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84 Cards in this Set
- Front
- Back
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What is the purpose of muscle mechanical function?
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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 |
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Factors that affect muscle strength:
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fiber type
age gender anthropometry (size, length, insertion, etc.) physiologic cross section pennation angle length tension ratio psychological factors fatigue |
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Type 1 muscle
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slow twitch
aerobic- oxidative fatigue resistant |
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type 2 muscle
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fast twitch
anaerobic- glycolytic less fatigue resistant |
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subtypes of type 2 muscle
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2A: glycolytic and oxidative
2B: glycolytic |
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physiological cross sectional area
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-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 |
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pennation angle
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-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 |
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Length tension ratio
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-muscles are strongest at their physiological length
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concentric muscle contraction
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-muscle length decreases when contracting
-acceleration -gastrocnemius in terminal stance |
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eccentric muscle contraction
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-muscle increases in length when contracting
-deceleration -shock absorption -soleus in midstance |
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isometric muscle contraction
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-muscle length remains the same during contraction
-produces stability -posture -ex. hip abductors midstance |
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When is EMG activity the greatest: eccentric or concentric contraction?
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concentric contraction
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which type of contraction occurs during walking?
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mostly isometric and eccentric
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How does work change between level, ascent, and descent
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level: 16J/step
descent: 18J/step ascent: 32J/step |
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When does peak muscle activity of the gluteus maximus and adductor magnus occur?
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Heel contact
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What do EMG based studies miss?
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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 |
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What is a new way to study segmental accelerations and powers describing muscle synergy?
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dynamical simulations
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How does muscle coordination, synergy and energy transfer change with age?
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increased antagonist co-activation is a possible adaptation to ensure joint stability with walking in older adults
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Phase of gait with peak muscle activity of the adductor longus
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heel contact
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Phase of gait with peak muscle activity of the gluteus maximus
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heel contact
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Phase of gait with peak muscle activity of the quadriceps
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loading response
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Phase of gait with peak muscle activity of the Gastrocnemius, Soleus, PT, PL, PB, FDL, FHL
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terminal stance
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Phase of gait with peak muscle activity of the adductor longus and rectus femoris
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preswing
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Phase of gait with peak muscle activity of the sartorius, iliacus, gracilis, biceps femoris, AT, EHL, EDL
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initial swing
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Phase of gait with peak muscle activity of the biceps femoris, semitendinosis, semimembranosis, TA
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terminal swing
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What is the soleus's job in gait?
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decelerate internal rotation and forward movement of the tibia during midstance
stabilize the lateral column assist in plantarflexion during terminal stance |
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What is the role of the gastrocnemius
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flex the knee during
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What is the role of the extensor muscles of the leg?
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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 |
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what is the role of the hamstrings during gait
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most active in terminal swing
resist excessive flexion of the knee |
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What happens when you apply a 4 degree forefoot varus/medial wedge to a normal foot?
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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 |
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what happens when you apply a 10 degree varus/medial forefoot wedge to a normal foot?
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The midtarsal joint can supinate 4-6 degrees. The remainder of the supination must be from the subtalar joint.
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What happens when you apply a 4 degree valgus/lateral wedge to the forefoot (normal foot)?
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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 |
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What happens when you apply a 10 degree valgus/lateral heel wedge to a normal foot?
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the lateral forefoot is off the ground.
GRF are unequal at the heel. over time the foot will sublux |
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What happens when you apply a 4 degree varus wedge to the rearfoot of a normal foot?
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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 |
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What happens when you apply a 4 degree valgus wedge to the rearfoot of a normal foot?
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midtarsal joint: supinate
subtalar joint: pronate the forefoot will be inverted relative to the ground ankle: supinates tibia and femur: internally rotate |
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rearfoot deformity
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position of the rearfoot relative to the floor when the subtalar joint is in neutral position (neutral calcaneal stance position)
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total rearfoot deformity=
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neutral calcaneal stance position
subtalar joint neutral position + tibial influence |
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neutral calcaneal stance position is the sum of:
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subtalar joint neutral position + tibial influence
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subtalar joint neutral position
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the frontal plane relationship of the leg bisection to the calcaneal bisection while the subtalar joint is in neutral position
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tibial influence
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the frontal plane relationship of the tibia to the ground while the subtalar joint is in neutral position
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What kind of deformities affect tibial influence?
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Frontal plane deformities like:
genu varum/valgum tibial varum/valgum |
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How do you calculate rearfoot deformity?
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tibial influence + Subtalar joint neutral position
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rearfoot varus
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the rearfoot is inverted with respect to the ground when in neutral calcaneal stance position
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What are the 2 possible components of rearfoot varus?
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subtalar joint varus and/or varus tibial influence
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What are some causes of subtalar joint varus?
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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) |
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tibial varum
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bowing of the lower 1/3 of leg (inadequate ontogenous change)
pathophysiological bowing (rickets,etc) hypoplasia of medial tibial epiphysis |
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compensation
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the way the body responds to a deformity or abnormal function
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compensated or fully compensated
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GRF are equal across the STJ axis/plantar aspect of the heel/plantar aspect of the foot
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partially compensated
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GRF cannot be equalized because a fully compensated position is unable to be reached
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uncompensated
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no motion has occurred to provide compensation
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overcompensated
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motion has occurred beyond what was required for full compensation
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Where do we measure compensation?
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relaxed calcaneal stance position
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What are the 3 components of relaxed calcaneal stance position?
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deformities in all 3 planes:
frontal plane deformities sagittal " " transverse " " |
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Give an example of a frontal plane deformity:
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genu varum/valgum
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give an example of a sagittal plane deformity:
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equinus deformity
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give an example of a transverse plane deformity:
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metatarsus adductus
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compensation for rearfoot varus:
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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 |
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in order to figure out compensation (relaxed calcaneal stance position) for any forefoot and rearfoot deformities you must know or figure out:
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1. STJ inversion and eversion
2. STJ neutral position 3. tibial influence 4. maximally pronated position 5. where fully compensated would be |
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How do you calculate subtalar joint neutral position?
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(inversion + eversion)/3 -eversion
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how do you calculate neutral calcaneal stance position?
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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 |
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How do you calculate the point of maximal pronation of the rearfoot?
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Tibial influence + subtalar joint eversion
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subtalar joint neutral position
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the frontal plane relationship of the leg bisection to the calcaneal bisection while the subtalar joint is in neutral position
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tibial influence
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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 |
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rearfoot varus can be caused by what 2 things
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varus tibial influence
subtalar joint varus |
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compensated or fully compensated
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GRF are equal across
-the the STJ axis -plantar aspect of the heel -plantar aspect of the foot |
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partially compensated
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at the end of range of motion, a fully compensated position is unable to be reached
GRF are unable to equalize |
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uncompensated
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no motion has occurred to provide compensation
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overcompensation
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motion has occurred beyond what was required for full compensation
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relaxed calcaneal stance position
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STJ position as a result of compensation for deformities in all three planes.
frontal: genu varum/valgum sagittal: equinus transverse: metatarsus adductus |
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where will GRF be in a rearfoot varus deformity?
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lateral to the subtalar joint axis
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What will the midtarsal joint do to compensate for the rearfoot varus?
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nothing, it is already maximally pronated
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What will the subtalar joint do in rearfoot varus?
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it will pronate until GRF is equal across
the subtalar joint the plantar aspect of the heel the plantar aspect of the foot |
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in a rearfoot varus deformity how far does the subtalar joint pronate
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until the calcaneus is perpendicular or until the end range of pronation,
whichever comes first |
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maximally pronated position
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Tibial influence + subtalar joint eversion
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fully compensated rearfoot varus deformity
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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 |
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uncompensated rearfoot varus
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NCSP= RCSP
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rearfoot valgus
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rearfoot is everted with respect to the ground when standing in NCSP
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What is rearfoot valgus composed of?
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subtalar joint valgus
valgus tibial influence very rare |
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valgus tibial influence
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genu valgum
tibial valgum |
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rearfoot valgus
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GRF will be on the medial side of the foot medial to the MTJ and STJ axes providing an external supinatory movement
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Where does compensation take place in rearfoot valgus?
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longitudinal midtarsal joint axis which is able to supinate 4-6 degrees to compensate
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What happens if rearfoot valgus is greater than 4-6 degrees
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the subtalar joint may help the longitudinal midtarsal joint and also supinate
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What happens to the forefoot when the longitudinal midtarsal joint supinates?
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it makes the forefoot unstable
supination decreases the ROM available at the midtarsal joint |
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what happens to the subtalar joint when a deformity places the STJ in an everted position of greater than 5 degrees?
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it is forced to go to the end range of pronation
forefoot supinatus is likely to develop |
