2. EMG and Muscle Physiology Flashcards
Electromyography
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
Hand Dynamometry
Test measuring pure motor ability
Strength of Preferred (dominant) Hand
5-10% stronger than non preferred hand
Strength
Capacity for gross muscular effort
Power
Effort at high speed
Electromyograph
Differences in amplitude of EMG recording reflects differences in number and size of active motor units
Number of Motor Units
Brain uses sensory receptors in muscles and tendons to determine
Isometric Contraction
Muscle is activated and held at constant length
Graded Response
Increased amplitude resulting from recruiting additional motor units
Tonus
Small amount of electrical activity between major pulses
Size Principle
Motor units will be recruited in order of size (smallest to largest) depending on intensity
Max Grip Strength (demographic differences)
Gender -size of muscle fibers -testosterone Age Height/weight
When holding an object does the number of motor units remain the same?
Yes
Are the same motor units used for the duration of holding that object?
No, different motor units are used in order to delay fatigue in specific motor units
Fast Twitch (aka Type II (glycolytic)) Fibers
Activated with max clench
Rapid fatigue
Energy source: glycogen
Slow Twitch (aka Type I (oxidative)) Fibers
Activated with moderate clench
Slow fatigue
Energy source: aerobic respiration
Fibers of any one motor unit are always…
of one type
Slow Oxidative
Red muscle (lots of myoglobin)
Type I
Slow twitch
Oxidative (lots of mitochondria)
Well supplied with capillaries
Fast Glycolytic
White
Type IIx (IIb)
Fast twitch
Anaerobic
Dependent on glycolysis
Larger in diameter than SO
High glycogen content
Fast Oxidative Glycolytic
Type IIa
Not abundant in humans
Fast twitch
Differentiation of Skeletal Muscle Fibers
Differentiated on basis of structural, contractile, biochemical properties
Speed of Contraction
Dependent on rate of ATP usage by myosin
Causes of Muscle Fatigue
- Reduced Ach
- Poor ATP supply
- Decrease in pH
- Accumulation of extracellular K
- Accumulation of lactic acid
- Decrease in glycogen
- Dehydration
- Hypoglycemia
Integrated EMG
Activity level of muscle (overall muscle effort)
Linear relationship between force produced by muscle and amount of iEMG
Non Exercise vs Exercise (1)
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)
Non Exercise vs Exercise (2)
CNS, neural adaptation, motor learning
Better synchronization of motor unit activation (use less force to produce a movement)
3 Sources of ATP
Creatine phosphate
Glycogen
Cellular respiration
Creatine Phosphate
Donates phosphate to make ATP
Fast but doesn’t last long (2-7 seconds)
Glycogen
Limited source
Comes from glucose stored in muscle and liver
Important under anaerobic conditions
2 ATP
Cellular Respiration
Required for prolonged activity
Lots of mitochondria
36 ATP
Slow Twitch Fibers (Type 1)
Red (lots of myoglobin)
Small fiber size
Small force
Slow contraction speed
High oxidative capacity
Fatigue resistant
Usage: posture, endurance
Fast Fatigable (Type IIB)
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
Fast Fatigue Resistant (Type IIA)
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
Motor Unit
Motor neuron and all the muscle fibers it innervates
One motor neuron per muscle fiber
Many muscle fibers per motor neuron
All muscle fibers innervated by a given motor unit will be…
Of the same type
Recruitment
Progressive activation of additional motor units
Order of Recruitment
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
More units activated…
Greater force of muscle contraction
All or None Phenomenon
Neuronal AP induces all the fibers of the motor unit to contract simultaneously
