MIDSTANCE (Sagittal plane)

Orientation of ground reaction force vector (GRFV) in sagittal plane

Normal GRF is located

• anterior to ankle joint
• anterior to knee joint
• posterior to hip joint

What effect will this have on joint motion and muscle activation?

During midstance, ground reaction force produces

• a dorsiflexor moment at the ankle joint
• an extensor moment at the knee
• an extensor moment at the hip

The body controls these moments with

• eccentric activity in the ankle plantarflexors
• passive force which develops in the posterior knee structures as they elongate during knee extension; knee muscle activity is unnecessary.
• eccentric activity in the hip flexors

MIDSTANCE (Frontal plane)

Orientation of ground reaction force vector (GRFV) in frontal plane

Normal GRF is located

• lateral to axis of subtalar joint
• medial to knee joint
• medial to hip joint

What effect will this have on joint motion and muscle activation?

During midstance, ground reaction forces produce:

• a pronation moment at the subtalar joint
• a varus moment at the knee
• an adduction moment at the hip

The body reponds to these moments with

• activity in the intrinsic foot muscles, soleus, and other supinator muscles (in order to supinate the subtalar joint make the foot more rigid to bear the body's full weight).
• passive tension in the lateral knee structures. Active force in the tensor fascia lata could contribute to knee stability in the frontal plane
• activity in hip abductor muscles