes up aroung 50% of fibres in an average muscle
• > peak tension in 110ms

Type 2 (fast twitch)

• > Type 2a: (around 25% in an average muscle)
• > type 2x (around 25% “ ”)
• > peak tension in 50 ms

Question 2

how does the speed of myosin ATPase vary in Type 1 and Type 2 muscle fibres

Answer 2

Fast myosin ATPase = fast contraction cycling/fast twitch fibres

Slow myosin ATPase = slower contraction cycling/slow twitch fibres

Question 3

how do we do a muscle biopsy

Answer 3

• > get a small (10-100g) piece of muscle is removed
• > it is then frozen, sliced, and examined under a microscope

Question 4

what doe gel electrophoresis do

Answer 4

separates different types of myosin by size, which allows us to quantify the different type/ratio of fibres

• > type 1 vs 2 have different types of myosin

Question 5

Sarcoplasic reticulum of Type 1 vs type 2 fibres

Answer 5

type 2 have more developed a more highly developed SR

• > this results in faster Ca release (3-5 time faster muscle contraction)

Question 6

motor units of type 1 vs type 2 muscles

Answer 6

Type 1

• > smaller neurons (innervate <300 fibres)

Type 2

• > larger neurons (innervate >300 fibres)

Question 7

rate muscle fibres based on their peak power

Answer 7

Type 2x > type 2a > type 1

• > effects of different SR, motor units, ect.

- > regardless of fibre type, all muscle fibres reach peak power at around 20% peak force

Question 8

explain the distribution/ratio of type 1 and 2 fibres

Answer 8

• > each person has different ratios but overall follow similar trends

*arm and leg ratios can be similar in one person but an athlete will have more Type 1 than a power athlete

Question 9

soleus’s fibre ratio

Answer 9

• > mostly composed of type 1 fibres

Question 10

fibre type determinants

Answer 10

genetic factors

• > determines which alpha-motor neurons innervate which fibres

training factors

• > endurance vs strength training can induce small (10%) change in fibre types

aging

• > muscles lose type 2 motor units as we age

Question 11

type 1 fibres during exercise

Answer 11

they have high aerobic endurance and efficiently produce ATP from fat and carbs

• > can maintain exercise for prolonged periods
• > requires O2 for ATP production

Question 12

type 2 fibres during exercise

Answer 12

Type 2 (in general)

• > poor aerobic endurance, fatigue quickly
• > produce ATP anaerobically

Type 2a

• > more force, faster fatigue than type 1
• > short, high inten. endurance events

Type 2x

• > often used for everyday activities
• > short explosive sprints

Question 13

muscle fibre/motor unit recruitment (both mean the same thing)

Answer 13

Method for altering force production

• > Less force production: fewer/smaller motor units are recruited

More force pro: more or larger MU are recruited

• > type 1 motor units are smaller than type 2

Question 14

muscle fibre recruitment order

Answer 14

type 1 - > type 2a - > type 2x

Question 15

size principle and how it relates to the order of motor unit recruitment

Answer 15

Size principle

• > order of recruitment of motor units directly relates to the size of alpha motor neurons
• > we only recruit the minimum number of motor neurons that are needed to perform an action

*Type 1 (smallest) first, then 2a, then 2x

Question 16

type of muscle contractions

Answer 16

Static (isometric) contraction

• > muscle produces force but does not change in length
• > joint angle does not change
• > velocity = 0m/s

Dynamic contraction (2 types)

• > muscle produces force and changes in length
• > joint movement is produced

Question 17

types of dynamic contractions

Answer 17

Concentric contraction

• > muscle shortens while producing a force (flexion)

Eccentric

• > muscle lengthens while producing a force (extension)

Question 18

which type of motor unit produces more force

Answer 18

Type 2 MU - > more force

Type 1 MU - > less force

Question 19

Frequency of stimulation

Answer 19

Twitch

• > response from 1 electrical stimulus

Summation

• > response from multiple stimuli, increases each other since they haven’t reach resting potential

Tetanus

• > frequent stimuli than maintain a certain contractile activity

Question 20

The Length - Tension relationship

Answer 20

optimal sarcomere length = optimal overlap

too short/too stretched = little to no force develops