Movement Science Week 9 - Gait Analysis (Transcripts)

Gait Terminology

• The Rancho Los Amigos terminology was pioneered by physical therapist Jacqueline Perry in the mid-20th century, and it became a standardized approach for analyzing gait patterns and movement.
• Regional variations in gait terminology may reflect cultural differences in rehabilitation practices and terminologies.
• Traditional terminology focuses on points in time, while Rancho Los Amigos focuses on phases
• Stance phase is divided into five sub phases: initial contact/heel strike, loading response/foot flat, midstance, terminal stance/heel off, and pre-swing/toe off
• Swing phase is divided into three sub phases: initial swing/acceleration, mid-swing, and terminal swing/deceleration

Gait Phases

• Initial contact/heel strike: 0-2%; the foot first makes contact with the ground
• Loading response/foot flat: 2-10%; the entire bottom surface of the foot contacts the ground
• Midstance: 10-30%; the body's center of mass moves directly over the foot
• Terminal stance/heel off: 30-50%; the heel is off the ground
• Pre-swing/toe off: 50-60%; the toe leaves the ground

Double-limb support

• Occurs twice in the gait cycle: at 10% (beginning of stance) and 50-60% (end of stance)
• Represents when two limbs are in contact with the ground
• Increases in elderly individuals and those with balance disorders
• Decreases as speed increases
• Disappears when running

Single-limb support

• Occurs for 40% of the stance phase
• The body is in single-limb support with the opposite leg between 60-100% of the gait cycle

Gait Kinematics

• Sagittal plane movements: These are the largest and easiest to track, resulting in general consensus regarding values.
• Frontal and transverse plane movements: These are smaller and more difficult to measure, leading to divergent results.
• Center of mass: Located in front of the S2 vertebrae; oscillates in both the sagittal and frontal planes during walking

Center of Mass Movement

• Sagittal plane: Moves up and down twice during one gait cycle
  • Highest point: midstance
  • Lowest point: double-limb support
• Frontal plane: Lateral displacement is about 2 centimeters in each direction (4 cm total)

Pelvis and Hip Movement (Sagittal Plane)

• Pelvis: Tilts anteriorly and posteriorly about 3 degrees during a gait cycle (posterior pelvic tilt at initial contact)
• Hip: Moves through about 40 degrees of sagittal motion
  • Initial contact: Hip flexion, about 25-30 degrees
  • Terminal stance: Hip extension, about -10 degrees (10 degrees of extension)

Body Movements

• The trunk moves forward over the foot during initial contact to midstance, contributing to hip extension
• Hip extension at terminal stance is accompanied by lumbar vertebrae extension

Spatial Characteristics

• Variables that are easily seen by looking at footprints
• Include: step length, stride length, step width, and angle of progression

Temporal Characteristics

• Variables that have to do with time
• Include: speed, step duration, and cadence

Stride Length

• Distance between two successive events of the same foot (usually heel strike)
• At normal walking speeds, one stride length lasts about 1 second and is about 1.4 meters (144 centimeters)

Step Length

• Distance between two successive events of the opposite feet
• Average is about 72 centimeters

Step Width

• Distance between the midpoint of the heel on one foot and the midpoint of the heel on the other foot
• Typically 2-4 inches (5-10 centimeters) for adults

Angle of Progression

• Angle formed between the line of progression and the line that bisects the second and third toes
• Average is about 7 degrees
• Decreases as speed increases

Gait Speed/Velocity

• Distance covered per unit of time
• Important for gait analysis as it influences time, distance, energy expenditure, and muscle activity

Free/Comfortable Walking Speed

• Each person has a unique comfortable walking speed that is most energy efficient
• Often used in gait studies

Speed Effects

• Increased speed: Diminished duration of all gait cycle components (stance, swing, double support); double support time decreases towards zero.
• Decreased speed: Increases stance time; swing time relatively constant; double support time increases

Safety and Walking

• Safety speed: About 30 meters per minute for crossing streets
• Functional distance for community ambulation: 342 meters (parking lot to supermarket and back)
• Average adult gait speed: 82 meters per minute (3 miles per hour)

Cadence

• Number of steps per unit of time
• Usually reported as steps per minute
• Average adult cadence: 113 steps per minute
• Typical adult range: 50-130 steps per minute

Stride Time

• Time to complete one stride (about 1 second)

Step Time

• Time to complete one step### Gait Kinetics

• Kinetics is the analysis of the internal forces that produce ambulation and the external forces that resist the body with each step.

• Internal forces include muscle forces and passive tension from ligaments, tendons, and joint capsules.

• External forces include inertia, gravity, and friction.

• Newton's Third Law states that every action has an equal and opposite reaction, which is exemplified by the forces exchanged between the body and the ground during walking.

Ground Reaction Force

• When a person steps, they exert a force on the ground (driving action), eliciting an equal and opposite reactive force from the ground.
• The ground reaction force is a resultant force, possessing both magnitude and direction.
• It is impacted by the foot, the point of contact with the ground.
• The vertical force directed downwards is the largest of these forces.
• The force represents acceleration or deceleration of the body's forward motion.
• It is greatest at initial contact and at pre-swing.
• Ground reaction forces are measured using a force platform.

Center of Pressure

• The location where the ground reaction force is applied within the foot is called the center of pressure.
• It moves along a path from the heel to the toes throughout the stance phase.
• At initial contact, the center of pressure is lateral to the midpoint of the heel.
• As body weight shifts, the center of pressure progresses to a near-center location in the mid-foot during mid-stance.
• The center of pressure shifts to the forefoot during terminal stance and pre-swing.

Joint Moments & Muscle Activity

• Understanding ground reaction forces is crucial for comprehending muscle activity during gait.
• If the ground reaction force falls anterior to the axis of a joint, the proximal segment of the joint will move anteriorly.
• If the ground reaction force is posterior to the axis of the joint, the proximal segment of the joint will move posteriorly.
• Muscles contract concentrically or eccentrically to counter these external moments.

Gait Cycle & Ground Reaction Forces:

• Initial Contact (heel strike) to Foot Flat:

  • The ground reaction force is posterior to the ankle axis, leading to a plantar flexion moment.
  • This is controlled by an eccentric contraction of the dorsiflexors.
  • At the knee, the ground reaction force is anterior, causing extension.
  • At the hip, the ground reaction force is anterior, causing flexion, countered by hip extensors.

• Foot Flat to Mid Stance:

  • The ground reaction force moves anterior to the ankle axis, promoting dorsiflexion.
  • Plantar flexors control this eccentrically.
  • At the knee, the ground reaction force transitions from posterior to anterior, causing extension.
  • This is aided by a concentric contraction of knee extensors.
  • At the hip, the ground reaction force moves from anterior to posterior, shifting from flexion to extension.

• Mid Stance to Heel Off:

  • The ground reaction force remains anterior to the ankle axis, maintaining dorsiflexion.
  • Gastrocnemius and soleus control this motion.
  • The knee moves from slight flexion to full extension, with an extension moment.
  • The hip continues experiencing an extension moment as the ground reaction force stays posterior.

• Heel Off to Toe Off:

  • The ground reaction force stays anterior to the ankle axis.
  • The ankle moves into plantar flexion due to a concentric contraction of the plantar flexors.
  • At the knee, the ground reaction force shifts from anterior to posterior, creating a flexion moment.
  • At the hip, the ground reaction force stays posterior, maintaining extension.

Kinetic Analysis in Gait:

• Kinetic analysis determines the forces generated during the gait cycle.
• The kinetic parameters are less stereotyped than kinematic parameters.
• Joint moments are the active and passive muscle forces that generate walking.
• These moments are quite variable.
• The support moment is the algebraic sum of the joint moments of the hip, knee, and ankle.
• This moment primarily acts as an extensor, maintaining limb stability and postural control.
• The swing phase reveals less variability in force patterns compared to the stance phase.

Gait Muscle Activation

• Muscles in the stance limb help support the body and contribute to postural control and forward propulsion.
• Swing limb muscle activity is largely confined to the beginning and end of swing phases due to the leg swinging like a pendulum.
• During initial contact, the tibialis anterior and gastrocnemius/soleus muscles co-contract to maintain a neutral ankle, while hamstring muscles decelerate the knee.
• The quadriceps muscles fire to co-contract with hamstrings and prepare the knee for landing, while gluteus medius and maximus muscles stabilize the hip.
• The loading response involves a rapid change from non-weight bearing to weight bearing, recruiting stabilizers to secure the transition.
• Most muscles function eccentrically during loading response due to deceleration, like the tibialis anterior controlling the rate of foot lowering.
• Eccentric control of the quadriceps absorbs shock at the knee, while the gluteus maximus continues to stabilize the hip and prevent trunk flexion.
• During mid-stance, the gastrocnemius and soleus maintain ankle stability, and the quadriceps are relatively inactive.
• Hip abductors and adductors work together to stabilize the pelvis in the frontal plane.
• Force generation for forward limb propulsion occurs in terminal stance primarily through concentric activity of the gastrocnemius, plantar flexing the ankle.
• The hip adductors and flexors contribute to propulsion during pre-swing.
• Hip and knee extensors provide a push from behind during mid-stance, but plantar flexors and hip flexors play a greater role in propulsion.
• Swing phase muscles control momentum, advance the limb, and prepare for stance.
• The iliopsoas and rectus femoris muscles concentrically flex the hip and the tibialis anterior dorsiflexes the ankle during initial and mid swing to clear the foot.
• Maximum knee flexion occurs in mid-swing, primarily driven by pendular momentum rather than active muscle control.
• The gluteus maximus and hamstrings fire eccentrically to decelerate forward motion in terminal swing.
• The quadriceps work with the hamstrings to prepare for weight acceptance and lengthen the step.
• The tibialis anterior maintains ankle stability in neutral dorsiflexion.
• Trunk muscles, including transversus spinal erectors, spine erectors, quadratus lumborum, and internal and external obliques, play roles in counterbalancing trunk flexion during gait.
• The arm swing during gait is under muscular control and contributes to body stabilization and reducing lateral motion of the body's center of mass.
• EMG studies show moderate activity in posterior and middle deltoids during arm swing, with no activity of shoulder flexors.
• The latissimus dorsi and teres major are active as shoulder extensors.
• Triceps activity increases at higher walking speeds, accelerating backward and decelerating forward arm swing.

Adaptation of Gait

• Adaptation to gait involves modifying force generation strategies and postural control strategies.
• Reactive balance strategies are activated in response to perturbations, while anticipatory balance strategies are activated in advance.
• Compensatory adjustments are integrated into the step during recovery from an unexpected perturbation.
• Proximal hip and trunk muscle activity contribute to both steady-state gait and balance recovery.
• A common response to a trip during early swing is an elevating strategy of the swing limb, involving increased hip, knee, and ankle flexion angles.
• Arm movements can be used to counteract backwards fall of the center of mass and act as protection during a fall.
• Proactive strategies for gait adaptation include prediction and visually activated strategies.
• Prediction helps minimize destabilizing forces from body segment movements.
• Visually activated strategies modify gait in response to potential threats to stability in the environment.
• Proactive strategies can be carried out within a step cycle, except for changing directions, which requires planning one step cycle in advance.
• Rules for foot placement during perturbations include increasing step length, placing the foot inside an obstacle, and avoiding crossing the body's midline.
• The decision to step over an obstacle rather than move around it is related to the object's size compared to body size.
• Healthy individuals minimize shifts in mediolateral center of mass during obstacle crossing to maintain balance.
• Walking on slippery surfaces involves reducing stance duration, loading speed, stride length, and angular velocity at heel strike.
• Walking on uneven surfaces initially involves a more cautious gait pattern with increased step width and decreased step length, but practice allows for refinement.
• Foam or compliant surfaces elicit a stiffening response of ankle control muscles to stabilize the limb.
• Walking on compliant surfaces involves lowering the center of mass, inclining the trunk forward at toe-off, and increasing knee flexion.
• The central nervous system adapts mechanics and dynamics throughout the gait cycle to stabilize walking patterns on unstable surfaces.
• Walking on inclines involves greater joint angular motion, increased muscle activity in lower limbs, and adjustments to step length and cadence.
• Curved walking involves changes in stride length, foot positioning, and foot rotation.
• EMG studies show differences in muscle activity during turns compared to walking.
• Initiation of gait from a quiet stance involves relaxation of postural muscles followed by activation of tibialis anterior to move the center of mass forward.
• Steady-state walking is reached within one to three steps, depending on the desired velocity.

Control Mechanisms for Gait

• Gait control involves continuous interaction between central pattern generators and descending signals from the brain.
• Higher brain centers contribute to feedforward modulation of gait patterns in response to goals and environmental demands.
• Sensory inputs, including vision and the vestibular system, play crucial roles in feedback and feedforward modulation.
• Somatosensory inputs contribute to gait stability recovery after obstacle contact.
• Gait ataxia can result from sensory loss, particularly proprioceptive loss from the lower extremities.
• Sensory information from the limbs influences stepping frequency, with joint receptors and muscle spindles contributing to swing phase initiation.
• This information is valuable for gait retraining after stroke, using treadmill walking and hip extension during stance.
• Cutaneous information is important for postural control, particularly reactive balance.
• Somatosensory information plays a role in ensuring normal interlimb coordination.
• Nerve pathology affecting limb coordination significantly impacts gait control.
• Visual flow provides cues about walking speed, with doubling the flow rate leading to increased stride length.
• Visual flow influences body alignment with gravity and the environment.
• Humans use a piloting strategy involving a mental representation of the environment, including topological and metric information.
• Topological information is crucial for obstacle avoidance, while metric information is used in navigation.
• The vestibular sensory system stabilizes the head and gaze, varying forward head rotation and vertical displacement.
• Head stabilization is precise within a few degrees, supported by the vestibular-ocular reflex.
• The amount of cognitive resources needed for gait varies based on task difficulty and movement requirements.

Attentional Resources and Dual-Task Performance

• Researchers use a dual-task design to study how attention is allocated across different tasks.
• Tasks are categorized based on attentional resources required: non-demanded, postural, and cognitive.
• Non-demanded tasks require the least attentional resources, such as sitting or standing.
• Postural tasks like tandem standing, walking, and obstacle avoidance demand more attentional resources.
• Cognitive tasks like cell phone use during walking can significantly impact gait performance and safety, increasing the risk of injury.
• Cell phone use while walking leads to reduced gait speed, fewer objects identified in the environment, and increased risky behaviors while crossing streets.
• Adults often prioritize talking over safe walking, but can flexibly adapt their resources depending on task demands.
• When walking tasks become more complex (e.g., navigating obstacles or carrying items), both speech and gait performance are affected.
• Adults can adjust their gait strategies in response to information about potential hazards (e.g., slipping or falling).
• Young and older adults adopt more cautious gait strategies during dual-task walking, with reduced walking speed, shorter step length, increased step width, and reduced heel contact velocity.
• Obstacle avoidance requires increased intentional resources, and the likelihood of encountering an obstacle increases during dual-task situations.