EQUILIBRIUM + REVERSE DYNAMICS Flashcards
dynamometry
direct measurement of force + torques using instrumentation
-often specific to tissues
what is dynamometry NOT good for
full body kinetic analysis of complex movement
inverse dynamics
-process of indirectly quantifying net joint forces + net joint moment from kinematic motion capture data + typically ground reaction force data from force plates
-it is a method involving sequential equilibrium analysis of segments of the kinetic chain of the body starting with a distal segment + moving proximally
what is inverse dynamics good for + not good for
-great for full body joint-wise kinetic analysis
-limited to providing tissue specific info
what are measured with a force plate
-GRF
-free moment
-COP
what are the unknowns of solving equilibrium/inverse dynamics
-joint reaction force
-joint moments
what are the inputs for inverse dynamics problems
-motion capture
-manual measurements
-force plates
for inverse dynamics, where do we always start
distal segment
-this is where forces are known since we use GRF
moment of force
the turning effect of applied forces
force applied that acts through the COM causes what acceleration + what moment of force
-only linear acceleration
-no moment of force
force applied that doesn’t act through COM (force is on only one side of something) causes what acceleration + what moment of force
-linear acceleration
-rotation, moment of force
closer you hit to COM, smaller/larger the moment (turning effect)
smaller
a force causes what acceleration + what moment of force
-net acceleration = 0
-net force = 0
-there is still a turning effect
do pure moments cause translation
no- they are pure torque
force couple
2 opposopposing forces (equal + opposite direction) applied to different ends of a body (different but parallel lines of action) whose effect is a pure torque or moment
what do we use joint reaction force for
-helps us move up the kinetic chain to solve for other joint torques + joint reaction forces
-estimate of the joint contact force
increased co-contraction causes what
higher contact force
what does loading of a joint tell us
says something about the degradation of the cartilage at that joint; joint space becomes very narrow
do joint replacements have a life span
yes
-if someone gets a joint replacement relatively young, will probably need a replacement before they die
instrumented joint replacements
joint replacements with strain gauges (transducer converting force to an electrical change in voltage) + transmitter (so there are no wires sticking out of the joint to directly read joint contact forces
internal joint moment
what you generate with the muscles + tissues of the body
-ex: flexor torque of knee
-roles are to resist load + generate acceleration of that joint
external joint moment
moment being applied; essentially what would happen to that joint of your body if you were to relax
ex: force of gravity, GRF, etc.; force that will move joint in absence of muscle activation
true/false: you may begin inverse dynamics analysis at any segment of the body
false
typically in solving equilibrium + inverse dynamics problems for a segment of the body, what are our unknowns in that are solve for (rather than measured/estimated) in the equilibrium equations? (mark all that apply)
-joint moment
-GRF acting on the segment
-joint reaction force
-force due to gravity acting on the segment
-joint moment
-joint reaction force
which of the following is an accurate description of the process of inverse dynamics?
-using movement kinematics + GRF to calculate over joint kinetics
-using kinematics + GRF to calculate muscle forces
-using joint moments to find body segment accelerations
using movement kinematics + GRF to calculate over joint kinetics
true/false: for inverse dynamics it is good enough to draw a free body as a single point through which all forces touching that body act
false
moving up the kinetic chain (from 1 segment analysis to the next) in inverse dynamics is possible because of…
-Newton’s 3rd law
-Newton’s 1st law
-Hooke’s law
-Newton’s 2nd law
Newton’s 3rd law
-Newton’s 3rd law allows us to move up the chain by applying an equal + opposite joint moment + joint reaction force to the next segment in the chain
true/false: inverse dynamics can tell you how much torque a specific muscle is generating during a complex movement
false
dynamometry has which of the following features?
-it indirectly calculates forces
-it provides a “zoomed out view” of the kinetic strategies of a complex movement
-depending on the instrumentation it MAY BE tissue specific
-it doesn’t require any instrumentation to measure forces
depending on the instrumentation it MAY BE tissue specific
what contributes to a joint torque/moment calculated via inverse dynamics?
-muscles
-bony contact
-all of these
-ligaments
all of these
an isometric contraction should be related to ____
-no mechanical work performed
-positive mechanical work performed
-negative mechanical work performed
no mechanical work performed
what would be the instantaneous power of the force due to gravity at the apex of vertical projectile motion?
consider v1 to be the initial projectile motion velocity, d to be the height of the projection, t to be the flight time up to the apex, and v2 to be the velocity at the apex
-Fg*(v2+v1)/2
-zero
-Fg*d/t
zero
consider the point mass method for calculating work done by the body. what would be the work done if the person ran downhill at a constant velocity over a given nonzero time interval?
-zero
-negative
-positive
negative
what does the area underneath the instantaneous power curve represent?
-work
-impulse
-force
-velocity
work
true/false: gas exchange would be a good way to measure the physiologic cost of the high jump in effort to quantify the mechanical efficiency of the movement
false
mechanical efficiency is used for what type of movements
steady state- running, cycling, etc.
-not something like powerlifting
primary muscles involved in jumps (same for all)
-gluteus maximus
-quadriceps femoris
-gastrocnemius
