Biomechanics Lecture 11: Gait

Introduction to Biomechanics Lecture Series

Overview of the Lecture Series

• Tom Walters introduces the 11th lecture in the biomechanics series, encouraging viewers to review previous lectures for foundational knowledge.

• The focus of this lecture is on the gait cycle, building upon prior discussions about lower extremities (hip, knee, ankle).

Understanding Human Gait

Importance of Normal Gait

• Human gait is unique as it has established norms; most individuals exhibit similar walking patterns.

• Pathological conditions (e.g., cerebral palsy, stroke) can alter gait; understanding normal mechanics aids in identifying abnormalities.

Effects of Pain on Gait

• Injuries or pain can lead to deviations in gait, affecting functionality and societal participation.

Definition and Mechanics of Gait

What Constitutes Gait?

• Gait is defined as the rhythmic alternation of upper and lower extremities for forward movement.

• Analysis typically occurs from a side view due to sagittal plane movements being predominant during walking.

Goals of Normal Gait

• Key goals include:

• Forward progression

• Shock absorption through muscle engagement (glutes, quads)

• Lower quarter mobility with proper joint angles

• Stance stability using hip abductors (gluteus medius)

• Energy conservation to reduce fatigue during movement

Phases and Events of the Gait Cycle

Breakdown of Phases

• The gait cycle consists of two main phases: stance phase (62%) and swing phase (38%).

Stance Phase Events

1. Initial Contact: First moment foot hits ground.

2. Loading Response: Weight transfer onto limb; shock absorption begins.

3. Mid Stance: Body weight directly over one limb; stability maintained by hip abductors.

4. Terminal Stance: Progression over limb before next step; calf muscles control forward motion.

5. Pre-Swing: Transitioning weight off analyzed leg while preparing for swing phase.

Swing Phase Events

1. Initial Swing: Leg begins moving forward after toe-off.

2. Mid-Swing: Tibia becomes vertical; foot remains clear from ground to avoid tripping.

3. Terminal Swing: Knee fully extends in preparation for initial contact again.

Abnormal Gait Patterns

Case Study Example

• An example illustrates an individual with multiple sclerosis exhibiting hyperextension during loading response, indicating abnormal mechanics that hinder effective shock absorption.

Summary of Functional Categories

Three Functional Categories

1. Weight Acceptance:

• Includes initial contact and loading response phases focused on shock absorption.

2. Single Limb Support:

• Encompasses mid stance and terminal stance where body stabilizes on one leg.

3. Swing Limb Advancement:

• Comprises pre-swing and all swing events aimed at advancing the limb for subsequent steps.

Distance and Time Variables in Gait

Key Metrics

• Stride time averages around one second per cycle from initial contact back to initial contact on the same foot.

• Stride length varies between 1.2 to 1.9 meters depending on individual height and leg length considerations.

• Step width measures approximately three to four inches between feet during walking cycles.

Cadence & Velocity Insights

• Average cadence differs slightly by gender—males at about 108 steps/minute versus females at around 116 steps/minute.

• Normal walking velocity is crucial for daily activities like crossing streets safely—averaging about 80 meters/minute impacts community participation significantly.

Understanding Eccentric Muscle Contractions in Gait

Role of Muscles During Shock Absorption

• The knee extensors (quadriceps) and ankle dorsiflexors are primarily active during shock absorption, contracting eccentrically to control movement.

• As the foot lands, the quadriceps help manage knee flexion while the dorsiflexors assist in transitioning from heel strike to a flat foot position.

Loading Response Mechanics

• In the loading response phase, controlled knee flexion is crucial; quads contract eccentrically to prevent collapse under gravity.

• The knee moves from 0 degrees at impact to 20 degrees of flexion, while the ankle transitions into slight plantar flexion.

Transitioning Through Stance Phases

Mid Stance Dynamics

• To move from loading response to mid stance, glutes and quads contract concentrically to propel the body forward.

• The tibia advances as dorsiflexors pull it forward into more ankle dorsiflexion, achieving a straight alignment of the body.

Terminal Stance Challenges

• During terminal stance, calf muscles experience significant eccentric contraction to control forward momentum and prevent falling.

• This phase requires careful management of ankle dorsiflexion through eccentric contraction of plantar flexors despite being pulled by gravity.

Pre-Swing and Initial Swing Phases

Pre-Swing Activity Levels

• Minimal muscle activity occurs in pre-swing as the leg moves behind due to forward progression; critical event is achieving 40 degrees of knee bend.

Initiating Forward Motion

• In initial swing, hip flexors and hamstrings contract concentrically to lift the leg while maintaining toe clearance with dorsiflexor activation.

• Achieving 60 degrees of knee flexion is essential for safe ground clearance during this phase.

Finalizing Gait Cycle Movements

Mid Swing Adjustments

• Continued concentric contractions occur in hip flexors and dorsiflexors as the tibia reaches a vertical position preparing for next steps.

Terminal Swing Preparation

• Knee extensors must contract concentrically for full extension before heel strike; hip extensors switch to eccentric mode for deceleration.

Importance of Knee Extension

• Proper knee extension is vital for normal gait mechanics; deficits can hinder effective heel strike post-knee surgery.

Summary Insights on Gait Mechanics

Comprehensive Overview

• The lecture covers all eight events within a gait cycle emphasizing muscle activities across various phases. Review may be necessary due to complexity.