MIDTERM 2 Flashcards
(49 cards)
EMG uses
diagnose:
- muscle tingling
- numbness
- weakness cramping patterns
determine:
- nerve dysfunction
- neuromuscular junction issues
- muscle dysfunction
surface EMG
electrodes placed on skin
no muscle contact
disadvantages: oil, hair, etc.
mitch research
they normalize the stress-strain relationship
- allows comparison across tissue sizes (bcs diff siz ox tails will have diff resistance)
stress is how we normalize force to tissue size
subcutaneous EMG
under skin but over muscle
aka indwelling EMG
intramuscular EMG
b/w muscle cells
aka indwelling EMG
cons of indwelling EMG
invasive, painful
doesn’t represent whole muscle
how to apply EMG
2 electrodes for every muscle, in line of muscle fibres direction
measures electrical gradient as activity moves
1 other electrode is on ground location i.e. bone
voltage is calc b/w ground and muscle b/w electrodes
EMG amplitude
not directly tied to force produced i.e. more force not equal to higher amp
intrinsic factors:
- # active motor units, more = higher amp
- fibre composition i.e. fast twitch
- blood flow
- fibre diameter
- distance b.w fibres and electrodes (if leaner, less distance)
extrinsic factors:
- distance b/w electrodes, close = fast
- placement of electrodes
- skin preparation
- perspiration
- temperature
potential noise
noise: electrical activity that’s not from the muscle
- mvmnt of cables/electrodes: called motion artifact
- electrical noise i.e. lights, heart
- equip issues
- cross talk from other muscles
outcome measures - EMG timing
EMG determines muscle activation and control
threshold: must be reached to be activated…only look at activity w/in the threshold, bcs anything else is noise
outcome measure - relative muscle effort
you CANNOT measure force thru EMG
normalization: finding max voluntary contraction/MVC, and comparing to value recorded thru action
- see % MVC used
parallel fibres and EMG
parallel > pennate, because there’s greater shortening of the entire muscle
= larger ROM
pennate fibres and EMG
rotate around tendon, causing fibres to INCREASE (eccentric)
higher fibre/unit = more FORCE
greater the pennate angle, the LESS force is transferred
full wave rectification
generates absolute values only (only postitive)
see what looks like in book
filtering
removes noise i.e. power lines
has 3 choices:
- low pass: only low frequencies shown
- high pass: keeps high frequencies
- band pass: many singals pass
linear envelope: lets frequencies b/w 2 freqs pass i.e. stop pass stop
integration
used to calculate area under curve of the linear envelope
can continue entire contraction or reset at timed intervals
contractile vs noncontractile
contractile: parts that generate force i.e. actin, myosin
noncontractile: connective tissue i.e. epimysium, indirect force
passive vs active vs total force
passive force: AKA elastic energy… connective tissue, contirbutes when stretched
active force: from contractile units
total force: passive and active tgt
tension and cross-bridges
tension is directly related to numb of cross bridges
more bridges = more force generation
what happens if muscle too stretched
the cross bridges separate, myosin heads not connected to actin
not much tension can be generated bcs of the filaments being pulled apart
what happens is muscle too shortened
fewer cross bridges can connect bcs they OVERLAP with other cross bridges
resting length
partially contracted state
when is there most force produced?
when the muscle is partially elongated
active force + some passive
when is active force decreased?
- when muscle too shortened
- when muscle too elongates
active force max at resting
