MIDTERM 2 Flashcards
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
force-velocity relationship
varies depending on direction of mvmnt
why does force change w velocity?
- inefficient coupling of cross bridges, leads to dec force production
- takes time for myosin to attach 10ms, faster mvmnt = dec force - fluid viscosity: causes viscous friction
- velocity inc = viscosity inc
- fluid’s resistance to stress/deformation
- friction = iinternal force the muscle must overcome
concentric and force-velocity
as velocity of shortening INC, force DEC
bcs of cross-bridge coupling (there are most when at rest, dec as move)
fluid viscosity inc as velocity inc
- direction of Fr opposes direction of velocity, therefore viscosity is opposing motion
eccentric and force-velocity
as velocity of elongating INC, force INC
cross-bridge: myosin forced back, bonds are stretched and causes ELASTIC ENERGY
viscosity: Fr opposes velocity, but Fr is in same direction as muscle so it moves w motion
Fr = C x v
C = viscosity coefficient
v = velocity
Fr = force created by resistive vicious dampening
concentric dampening effect
Fm = Fg - Fr
resultant force = force generated by muscle minus force from resistive viscosity
as force moves up, viscosity moves down
viscosity OPPOSES force of muscle (velocity aka motion)
eccentric dampening effect
Fm = Fg + Fr
bcs velocity moves down, viscosity moves UP with the force of the muscle
adds to the generated force
ground force reaction
ground pushes back with equal force, in opposite direction
reaction force provided by horizontal support surface
force formula
force = mass x acceleration
law of inertia
inertia: objects resist any change in motion state
objects will stay still until compelled to
momentum formula
p = m x v
p is in kg x m/s
law of acceleration
the change of motion is proportional to the force placed on it and the direction
force = mass x acceleration
law of action-reaction
there is always an OPPOSITE AND EQUAL REACTION to every action
gravity
9.91 m/s2
magnus effect
when you spin an object, it makes a pressure gradient that causes mvmnt to move from high to low pressure
causes curved path in baseball
force platforms
used to measure rxn forces X, Y, Z and their respective moments of force
limitations:
- conscious walking
- mounting i.e. cannot be moved, elevated
balance boards are cheaper alternative, less good but comparable
pressure sensors
shoe insoles, allows repeated axis measurements i.e. running
- generates electrical charge responding to stress
limitations:
- only Fz, vertical loading
- slipping
- if feet too hot, confuses reading
vertical jump graph - position
starts at 0, goes down as prepare to jump, up as jump, down with gravity
phases of vertical jump
- -ve acceleration
- ground rxn force less than body weight - +ve acceleration
- vertical force > body weight - flight phase
- gravity pulls back down
- ground rxn force is 0 bcs in flight - impact phase
- tells info on force and acceleration
vertical force analysis
- impact peak: initial spike, N
- active peaks: in N
- 2 for walking: initial contact and pushing off when 2nd foot is down
- 1 for running - rate of loading (N/s)
- force at impact time from contact to impact
- force/time
- greater force in running, why more injuries - normalized values
- removes mass from being a factor of force
- i.e. running active peak 2200N/850N = 2.59 BWs (bodyweights) - timing
- of peaks, foot contact, toe off, etc.
- just analyzing graph
joint reaction forces
when forces cross at a joint in x,y
sum of forces on a joint
only calculated for STATIC joints, means that horizontal, vertical forces and moments = 0
normal force
force b/w 2 surfaces in contact w e/o
acts PERPENDICULAR to the surface
friction formula
Ff = mu x N
N is normal force
pressure formula
p = f/A
a is area
measured in pascals, Pa
1 Pa = 1 N/m2
moment formula
M = F x d
