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84 Cards in this Set

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What is the purpose of muscle mechanical function?
1. develop force and power
2. dissipate mechanical energy (stretch of tendon etc. stores energy)
3. force-length-velocity property (stabilize movement until reflexes become active)
4. redistribute mechanical energy between segments
Factors that affect muscle strength:
fiber type
age
gender
anthropometry (size, length, insertion, etc.)
physiologic cross section
pennation angle
length tension ratio
psychological factors
fatigue
Type 1 muscle
slow twitch
aerobic- oxidative
fatigue resistant
type 2 muscle
fast twitch
anaerobic- glycolytic
less fatigue resistant
subtypes of type 2 muscle
2A: glycolytic and oxidative

2B: glycolytic
physiological cross sectional area
-measure of the number of sarcomeres that are parallel with the angle of pull of the muscle
-PCA= (mass of fibers)/(density of muscle) x physiological length of muscle
-most muscles have a density of 1.056 g/cm3
pennation angle
-orientation of the fibers
usually an angle from the long axis of the muscle
-the angle increases as the muscle shortens
-the pennation angle affects the muscles ability to produce power by changing the PCA of the muscle
Length tension ratio
-muscles are strongest at their physiological length
concentric muscle contraction
-muscle length decreases when contracting
-acceleration
-gastrocnemius in terminal stance
eccentric muscle contraction
-muscle increases in length when contracting
-deceleration
-shock absorption
-soleus in midstance
isometric muscle contraction
-muscle length remains the same during contraction
-produces stability
-posture
-ex. hip abductors midstance
When is EMG activity the greatest: eccentric or concentric contraction?
concentric contraction
which type of contraction occurs during walking?
mostly isometric and eccentric
How does work change between level, ascent, and descent
level: 16J/step
descent: 18J/step
ascent: 32J/step
When does peak muscle activity of the gluteus maximus and adductor magnus occur?
Heel contact
What do EMG based studies miss?
1. don't address muscle coordination, synergy and transfer of energy between segments
2. don't address elastic storage of energy and later transfer in gait
What is a new way to study segmental accelerations and powers describing muscle synergy?
dynamical simulations
How does muscle coordination, synergy and energy transfer change with age?
increased antagonist co-activation is a possible adaptation to ensure joint stability with walking in older adults
Phase of gait with peak muscle activity of the adductor longus
heel contact
Phase of gait with peak muscle activity of the gluteus maximus
heel contact
Phase of gait with peak muscle activity of the quadriceps
loading response
Phase of gait with peak muscle activity of the Gastrocnemius, Soleus, PT, PL, PB, FDL, FHL
terminal stance
Phase of gait with peak muscle activity of the adductor longus and rectus femoris
preswing
Phase of gait with peak muscle activity of the sartorius, iliacus, gracilis, biceps femoris, AT, EHL, EDL
initial swing
Phase of gait with peak muscle activity of the biceps femoris, semitendinosis, semimembranosis, TA
terminal swing
What is the soleus's job in gait?
decelerate internal rotation and forward movement of the tibia during midstance

stabilize the lateral column

assist in plantarflexion during terminal stance
What is the role of the gastrocnemius
flex the knee during
What is the role of the extensor muscles of the leg?
eccentric contraction to resist plantarflexion during heel strike and loading response

dorsiflexion- peak activity in initial swing

EDL and EHL initiate pronation during preswing, initial swing, and midswing

the TA supinates the midtarsal long. axis during initial swing and midswing
what is the role of the hamstrings during gait
most active in terminal swing

resist excessive flexion of the knee
What happens when you apply a 4 degree forefoot varus/medial wedge to a normal foot?
the midtarsal joint has 3 possible positions: maximally pronated, supinated, or maximally supinated.

It is able to pronate/supinate 4-6 degrees.

Thus, the midtarsal joint can handle this alone
what happens when you apply a 10 degree varus/medial forefoot wedge to a normal foot?
The midtarsal joint can supinate 4-6 degrees. The remainder of the supination must be from the subtalar joint.
What happens when you apply a 4 degree valgus/lateral wedge to the forefoot (normal foot)?
The midtarsal joint is already fully pronated.

The subtalar joint pronates to compensate.

ankle: supinates

tibia: internally rotates

knee: flexes and internally rotates

hip: internally rotates
What happens when you apply a 10 degree valgus/lateral heel wedge to a normal foot?
the lateral forefoot is off the ground.

GRF are unequal at the heel.

over time the foot will sublux
What happens when you apply a 4 degree varus wedge to the rearfoot of a normal foot?
The midtarsal joint is already fully pronated.

Because the subtalar joint is supinated the 2 axes are more divergent and the ROM is decreased (elftman's theory). The forefoot will be inverted at least 4 degrees but maybe more.

subtalar joint: supinating
ankle: pronating
tibia: ext. rotating
knee: extending, externally rotating

will act as the longer side due to being supinated
What happens when you apply a 4 degree valgus wedge to the rearfoot of a normal foot?
midtarsal joint: supinate
subtalar joint: pronate
the forefoot will be inverted relative to the ground
ankle: supinates
tibia and femur: internally rotate
rearfoot deformity
position of the rearfoot relative to the floor when the subtalar joint is in neutral position (neutral calcaneal stance position)
total rearfoot deformity=
neutral calcaneal stance position

subtalar joint neutral position + tibial influence
neutral calcaneal stance position is the sum of:
subtalar joint neutral position + tibial influence
subtalar joint neutral position
the frontal plane relationship of the leg bisection to the calcaneal bisection while the subtalar joint is in neutral position
tibial influence
the frontal plane relationship of the tibia to the ground while the subtalar joint is in neutral position
What kind of deformities affect tibial influence?
Frontal plane deformities like:
genu varum/valgum
tibial varum/valgum
How do you calculate rearfoot deformity?
tibial influence + Subtalar joint neutral position
rearfoot varus
the rearfoot is inverted with respect to the ground when in neutral calcaneal stance position
What are the 2 possible components of rearfoot varus?
subtalar joint varus and/or varus tibial influence
What are some causes of subtalar joint varus?
calcaneal varus:
-medial hypoplasia of the calcaneus
-lack of normal ontogeny
Talar varus
-medial hypoplasia of talus
varus orientation of joint itself
inverted tibial plafond (not a true STJ varus but will appear as an inverted calcaneal bisection)
tibial varum
bowing of the lower 1/3 of leg (inadequate ontogenous change)

pathophysiological bowing (rickets,etc)

hypoplasia of medial tibial epiphysis
compensation
the way the body responds to a deformity or abnormal function
compensated or fully compensated
GRF are equal across the STJ axis/plantar aspect of the heel/plantar aspect of the foot
partially compensated
GRF cannot be equalized because a fully compensated position is unable to be reached
uncompensated
no motion has occurred to provide compensation
overcompensated
motion has occurred beyond what was required for full compensation
Where do we measure compensation?
relaxed calcaneal stance position
What are the 3 components of relaxed calcaneal stance position?
deformities in all 3 planes:
frontal plane deformities
sagittal " "
transverse " "
Give an example of a frontal plane deformity:
genu varum/valgum
give an example of a sagittal plane deformity:
equinus deformity
give an example of a transverse plane deformity:
metatarsus adductus
compensation for rearfoot varus:
GRF will be on lateral side of foot (lateral to subtalar joint axis).

The midtarsal joint will be maximally pronated (by definition) and unable to compensate.

subtalar joint pronation will occur until GRF are equal across the subtalar joint/plantar aspect of the heel/plantar aspect of the foot.

in an isolated rearfoot varus deformity, pronation at the subtalar joint generally occurs until the calcaneus is perpendicular or until end range of pronation whichever comes first
in order to figure out compensation (relaxed calcaneal stance position) for any forefoot and rearfoot deformities you must know or figure out:
1. STJ inversion and eversion
2. STJ neutral position
3. tibial influence
4. maximally pronated position
5. where fully compensated would be
How do you calculate subtalar joint neutral position?
(inversion + eversion)/3 -eversion
how do you calculate neutral calcaneal stance position?
tibial influence + Subtalar joint neutral position

aka total rearfoot deformity

position of the rearfoot relative to the floor when the subtalar joint is in neutral position
How do you calculate the point of maximal pronation of the rearfoot?
Tibial influence + subtalar joint eversion
subtalar joint neutral position
the frontal plane relationship of the leg bisection to the calcaneal bisection while the subtalar joint is in neutral position
tibial influence
the frontal plane relationship of the tibia to the ground while the subtalar joint is in neutral position

affected by frontal plane deformities: tibia varum/valgum, genu varum/valgum
rearfoot varus can be caused by what 2 things
varus tibial influence

subtalar joint varus
compensated or fully compensated
GRF are equal across
-the the STJ axis
-plantar aspect of the heel
-plantar aspect of the foot
partially compensated
at the end of range of motion, a fully compensated position is unable to be reached

GRF are unable to equalize
uncompensated
no motion has occurred to provide compensation
overcompensation
motion has occurred beyond what was required for full compensation
relaxed calcaneal stance position
STJ position as a result of compensation for deformities in all three planes.

frontal: genu varum/valgum
sagittal: equinus
transverse: metatarsus adductus
where will GRF be in a rearfoot varus deformity?
lateral to the subtalar joint axis
What will the midtarsal joint do to compensate for the rearfoot varus?
nothing, it is already maximally pronated
What will the subtalar joint do in rearfoot varus?
it will pronate until GRF is equal across
the subtalar joint
the plantar aspect of the heel
the plantar aspect of the foot
in a rearfoot varus deformity how far does the subtalar joint pronate
until the calcaneus is perpendicular or until the end range of pronation,

whichever comes first
maximally pronated position
Tibial influence + subtalar joint eversion
fully compensated rearfoot varus deformity
GRF are equal
medial and lateral to the STJ axis
across the plantar surface of the heel
across the plantar surface of the foot when the calcaneus reaches perpendicular provided there are no other deformities requiring compensation

in a fully compensated rearfoot varus deformity, RCSP=0
uncompensated rearfoot varus
NCSP= RCSP
rearfoot valgus
rearfoot is everted with respect to the ground when standing in NCSP
What is rearfoot valgus composed of?
subtalar joint valgus

valgus tibial influence

very rare
valgus tibial influence
genu valgum

tibial valgum
rearfoot valgus
GRF will be on the medial side of the foot medial to the MTJ and STJ axes providing an external supinatory movement
Where does compensation take place in rearfoot valgus?
longitudinal midtarsal joint axis which is able to supinate 4-6 degrees to compensate
What happens if rearfoot valgus is greater than 4-6 degrees
the subtalar joint may help the longitudinal midtarsal joint and also supinate
What happens to the forefoot when the longitudinal midtarsal joint supinates?
it makes the forefoot unstable

supination decreases the ROM available at the midtarsal joint
what happens to the subtalar joint when a deformity places the STJ in an everted position of greater than 5 degrees?
it is forced to go to the end range of pronation

forefoot supinatus is likely to develop