module 7 Flashcards
what is fascia
- appiles to visible CT
- widespread and difficult to compartmentalize (connects different tissues, difficult to isolate individual muscle during dissection)
how does fascia distrbutes stresses across structures?
- develops internal forces when mechanically stretched
- fascia between muscles or tissues (muscle and neurovascular tract) may represent a route of force transmission
what do dissections show in fascia?
show continuity of fascia between muscles in different locations (pec. major, biceps, FCR, pamaris longus)
- requires an integrative perspective on the role of fascia
are muscles independent actuators?
what are important implications?
different evidence supporting both
- important implications:
1. neural regulation of mm force would be infleunced by fascial interactions
2. mechanims of muscle adaptation and pathophysiology would need to be revisited
3. modelling of muscles would need to take into account fascial interactions
explain the evidence that suggests muscles are not independent actuators
*performed in rats
1. force measured at the proximal tendon does not always equal force at the dital tendon
- proximal and distal forces (active and passive) in EDL can be different
- differences persist (but decrease) when the fascia between muscles is cut and other muscles of the anterior compartment are removed
- change in length of one muscle changes the Force-Length relationship of another muscle
- length and force changes of the TA+EDL complex infleunce force transmission from EDL muscle
- force-length relationship of the EDL depends on the properties of muscles and CT structures in its direct env.
typically agonist muscles move together
explain evidence to suggest that muscles are independent actuators?
*performed in cats
- assessing intermuscular force transmission under physiological movements of muscles
hindlimb - infleunce gastroscnemius length on soleus-generated ankle torque
1. manipulating knee angle changes gastrocnemius (and plantaris) length but not soleus
- changing knee angle from 70-140 deg does not infleunce the ankle torque generated by selective activation of the soleus = relative muscle mvmt does not necessarily mean force transmission between these muscles = hence linear force summation between gastro and soleus (do not act simultaneous)
how do we reconcile the findings between in muscles are indep/nt indep actuators?
*non-linearities appear small under physiological conditions
*modeling of muscles as independent actuators appear reasonable
potential explanation: strain of fascia may occur in the toe region of the stress-strain curve during physiological movements (linear portion reached only during suprephysiological displacement)
how do muscles actions influence is muscles are ind/not ind actuators?
*mechanics of isometric/concentric actions are well expalined by the SFT and CB theory
*mechanics of eccentric actions challenge theories - force requirement is largely overestimated - special evolved features allow elongation to take place without damagin the muscle
force-velocity: eccentric movements, what model can account for the increase force in eccentric actions?
cross bridge model can account for the increased force: CB increases, CB distribution distances increase
*but cannot explain force increase for slow stretching velocities and the energy requirements are overestimated - requires refinements
what is residual force enhancement
increasing the long-lasting, steady state isometric force following eccentric action
*are observed during and after the lengthening contraction
what is passive force enhancement?
passive: FE is present after muscle deactiviation
- also present in myofibril level (indicates a sarcomeric property)
- decreases if proceded by a conc action (time cource for infleunce of preceding shortening on FE about 1s)
- disappears in titin is removed
how does titin influence passive force enhancement?
- increasing spring stiffness:
- upon activation, titin binds Ca+ (to the glutamate rich region of the PEVK domain, to the 127 immunoglobulin doman - cardiac)
- results in an increase in intrinsic titin’s stiffness = for a given mm stretch, the change in force developed by the muscle will be larger
*binding of titin’s proximal region to the actin myofilament
in vivo: N2A region of titin binds to actin
in vitro: PEVK domain of titin binds to actin
*think force-stiffness-elongation - MOD 1
*activated - Ca+ and actin bound to titin = highest force for length
