Gait Analysis Flashcards
How is movement broken down?
- whole body dynamics
- neuromuscular function
- leg dynamics
Overall = all provide strength, protection, movement and posture
Fundamental requirements of locomotion
- to support our body weight
- move out centre of mass
- be able to swing our legs
What is the centre of mass?
- point of which the line of action of the weight of an object acts irrespective of the position of the object
- centre of gravity is the same
- point around which a body’s weight is equally balanced, no matter how the body is positioned
What is a torque?
- tendency of a force to produce rotation about an axis/fulcrum/pivot
- when a line of action passes directly through the axis of rotation, no angular motion is induced
- but when a line of action falls some distance from the axis, the force tends to cause rotation
Lever systems
- skeletons are jointed lever systems
- muscles produce/transmit force by developing moments at joints
What are concepts of gait based on?
Newton’s laws of motion (working basic for biomechanics)
- Newton’s first law = an object at rest tends to stay at rest and an object in motion tends to stay in motion at the same speed and direction unless acted upon by an unbalanced force
- Newton’s second law = force is equal to mass times by acceleration
- for every action there is an equal and opposite reaction
Kinematics
- geometry of motion
- spatial and temporal elements
- quantitative
Kinetics
- causes of motion (the forces)
- vectors (line of action and point of application)
Kinematic Variables
- Displacement - change in position (m)
- Velocity - change in position over time (m/s)
- Acceleration - change in velocity over time (m/s^2)
How to get from displacement to velocity to acceleration?
- differentiate each (slope of line)
- backwards by integration (area under plot)
Kinematic variables - spatiotemporal
SPATIO
- step/stride length (m)
- stride frequency (number of strides per unit of time (HZ))
TEMPORAL
- stance & swing times (time period of specific foot patterns)
Kinematic variables - angular kinematics
- describes angular motion
- degrees or radians (360 degrees = 2 pi radians)
- measure in absolute angles or relative angles
How do we collect kinematic variables?
- high speed video initially
- motion capture systems (gold standard)
- inertial sensors
Requirements of high speed video methdology
- shutter requirements
- light sensitive cells
- frame rate
Motion capture systems
- cameras need to orthogonal to each other to see same viewpoint at same time to track position of marker
- 4 or more cameras are standard
- more cameras = reduces error
- calibration of the space is v. important (once cameras are in position, marker position in relation to origin)
- 2 types of marker systems (passive and active)
Motion capture system - types of calibration of space
- intrinsic (inside camera)
- extrinsic (orientation of cameras in relation to each other and the origin)
Calibrations occur in static and dynamic types
- static = fixed point, known lengths, set calibration frame to fill space used for individual cameras, frames accuracy 0.1mm
- dynamic = uses static frame of known length and has a wand, use a bundle adjustment
Motion capture systems - PASSIVE marker systems
- qualisys
- cameras emit IR light and reflect off markers and collected by cameras
- requires manual digitisation
Motion capture systems - ACTIVE marker systems
- markers themselves emit IR light so need battery in them
- emit light in specific sequence and each marker defines a landmark
Inertial sensors
- accelerometers
- gyros
can be used outside the motion lab
not as accurate and sensitive as gold standard motion capture
lots of post-processing work to calibrate them
Types of kinetic variables that we measure
- Ground reaction force (force = mass x acceleration)
- impulse = force x time (Ns) = also known as change in momentum
- work = force x displacement
- power = force x velocity or work/time
- energies (kinetic and potential)
- cost of locomotion (mechanical cost of transport = power/[mass x velocity)
Why is impulse also known as momentum?
Momentum = mass x velocity (kgm/s)
F = Mass x acceleration
F = mass x dv/t
F x time = mass x dv
(see slide)
How are energies used to measure kinetic variables
- kinetic (energy from motion)
- potential (stored energy in an object)
Gold standard of kinetic parameter measuring
Force plates
- strain gauge or piezoelectric
Strain gauge force plates
- cannot record as high frequencies as piezoelectric
- force results in shape/length change resulting in change of resistance
Piezoelectric force plates
- use quartz crystals in 4 corners of force plate
- generates current so don’t need power supply
- more sensitive and greater range of force measurements
- more expensive
- suffer from baseline drift
- can record higher freq. transient effects
How to get ground reaction force from piezoelectric force plates?
- 8 channels as ouputs which are differentials between each quartz
- convert analogue output into mV using scalar factors
- then convert into Newtons
- can plot centre of pressure and inverse dynamics (combine kinetic and kinematic data)
Other methods of measuring kinetic variables?
- pressure mats (only at vertebral plane)
Define gait
- cyclical events of repetitive patterns (legs need to be moved into position)
- can be broken down into a series of named events
- can also talk about gait changing in speed
Phases in gait
Stance - foot in contact with ground
Swing - foot off ground and swung forward
Stride - foot contact to next same foot contact
Step - foot contact to contralateral foot contact
Duty factor - potion of time foot is in contact with ground over a stride
Duty factor
Duty factor > 0.5 (both limbs in contact sometimes = double support) = WALKING
Duty factor < 0.5 (only single limb in contact with ground at one time) = RUNNING
How can gait be associated with speed?
Froude number = v^2/gl (gravitational acceleration and leg length)
Partly speed
Better than duty factor as foot patterns alone don’t always describe gait successfully
Define Normal gait cycle
- normal = standardised set of cycling events
What is normal?
- approximation
- generalisation
- comparison
Highly depends on individual, environment and situation
Normal gait cycle for walking
STANCE Double support I - initial contact - loading response Single support - mid stance - terminal stance Double Support II - pre-swing SWING - initial swing - mid swing - terminal swing
