Biomechanics of Gait

Gait Analysis

• A gait cycle consists of two strides, including stance and swing phases.
• In normal gait, the force vector acts slightly behind the knee in early stance phase.

Ground Reaction Forces (GRF)

Vertical Forces

• During constant velocity walking, the vertical force graph has two hill shapes of equal magnitude.
• F1: upward deceleration of the Centre of Gravity (COG) or weight acceptance (peak arrest).
• F2: COG moving over the stance limb (mid stance) or push-off rate.
• F3: upward acceleration of the COG (peak thrust) or propulsion.

Horizontal Forces (Anterior Posterior)

• The horizontal force graph has a dip and hill shape.
• F4: peak braking (arrest).
• F5: mid support (Fy = 0 BW due to change of direction).
• F6: peak propulsion (thrust).

Pathological Gait

• Deformity: affects mobility, preventing sufficient mobility to attain normal postures and Range of Motion (ROM).
• Muscle weakness: disuse muscle atrophy or neurological impairment, e.g., aging, motor neuron disorders.
• Classic signs of muscle weakness include hesitant gait initiation and jerky movements.

Clinical Gait Analysis

• Collect client data to identify gait deviations and determine causes.
• Review relevant medical data and referring notes from other health professionals.
• 3D motion analysis is the most reliable method.

Kinetics of Normal Healthy Walking

• The force vector acts slightly behind the knee in early stance phase.
• In normal gait, the force vector acts upwards and backwards during initial contact.
• At mid stance, there is a vertical force acting upwards and no horizontal force (pure vertical force).
• At toe off, there is a positive horizontal and vertical force acting upwards and forwards through the body.

Kinetic Differences between Walking and Running

• Changes in the proportion between the impact peak and active peak, with the active peak being larger in running.
• Horizontal force curve changes with a shorter start time and increased magnitude of forces.
• Running downhill increases the impact peak and decreases the active peak, while running uphill has the opposite effect.

Muscular Roles

• Swing: H3, K4, and K5 (heavy quad contribution).
• Braking: H1, K1, K2, and A1.
• Propulsion: H2, A2, and K3.

Abnormalities

• Anterior trunk bending: force vector acts in front of the knee, often due to poor quad strength.
• Posterior trunk bending: force vector acts behind the knee and hip, often due to poor hip extensor strength.