Lever Arms, Rockers, and GRF's Flashcards
What are lever arms?
rigid structures through which a force can be applied to produce rotational motion about a fixed radius
How are lever arms determined?
By the perpendicular distance between the action of the vector (GRF) and the center of joint rotation
Define ground reaction force (GRF)
the force exerted by the ground on a body in contact with it
The rotational potential of the forces that act on a joint is called _____.
torque
Torque (M) = ______ x ______
amount of force (F) x lever arm (L)
The ground reaction force vector is the _____ load-bearing line, which takes into account the forces acting in all 3 planes.
mean
From initial contact through loading response there is a ____flexion moment. Explain why…
plantar
Because the force vector is behind the ankle
From midstance through toe-off there is a ____flexion moment. Explain why…
dorsiflexion
Because the GRF vector moves from behind the hell towards the forefoot
Orthotists describe _____ transitional periods, or rockers, during stance phase of walking as the body progresses forward over the foot.
three
Describe what happens during the first rocker
There is controlled lowering of the foot from neutral ankle position at initial contact to a plantarflexed foot flat, as well as acceptance of body weight on the limb during loading response
Where is the fulcrum at during the first rocker?
the heel
What muscles are active during the first rocker?
eccentric contraction of the quadriceps and anterior tibialis prevents “foot slap” and protects the knee as GFR is translated upward toward the knee
During the first rocker the foot ____ with flattening of medial arch, and thehind foot is positioned in ____ to allow absorption
pronates
valgus
What are 3 situations in which the first rocker is lost?
- heel pain (plantar fasciitis, bone spur, etc.)
- fixed equinus (foot lacks dorsiflexion, toe walkers)
- true or apparent Lower Limb Deficiency
Describe what happens during the second rocker
The tibia begins to rotate over the weight-bearing foot, from its initial 10 degrees of plantarflexion at the end of loading response, then through vertical into dorsiflexion as midstance is complete
What muscles are active during the second rocker?
Eccentric contraction of the gastroc and soleus muscles puts on the brakes to control the speed of the forward progression of the tibia over the fixed foot throughout midstance
During the second rocker there is maximal _____ of the foot
pronation
Describe what happens during the third rocker
The forefoot is converted from its mobile adaptor function of early stance to a rigid lever for an effective late stance, and the heel rises off the ground so that the body weight has to roll over the first metatarsophalangeal joint through push-off in terminal stance
During the third rocker the foot moves into _____ and the heel is positioned in _____.
supination
varus
What muscle locks the midfoot during the third rocker so that the foot can act as a rigid lever?
tibialis posterior
What are 3 situations in which the third rocker is lost?
- painful forefoot (Hallux valgus/hallux rigidus)
- excessively stiff toe of prosthesis
- loss of PF (neuromuscular, stiff hindfoot, ruptured Transverse Arch)
In summary:
1st Rocker Phase occurs during _______
2nd Rocker Phase occurs during _______
3rd Rocker Phase occurs during _______
Heel Strike
Stance Phase
Toe Off
What are 4 functions of prosthetic feet?
- provide controlled plantarflexion at loading response
- provide easy movement from hindfoot to forefoot
- control large dorsiflexion moment at terminal stance to prevent collapse over the ankle
- may try to give some motion at the MP joint (in some prosthetic feet)
What are 2 things prosthetic feet may not be able to eliminate?
- a loss of plantar flexion during pre-swing
- a loss of dorsiflexion during swing phase
