Gait Analysis: Kinematics & Kinetics

💡 Core Concept: Gait is a translatory progression of the body as a whole, produced by coordinated, rotatory movements of body segments. The goal is to move the body's Center of Gravity (COG) forward with minimal energy expenditure.

1. General Terminology

• Stride Length: Distance from heel strike of one foot to heel strike of the same foot (One complete cycle).
• Step Length: Distance from heel strike of one foot to heel strike of the opposite foot.
• Cadence: Number of steps per minute. (Average adult: 110-120 steps/min).
• Velocity: Speed of walking (Distance/Time). Average is ~1.37 m/sec.

2. Phases of the Gait Cycle

A single Gait Cycle consists of 60% Stance Phase (foot on ground) and 40% Swing Phase (foot in air).

Traditional Term	Rancho Los Amigos (RLA)	Function/Definition
Heel Strike	Initial Contact	Moment the foot touches the ground.
Foot Flat	Loading Response	Shock absorption; weight transfer onto leg.
Mid Stance	Mid Stance	Body passes over the supporting foot.
Heel Off	Terminal Stance	Heel rises; body moves ahead of forefoot.
Toe Off	Pre-Swing	Final push-off; limb unweighting.
Acceleration	Initial Swing	Thigh begins to advance.
Mid Swing	Mid Swing	Thigh continues to advance; knee extends.
Deceleration	Terminal Swing	Knee extends fully to prepare for contact.

3. Energy Efficiency: Saunders' Determinants

To minimize energy, the body tries to keep the Center of Gravity (COG) path smooth (minimizing vertical and lateral displacement). The COG is located anterior to S2.

The 6 Determinants of Gait

1. Pelvic Rotation: Pelvis rotates forward (4°) with the swinging leg to increase reach and minimize the drop of COG.
2. Pelvic Tilt: Pelvis drops slightly (5°) on the swing side (controlled by stance leg Glute Med) to minimize the rise of COG.
3. Knee Flexion in Stance: Knee flexes to ~15° immediately after heel strike to absorb shock and lower the peak of COG.
4. Foot Mechanisms: Ankle dorsiflexion/plantarflexion smooths the path.
5. Knee Mechanisms: Related to ankle motion.
6. Lateral Displacement of Pelvis: Minimizes side-to-side movement.

4. Muscle Activity (Kinetics)

A. Shock Absorbers (Eccentric Control)

• Tibialis Anterior: Fires eccentrically at Heel Strike to prevent "Foot Slap."
• Quadriceps: Fire eccentrically during Loading Response to control knee flexion (shock absorption).

B. Stabilizers

• Gluteus Medius: Fires during Stance to prevent the opposite pelvis from dropping (Trendelenburg).
• Gluteus Maximus: Fires at Heel Strike to prevent the trunk from jackknifing forward (controls flexion moment).

C. Propulsors (Concentric Control)

• Gastrocnemius/Soleus: Fire concentrically at Heel Off (Push-off).
• Iliopsoas/Rectus Femoris: Fire concentrically at Toe Off to initiate Swing.

5. Special Gaits

A. Running

• Double Float: There is a period where neither foot is on the ground.
• No Double Support: Unlike walking, there is never a time when both feet are on the ground.
• Stance Time: Decreases significantly (from 60% in walking to <40% in sprinting).

B. Stair Gait

• Ascent: Concentric dominant (glutes/quads lifting body weight).
• Descent: Eccentric dominant (controlling gravity).

6. Abnormal Gait Patterns

⚠️ Common Pathologies:

• Trendelenburg Gait: Weak Glute Medius. Pelvis drops on the Swing side. Patient leans trunk toward the Stance/Weak side (Compensated).
• Steppage Gait: Weak Tibialis Anterior (Drop foot). Patient flexes hip/knee excessively to clear the toes.
• Antalgic Gait: Painful gait. Shortened stance phase on the affected leg.
• Vaulting: Rising on the toe of the stance leg to clear a long swinging leg (e.g., fused knee).

🏆 Key Points: Biomechanics

• Double Support Phase: Occurs twice in the gait cycle (Initial Contact & Pre-Swing). It disappears in running.
• Ground Reaction Force (GRF): At Heel Strike, the GRF is posterior to the ankle (creating a Plantarflexion moment) and posterior to the knee (Flexion moment).
• The Rockers: 1. Heel Rocker: Heel strike to foot flat. 2. Ankle Rocker: Tibia advances over the foot. 3. Toe Rocker: Push off from metatarsal heads.

📝 20 High-Yield MCQs

Test your knowledge for Exams.

Q1. The Stance Phase comprises what percentage of the normal gait cycle?

A. 40% B. 60% C. 50% D. 70%

Rationale: Stance is approximately 60% and Swing is 40%. In running, stance percentage decreases.

Q2. In Rancho Los Amigos (RLA) terminology, "Heel Strike" is called:

A. Initial Contact B. Loading Response C. Terminal Stance D. Preswing

Rationale: RLA focuses on the phase of motion (Initial Contact) rather than the specific body part (Heel), as some patients may not strike with the heel.

Q3. Which muscle contracts eccentrically at Initial Contact to prevent "Foot Slap"?

A. Gastrocnemius B. Tibialis Anterior C. Extensor Hallucis Longus D. Soleus

Rationale: The Tibialis Anterior lowers the foot to the ground gently. If weak, the foot slaps down.

Q4. The primary purpose of Saunders' "Six Determinants of Gait" is to:

A. Minimize the vertical and lateral displacement of the COG B. Increase walking speed C. Increase ground reaction forces D. Eliminate pelvic rotation

Rationale: By smoothing the COG pathway, metabolic energy cost is reduced.

Q5. A patient with a weak Right Gluteus Medius will exhibit a pelvic drop on which side during Right single-leg stance?

A. Right side B. Left side (Trendelenburg Sign) C. No drop D. Anterior drop

Rationale: The Right abductors stabilize the pelvis. If weak, they cannot hold the pelvis level, so the unsupported (Left/Swing) side drops.

Q6. What is the defining difference between Walking and Running gait?

A. Running has higher velocity B. Walking has double support; Running has a double float phase C. Arm swing D. Heel strike

Rationale: In walking, one foot is always on the ground (and sometimes two). In running, there is a flight phase where neither foot touches.

Q7. At Initial Contact (Heel Strike), the Ground Reaction Force vector passes __________ to the ankle joint, creating a __________ moment.

A. Posterior; Plantarflexion B. Anterior; Dorsiflexion C. Through; Zero D. Anterior; Plantarflexion

Rationale: The heel hits the ground behind the ankle joint axis, forcing the foot down (PF moment), which the Tibialis Anterior must eccentrically control.

Q8. Knee flexion to approximately 15 degrees during Loading Response serves to:

A. Absorb shock B. Increase walking speed C. Clear the foot D. Initiate swing

Rationale: This controlled buckling (eccentric quads) acts as a spring to dampen the impact of weight acceptance.

Q9. "Stride Length" refers to the distance between:

A. Left heel strike and Right heel strike B. Right heel strike and the next Right heel strike C. Toe off and Heel strike D. Steps per minute

Rationale: A stride is one full cycle (Right heel to Right heel). A step is half a cycle (Right heel to Left heel).

Q10. Average Cadence for an adult is approximately:

A. 60-80 steps/min B. 110-120 steps/min C. 140-150 steps/min D. 90 steps/min

Rationale: 110-120 steps/min is standard for efficient walking velocity. Women often have a slightly higher cadence due to shorter leg length.

Q11. Which muscle group fires concentrically to initiate the Swing Phase (Acceleration)?

A. Hip Flexors (Iliopsoas) B. Hip Extensors C. Knee Extensors D. Plantarflexors

Rationale: The hip flexors pull the thigh forward to accelerate the limb into swing.

Q12. The Gluteus Maximus fires at Heel Strike primarily to:

A. Extend the knee B. Decelerate forward momentum of the trunk (prevent jackknifing) C. Plantarflex the ankle D. Abduct the hip

Rationale: Momentum tries to flex the trunk forward at heel strike. The Glute Max (extensor) eccentrically/isometrically stops this.

Q13. A "Compensated Trendelenburg Gait" involves:

A. Pelvic drop only B. Lateral trunk lean toward the weak side C. Lateral trunk lean toward the strong side D. Excessive hip flexion

Rationale: By leaning the trunk over the weak hip, the patient reduces the moment arm of gravity, decreasing the need for Abductor muscle force.

Q14. "Vaulting" is a compensatory mechanism used to:

A. Clear a long contralateral limb (e.g., fused knee) B. Absorb shock C. Decrease velocity D. Reduce pain

Rationale: The patient rises up on the toes of the stance leg to lift the pelvis high enough for the stiff/long swing leg to clear the floor.

Q15. The Center of Pressure (CoP) path during stance travels:

A. From Heel → Lateral midfoot → Medial forefoot (Great toe) B. From Heel → Medial Arch → 5th toe C. Straight down the middle D. From Toes to Heel

Rationale: Normal mechanics involves lateral loading (supination) then medial push-off (pronation/windlass).

Q16. Double Support Phase disappears when:

A. Walking speed is very slow B. Walking transitions to Running C. Climbing stairs D. Walking downhill

Rationale: The defining kinematic difference between walking and running is the loss of double support.

Q17. Which gait parameter typically decreases with Age?

A. Double Support Time B. Base of Support C. Step Length and Velocity D. Stance width

Rationale: Elderly individuals walk slower, with shorter steps, and a wider base of support (increased double support time) for safety.

Q18. During stair ascent (going up), the primary muscle work is:

A. Concentric (Lifting body weight) B. Eccentric (Lowering body weight) C. Isometric D. Passive

Rationale: Going up requires the quads and glutes to shorten (concentric) to lift the body against gravity. Descent is eccentric.

Q19. The "Ankle Rocker" (2nd Rocker) refers to:

A. The heel striking the ground B. The tibia advancing over the planted foot (Dorsiflexion) C. The push-off from the toes D. Swing phase

Rationale: This occurs during Mid-Stance, where the tibia rotates over the fixed talus, controlled by the eccentric soleus.

Q20. An "Antalgic Gait" is characterized by:

A. Decreased Stance time on the painful leg B. Increased Stance time on the painful leg C. Crossing legs (Scissoring) D. High steppage

Rationale: The patient wants to get off the painful limb as quickly as possible, shortening the stance phase on that side.