9.6 Gait Kinetics

Question 1

What does gait kinetics study?

Answer 1

The analysis of internal and external forces that produce and resist movement during ambulation.

Question 2

What are the main internal forces involved in gait?

Answer 2

Muscle forces and passive tension from connective tissues like ligaments, tendons, and joint capsules.

Question 3

What are the main external forces acting on the body during gait?

Answer 3

Inertia, gravity, and friction.

Question 4

What is inertia?

Answer 4

The body’s resistance to a change in motion.

Question 5

How does inertia affect gait initiation?

Answer 5

It takes effort to overcome inertia when starting or stopping movement.

Question 6

What role does gravity play in gait?

Answer 6

It constantly pulls the body downward, creating weight and requiring muscle control to maintain upright posture.

Question 7

What role does friction play in gait?

Answer 7

It allows foot contact with the ground for propulsion and prevents slipping; too much friction reduces efficiency.

Question 8

What is Newton’s Third Law and how does it relate to gait?

Answer 8

For every action, there is an equal and opposite reaction; the ground pushes back on the foot with the same force it applies downward.

Question 9

What is the ground reaction force (GRF)?

Answer 9

The equal and opposite force exerted by the ground in response to the force applied by the foot.

Question 10

How does the GRF affect the body during gait?

Answer 10

It travels up the leg and influences motion and joint moments at the ankle, knee, and hip.

Question 11

What is the general effect of GRF at the ankle during stance?

Answer 11

It stabilizes the foot and contributes to push-off propulsion.

Question 12

What is the general effect of GRF at the knee?

Answer 12

It creates flexion or extension moments depending on leg position and gait phase.

Question 13

What is the general effect of GRF at the hip?

Answer 13

It loads the joint during weight acceptance and assists forward progression.

Question 14

If a GRF is anterior to the ankle joint, what motion does it cause?

Answer 14

Dorsiflexion.

Question 15

If a GRF is anterior to the knee joint, what motion does it cause?

Answer 15

Knee extension.

Question 16

If a GRF is anterior to the hip joint, what motion does it cause?

Answer 16

Hip flexion.

Question 17

If a GRF is posterior to the ankle joint, what motion does it cause?

Answer 17

Plantar flexion.

Question 18

If a GRF is posterior to the knee joint, what motion does it cause?

Answer 18

Knee flexion.

Question 19

If a GRF is posterior to the hip joint, what motion does it cause?

Answer 19

Hip extension.

Question 20

If the GRF passes directly through a joint, what moment is created?

Answer 20

No flexion or extension moment.

Question 21

What is the center of pressure (COP)?

Answer 21

The point of application of the GRF on the foot during stance.

Question 22

How does the COP move throughout stance phase?

Answer 22

It moves from the posterior heel to between the first and second metatarsal heads at toe-off.

Question 23

When during gait is GRF present?

Answer 23

Only during stance phase, when the foot is in contact with the ground.

Question 24

When is there no GRF acting on a limb?

Answer 24

During swing phase, when the foot is not in contact with the ground.

Question 25

At initial contact (heel strike), where is the GRF relative to the ankle, knee, and hip?

Answer 25

Posterior to the ankle (plantar flexion), anterior to the knee (extension), anterior to the hip (flexion).

Question 26

From foot flat to midstance, how does the GRF change?

Answer 26

It moves anterior to the ankle (dorsiflexion), anterior to the knee (extension), and posterior to the hip (extension).

Question 27

At heel-off, where is the GRF relative to the joints?

Answer 27

Anterior to the ankle and knee (causing dorsiflexion and extension), posterior to the hip (causing extension).

Question 28

At toe-off, how does the GRF shift relative to the knee?

Answer 28

It moves posterior to the knee, changing from an extension moment to a flexion moment in preparation for swing phase.

Question 29

What muscles act to counteract GRF during gait?

Answer 29

Muscles at the ankle, knee, and hip that generate opposing torques to control or assist movement.

Question 30

Why are GRFs important to understand clinically?

Answer 30

They determine which muscles are active and how joint moments change throughout the gait cycle.