GRF ground reaction forces

Question 0

Orientation at Foot flat

Answer 0

Posterior to ankle
Posterior to knee
Anterior to hip

Accept weight, decelerate mass, stabilise pelvis

Ankle plantar flexors
Knee extensors
Hip extensors and abductors

Question 1

Orientation at Heel strike

Answer 1

Posterior to ankle
Posterior to knee
Anterior to hip

Position foot, begin deceleration

Ankle dorsiflexors
Knee flexors
Hip extensors

Question 2

Orientation at Mid stance

Answer 2

Anterior to ankle
Through knee
Anterior to hip

Control ankle, stabilise knee, preserve momentum

Ankle plantar flexors
Knee extensors
Hip extensors and abductors

Question 3

Orientation at Heel off

Answer 3

Anterior to ankle
Anterior to knee
Posterior to hip

Accelerate mass

Ankle plantar flexors

Question 4

Orientation at Toe off

Answer 4

Anterior to ankle
Posterior to knee
Posterior to hip

Prepare for swing

Hip flexors

Question 5

Ground reaction force GRF

Answer 5

Force which acts on a body as a result of the body resting or hitting the ground.
During gait GRFs are multidirectionally orientated due to the position of limbs and postural sway

Question 6

Orientation for GRFs

Answer 6

Proximal/Distal
Anterior/Posterior
Medial/Lateral

Question 7

Measurement Devices

Answer 7

Scales - vertical (proximal/distal) only

Force plates

Question 8

Force plate design

Answer 8

Four piezoelectric transducers
Three orthogonally placed piezoelectric crystals in each transducer
Each crystal measuring GRFs in one direction only.
Force applied to the crystal releases a charge proportional to the applied force.