2. EMG and Muscle Physiology

Question 1

Electromyography

Answer 1

Measure of changes in electrical potential on the surface of the skin by muscle action potentials being conducted along nearby muscle fibers when a muscle contracts

Question 2

Hand Dynamometry

Answer 2

Test measuring pure motor ability

Question 3

Strength of Preferred (dominant) Hand

Answer 3

5-10% stronger than non preferred hand

Question 4

Strength

Answer 4

Capacity for gross muscular effort

Question 5

Power

Answer 5

Effort at high speed

Question 6

Electromyograph

Answer 6

Differences in amplitude of EMG recording reflects differences in number and size of active motor units

Question 7

Number of Motor Units

Answer 7

Brain uses sensory receptors in muscles and tendons to determine

Question 8

Isometric Contraction

Answer 8

Muscle is activated and held at constant length

Question 9

Graded Response

Answer 9

Increased amplitude resulting from recruiting additional motor units

Question 10

Tonus

Answer 10

Small amount of electrical activity between major pulses

Question 11

Size Principle

Answer 11

Motor units will be recruited in order of size (smallest to largest) depending on intensity

Question 12

Max Grip Strength (demographic differences)

Answer 12

Gender
-size of muscle fibers
-testosterone
Age
Height/weight

Question 13

When holding an object does the number of motor units remain the same?

Answer 13

Yes

Question 14

Are the same motor units used for the duration of holding that object?

Answer 14

No, different motor units are used in order to delay fatigue in specific motor units

Question 15

Fast Twitch (aka Type II (glycolytic)) Fibers

Answer 15

Activated with max clench

Rapid fatigue

Energy source: glycogen

Question 16

Slow Twitch (aka Type I (oxidative)) Fibers

Answer 16

Activated with moderate clench

Slow fatigue

Energy source: aerobic respiration

Question 17

Fibers of any one motor unit are always…

Answer 17

of one type

Question 18

Slow Oxidative

Answer 18

Red muscle (lots of myoglobin)

Type I

Slow twitch

Oxidative (lots of mitochondria)

Well supplied with capillaries

Question 19

Fast Glycolytic

Answer 19

White

Type IIx (IIb)

Fast twitch

Anaerobic

Dependent on glycolysis

Larger in diameter than SO

High glycogen content

Question 20

Fast Oxidative Glycolytic

Answer 20

Type IIa

Not abundant in humans

Fast twitch

Question 21

Differentiation of Skeletal Muscle Fibers

Answer 21

Differentiated on basis of structural, contractile, biochemical properties

Question 22

Speed of Contraction

Answer 22

Dependent on rate of ATP usage by myosin

Question 23

Causes of Muscle Fatigue

Answer 23

• Reduced Ach
• Poor ATP supply
• Decrease in pH
• Accumulation of extracellular K
• Accumulation of lactic acid
• Decrease in glycogen
• Dehydration
• Hypoglycemia

Question 24

Integrated EMG

Answer 24

Activity level of muscle (overall muscle effort)

Linear relationship between force produced by muscle and amount of iEMG

Question 25

Non Exercise vs Exercise (1)

Answer 25

After strength training: same amount of muscle force requires less iEMG (think of trained rowers) Non exercise: require more overall effort to perform work (think of untrained rowers)

Question 26

Non Exercise vs Exercise (2)

Answer 26

CNS, neural adaptation, motor learning Better synchronization of motor unit activation (use less force to produce a movement)

Question 27

3 Sources of ATP

Answer 27

Creatine phosphate Glycogen Cellular respiration

Question 28

Creatine Phosphate

Answer 28

Donates phosphate to make ATP Fast but doesn't last long (2-7 seconds)

Question 29

Glycogen

Answer 29

Limited source Comes from glucose stored in muscle and liver Important under anaerobic conditions 2 ATP

Question 30

Cellular Respiration

Answer 30

Required for prolonged activity Lots of mitochondria 36 ATP

Question 31

Slow Twitch Fibers (Type 1)

Answer 31

Red (lots of myoglobin) Small fiber size Small force Slow contraction speed High oxidative capacity Fatigue resistant Usage: posture, endurance

Question 32

Fast Fatigable (Type IIB)

Answer 32

White (not as much myoglobin) Large fiber size Large force Fast contraction speed Low oxidative capacity Easily fatigable Usage: gallop, jump, rapid movement Lots of power, strength

Question 33

Fast Fatigue Resistant (Type IIA)

Answer 33

White (not as much myoglobin) Large (not as much as IIB) Intermediate force Fast contraction speed Moderate to high oxidative capacity Fatigue resistant (less than I) Usage: run

Question 34

Motor Unit

Answer 34

Motor neuron and all the muscle fibers it innervates

Question 35

One motor neuron per muscle fiber

Answer 35

Many muscle fibers per motor neuron

Question 36

All muscle fibers innervated by a given motor unit will be...

Answer 36

Of the same type

Question 37

Recruitment

Answer 37

Progressive activation of additional motor units

Question 38

Order of Recruitment

Answer 38

Starting with smallest motor units, progressively larger unites are recruited with increasing strength of muscle contraction First: Smaller motor units (Type 1) I --> IIa --> IIb

Question 39

More units activated...

Answer 39

Greater force of muscle contraction

Question 40

All or None Phenomenon

Answer 40

Neuronal AP induces all the fibers of the motor unit to contract simultaneously