Phasic Muscle Activity Flashcards
what are the 3 phases of stance phase of gait
- contact
- midstance
- propulsive
what are the functions of muscle mechanics
- develop force and power
- dissipate mechanical energy
- stabilize movement until reflexes become active
- redistribute mechanical energy amont body segments
factors affecting muscle strength
fiber type age gender anthropometry (size, length, intersection point from a joint) physiological cross sectional area pennation angle length tension ratio psychological factors fatigue
type 1 slow twitch
aerobic (oxidative metabolism)
fatigue resistant
red (myoglobin)
can work for hrs
type II fast twitch
anaerobic (glycolytic metabolism)
less fatigue resistant
types of type II fast twitch
IIa fast twitch (glycolytic & oxidative, < 30 min)
IIx (glycolytic, < 5 min)
muscle biopsy will show
varying degrees of both types of fibers
how can the proportion of fiber types change
training
pathology: post SCII –> IIx
define psyhiological cross sectional area (PCA)
measure of the number of sacromers that are parallel w/ the angle of pull of the muscle
formula for PCA
PCA = (mass of fibers)/(density of the muscle x physiological length of the muscle)
most muscles have a density of
1.056g/cm3
muscle strength is affected by
orientation of the fibers
orientation of pennation fibers
are at an angle from the long axis of the muscle (tendon axis)
angle = pennation angle
pennation angle affects the muscles ability to
produce power by change the PCA of the muscle
an increase in pennation angle — as the muscle shortens
increases
type 1 slow twitch
aerobic (oxidative metabolism)
fatigue resistant
red (myoglobin)
can work for hrs
type II fast twitch
anaerobic (glycolytic metabolism)
less fatigue resistant
myofiber is composed of
many myofilaments
muscle biopsy will show
varying degrees of both types of fibers
how can the proportion of fiber types change
training
pathology: post SCII –> IIx
define psyhiological cross sectional area (PCA)
measure of the number of sacromers that are parallel w/ the angle of pull of the muscle
formula for PCA
PCA = (mass of fibers)/(density of the muscle x physiological length of the muscle)
most muscles have a density of
1.056g/cm3
define eccentric muscle contraction
the muscle length increases while contracting
produces deceleration
associated with shock absorption
ex. soleus at midstance (decelerates the forward momentum of the tibia)
orientation of pennation fibers
are at an angle from the long axis of the muscle (tendon axis)
angle = pennation angle
pennation angle affects the muscles ability to
produce power by changing the PCA of the muscle
an increase in pennation angle — as the muscle shortens
increases
muscles are STRONGEST at what muscle length tension ratio?
at their physiological length
does passive force build up when the muscle is at its resting length or less
no
myofiber is composed of
many myofilaments
each myofibril contains — myosin filaments and — actin filaments
1500
3000
the distance between the two Z discs is
one sacromere
during muscle contraction what happens to the thin (actin) and thick (myosin) filaments?
thin (actin) filaments slide inward past the thick (myosin) filaments pulling the two Z discs closer together, thus shortening the sacromere
what are the 3 types of muscle contraction
- concentric
- eccentric
- isometric
define concentric muscle contraction
the muscle shortens while contracting; produces acceleration
ex. gastronemius at terminal stance
define eccentric muscle contraction
the muscle length increases while contracting
produces deceleration
associated with shock absorption
ex. soleus at midstance (decelerates the forward momentum of the tibia)
define isometric muscle contraction
the muscle length remains the same while contracting
produces stability
primary in postural muscles
ex. hip abductors in midstance
the overall force of a muscle is the sum of
the active force, Fa and the passes force, Fp
the active force results from
voluntary contraction of the contractile elements of the muscle
the passive force results from
elongation of the connective muscle tissue beyond its resting length
does passive force build up when the muscle is at its resting length or less
no
the muscle force — with increasing shortening velocity
decreases
what is EMG
is the summation of many asynchronous motor unit action potentials
EMG amplitude is dependent on
number of recruited motor units
firing rates and synchonization
MAKE CARDS ON
UNDERSTAND THE ROLE OF MUSCLE IN JOINT MOTION AND ONWARD
