Levers, Rockers, and GRFs Flashcards
What is determined by the perpendicular distance between the action of the vector and the center of joint rotation?
Lever arm
What is the mean load bearing line, taking into consideration forced acting in all 3 planes?
Ground reaction force
What is the product of the force times the lever arm (the rotational potential of the forces that act on a joint)?
Torque moment
What is the GRF during initial contact?
PF moment due to force vector being behind heel
What happens to the GRF during midstance?
shifts in front of ankle causing DF
What are the 3 rocker phases?
- heel strike
- stance phase
- toe off
What happens at first rocker (heel strike)?
eccentric quads and ant tib, pronation with flattening of medial arch
What happens at second rocker (stance phase)?
progressive DF of ankle, eccentric gastroc and soleus
What happens at third rocker (toe off)?
foot rotates of met heads, supinates, heel into varus
tib post locks midfoot to act as rigid lever
pushoff via triceps surae contraction
What does a softer heel cause?
quick to foot flat = more stability at knee
What does a firmer heel cause?
better 1st rocker, but more isntability
What does a soft toe cause?
short toe level, small DF moment, high knee flexion moment
What does a rigid toe cause?
long toe lever, high DF moment, high knee extension moment
What does a stiff ankle cause?
more resistance met when moving forward at midstance (rapid increase in DF and knee extension moment)
What does a free ankle cause?
DF moment increases slowly, knee flexion moment
