GRF Flashcards
Vertical GRF
perpendicular to supporting surface
most commonly analyzed in biomechanics
A/P GRF
parallel to supporting surface in the direction of movement
M/L GRF
parallel to supporting surface and perpendicular to direction of movement
First peak of vertical GRF
occurs during loading response
deceleration of downward movement of body
called impact peak
Second peak of GRF
occurs during terminal stance
propulsion/push-off from plantar flexors
Dips of GRF
-occurs during midstance
-dip happens because we accelerate upwards, unloading from ground
-coincides with peak of vertical displacement
A/P GRFs description
-braking force through first half of stance phasev(dips)
-propulsive force during second half of stance phase (peaks)
-average about 20% of bodyweight
M/L GRFs description
-avg about 5% of bodyweight
-medially directed through most of stance phase
How can we tell how much force or torque is acting on each joint?
embedded force sensor
inverse dynamics
Inverse Dynamics
Kinematics
GRF
Anthropometrics
estimation of force and torque acting on a joint based on several measurements
Inverse Dynamics Output
at each lower extremity jt there is a net internal joint force & net internal joint moment
Internal forces and moments (of inverse dynamics)
muscle contraction
passive soft tissue stretch/tension
bony contact forces
External Moments
-represents the torque applied to the joint by external forces
-internal torque is counteracts it
-knee OA is an example
What joint does GRF directly act on?
foot/ankle
Backward Trunk Lean
-causes the GRF vector to shift posteriorly in comparison to hip joint
-shifts external hip moment from flexion to extension, aiding in hip extension
-decreases internal moment hip extensors have to produce
Forward Trunk Lean
-likely shifts the GRF force vector anteriorly
-shifts external knee moment from flexion to extension, aids in knee extension
-reduces internal moment the knee extensors have to produce
This component of the ground reaction force provides information about “braking” and “propulsive” forces during walking
Anterior/Posterior
This component of the ground reaction force generally has two peaks - an impact peak and a propulsive peak
Vertical
This is the method researchers use to estimate joint forces and moments at the ankle, knee, and hip during locomotion
Inverse Dynamics
What is not a contributor to internal forces and moments?
Ground reaction force
Why is it important to consider joint moments as a physical therapist?
Joint moments can be an indicator or predictor of joint pathology
What muscle is not generally active during the loading response of “normal” walking gait?
Iliopsoas
This muscle is active during the loading response and helps initiate hip extension during the walking gait cycle.
Gluteus maximus
This muscle helps eccentrically control knee flexion during initial contact and the loading response of the gait cycle.
Vastus lateralis
This subcomponent of gait refers to one’s ability to dynamically control their trunk and COM in the frontal plane during gait.
Postural stability
This movement construct can be observed by comparing movement of the right and left limbs during gait.
Symmetry
