Intro to Biomechanics Flashcards
Biomechanics definition
- Application of mechanical laws to living structures
- Specifically to locomotor system of the human body
Walking definition
- To move at a regular and fairly slow pace by lifting and setting down each foot in turn, never having both feet off the ground at once
Less energy for walking is required when
- There is minimal displacement of the center of mass
- Each moveable segment functions ideally
Series of movements in walking is orchestrated by
- Stable joints
- Muscle actions
- Angular momentum
- Sequential kinematic activity
Components creating joint stability
- Bones and joints
- Ligaments and joint capsule
- Neuromuscular activity
Bones/joints contribution to stability
- Shape of bones
- Design of articular cartilage in bones
Ligaments/joint capsulses contribution to stability
- Provide resistance against ground reactive force
- Prevent unwanted movement
- Support desired joint position
Neuromuscular activity contribution to stability
- Types of muscular contraction
- Agonist, antagonist dynamics
- Joint proprioception
Bones are designed functionally for
- Shock absorption
- Distribution of external stresses
- Muscle attachments
Osseous configuration of bone (examples)
- Anterior lip of tibial plateau
- Anterior medial aspect of calcaneus
- Posterior cuboid
- Lateral process of talus
Knee joint extension (stability)
- Anterior lip of the medial facet of the tibia
- Prevents over-extension of the knee
Calcaneocuboid joint (stability)
- Excessive pronation inhibited by the dorsal “overhang” of the calcaneus
- This creates a close-packed position
Types of joints
- Ball and socket
- Condyloid
- Saddle
- Hinge
Ligament influence on stabilization
- Orientation/angulation
- Joints passed
Muscle contribution to joint stabilization
- Agonist or prime movers
- Antagonists
- Stabilizers
- Orientation to joint
- Pennation
- Type of tendinous insertion
Muscular role in joint movement
- Prime mover
- Antagonist
- Synergist
- Stabilizer
Types of muscle contraction
- Isometric
- Isotonic
Muscle architecture
- Parallel
- Pennate
- Type of muscle fibers
- Relation to joint axis
- Shape of tendon
Proprioception (“sense of self”)
- Conscious: Dorsal Columns
- Unconscious: Cerebellar
Mediators of proprioception
- Muscle spindle monitors muscle length
- Golgi tendon organ monitors muscle tension
- Pacinian corpuscle monitors pressure
Two basic requisites for walking
- Continued ground reactive forces
- Periodic movement in the direction of progression
Center of mass should remain
- In the pelvis
- The body should NOT tip!!!
To keep the center of mass within the pelvis
- It “hovers” at constant height and minimally changing velocity
- Decreased the energy required to walk
Center of mass
- The point where the distribution of mass is equal in all directions
- It does not rely on gravitational pull
Center of gravity
- The point in a body where the forces of gravity vanish
- This may depend on the vertical orientation of the body
- The is the product of mass x gravity
Center of gravity is located
- 2 inches anterior to the second sacral vertebrae
- It follows vertical and horizontal displacement
Center of gravity in anatomical position
- Anterior to S2 vertebra
- At ~ 56% of persons height
- Shifts with body movements
- Balance is dependent upon maintaining the COG above the feet
- Body will compensate by bending and extending
Vertical displacement
- Up and down movement
- Highest point: midstance
- Lowest point: double support
- Average displacement: ~ 5 cm
Horizontal displacement
- Side to side movement
- Lateral limit: midstance (~ 5 cm displacement)
The gait cycle phases
- Stance
- Swing
Stance phase composed of
- Contact
- Midstance
- Propulsion
Contact (stance phase)
- Foot/heel strike
- Loading response ending with full forefoot load
- Foot adapting to terrain and absorbing shock
Midstance
- Full forefoot load to heel off
- Foot converting to rigid lever
- Entire foot is on the ground
Propulsion (stance phase)
- Terminal stance
- Heel off to toe off
- Forward movement of the limb
Swing phase composed of
- Acceleration
- Midswing
- Deceleration
Loading response
- Foot becomes “unlocked” to become a mobile adaptor
- Controlled flattening results in shock absorption
- Limb is actively extending at the hip and knee
- Ends with full forefoot load
Propulsion (stance phase) accounts for
- 33% of stance
- Pre-swing
Pre-swing (propulsion)
- Heel lift
- Toe off
- Foot off loaded
During propulsion
- Muscles working to “shorten” the limb to clear the ground
- Hip and knee flexors
- Dorsiflexion and inversion of foot and ankle
Swing phase in open kinetic chain
- Distal segment moves freely
- Divided into initial swing, mid swing, and late/terminal swing
Initial swing
- Limb is accelerating
Late swing
- Limb is decelerating
- Extending the limb for contact
Six elements of gait
- Pelvic rotation
- Pelvic list
- Knee flexion in stance phase
- Ankle mechanisms
- Foot mechanisms
- Lateral displacement of body
Pelvic rotation
- Rotation about vertical axis
- Transverse plane motion
- Accomplished with flexion and extension of the hip
- Rotation of ~4° on either side of axis
- Increases with speed
Swing leg during pelvic rotation
- Rotates medially
- Rotation is 4° with double support
Goal of pelvic rotation
- Vertical adjustment
- The limbs are essentially lengthened without lowering the COM
Pelvic rotation occurs with
- Forward advancement of the swing limb
- Preparation for heel strike
Pelvic list
- Downward movement in the frontal plane
- Alternating hip movement
Motions in pelvic list
- Adduction in stance
- Abduction in swing
- ~ 5° angular displacement
During pelvic list
- There is a 5° dip on the swinging limb
- This reduces the height of the apex of the curve
The 5° dip on the swinging limb during pelvic list occurs with
- Adduction of the weight bearing limb
- Abduction of the swing limb
Knee flexion in stance phase
- Close to full extension
- Flexes until the foot is flat on the ground (normally ~ 15)
- Moves to extension with full weight bearing
- Then… flexion with heel off
- Elongates and shortens the limb
Combination of pelvic rotation, pelvic list, and knee flexion during stance
- Decrease vertical displacement of COM
- Abrupt displacements still occur
- Walking is still a series of arcs (not a smooth curve)
Foot and ankle mechanisms
- Two intersecting arcs of rotation
- Hell contact
- Heel rise
- Together, smooth out the pathway
Heel contact
- Rotation of ankle about radius formed by heel
Heel rise
- Rotation of the forefoot
Lateral displacement of the body
- Side to side displacement
- ~4-5 cm with each stride
- Slight genu valgum keeps tibia vertical
Lateral displacement is slightly increased when
- Feet are further apart
Lateral displacement is slightly decreased when
- Decreased when feet are closer
