2003 : Plantarflexor action
by Chris Kirtley, The
Catholic University of America, Washington DC
The plantarflexors can produce two motions at the ankle when the foot
is on the ground (closed-chain):
Plantarflexion of the ankle and lifting of the body
Posterior rotation of the shank
This table summarizes the power flows in each case:
(Ma = ankle moment, wa =
angular velocity of ankle joint, wf =
angular velocity of foot, Fa= reaction force at ankle, va
= velocity of ankle joint)
|Ankle Joint (muscle) Power (Mawa)
|Active Foot Power Flow (Mawf)
||Positive (into foot)
|Passive Foot Power Flow (Fava)
||Negative (out of foot)
It can be seen that the joint power has the same polarity in each case,
but the power flows are non-zero in the first case and zero in the second.
Email your answers to [n/a]
What makes the effect of the plantarflexor contraction differ
in the two cases?
Why does the foot lift in the first case but stay on the
ground in the second?
Where does the power go in the second case?
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