Final Flashcards
What are the two common methods of recording EMG?
In-dwelling Electrodes and surface electrodes
Name three advantages to using in-dwelling Electrodes.
- Record activity from a single motor unit
- Access to deep musculature
- Little Cross-talk
Name three disadvantages to using in-dwelling Electrodes.
- Can be painful
- Single motor unit may not be representative of the entire muscle
- Limitations with recording dynamic muscle activity
How do Surface Electrodes work?
They record the difference in the electrical signal between two electrodes
Name three advantages to using surface electrodes.
- Easy to record
- Minimal discomfort
- Provides indication of global muscle activity
Name three disadvantages to using surface electrodes.
- Can be used only for superficial muscles
- Signal contaminated by cross-talk
- may affect movement patterns on subject
What are two examples of “noise” in an EMG signal?
Movement of the electrode or cable
Electronics
How does a differential amplifier work in a bipolar EMG? What is the new signal called?
It subtracts the m1-m2
It is called the Motor Unit Action Potential (MUAP)
What is the Henneman Size Principle? Why does the Nervous system recruit the MUs in this way?
The orderly recruitment from small MUs to large MUs
The reason for recruiting MUs in this way is to allow for smooth non-jerky production of force and allows the whole muscle to resist fatigue.
The electrodes must be placed on the muscle belly yet not on the innervation zone (motor end plates). T or F?
True
Where will the EMG not collect a signal on a muscle? Where will the signal be cancelled?
At the Tendon
At the innervation zone
What are three things that an EMG signal can tell us indirectly?
Timing of muscle activity
Force
Muscle Fatigue
What are the two steps of the most common way to process EMG?
- Take the absolute value of the signal (Full-Wave Rectification)
- Take an avg value over a certain time period
What is the electromechanical delay?
It is the delay between the neural activation of a muscle and the development of muscle tension
It lasts approximately 30-50ms, but depends on the muscle and joint.
The EMG-Force relationship is linear. T or F?
False it is non-linear
Does surface EMG of a submaximal contraction increase in amplitude with increaing muscle fatigue? If yes, why?
Yes, because more MUs are recruited to produce the same force
What is gait?
Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate
What are some examples of human gait?
Walking
Running
Sprinting
Crawling
Gait progresses the body along a path while maintaining…
Weight-bearing stability
Conserving Energy
Absorbing shock
What are two reasons why we should we measure walking gait?
- To find out how we walk
- To use walking as a baseline measure to understand differences between healthy and unhealthy populations, Ages, Genders, and Races
Gait analysis involves the measurement of what three measures?
Kinematics, kinetics and EMG
Describe Passive Marker Systems.
Using reflective markers and multiple cameras to analyse the kinematics of a gait
Multiple cameras are needed to digitize each marker and determine the 3D location
Describe Active Marker Systems.
Similar to PMS, but the markers are triggered to illuminate.
Describe Electromagnetic systems.
Track the position(X, Y, Z) and orientation of small sensors.
Used to measure Kinematics
What is an Electrical Goniometer?
an electrical device for measuring joint angles.
simple and inexpensive compared to MoCap
Other than EGs, EMS, PMS, and AMS; what else can be used to measure the kinematics of gait?
Accelerometers
Gyroscopes
Magnetometers
What can be measured using a pressure mat? What is another device that can be used for the same measures?
A basic estimate of force and CoP movement.
A force plate (Better)
Kinetics
What would combining kinematic and kinetics allow us to do?
It would allow us to use inverse dynamics to calculate joint forces, torques and muscle forces
What are the percentages of the stance phase and swing phase that make up the gait cycle?
62% stance
38% Swing
How much of the gait cycle does the double stance occupy?
25%
What are main muscles that are active during the loading phase of the gait cycle?
- Glutes
- Quads
- TA
What are main muscles that are active during the Terminal stance phase?
-Calves
What are main muscles that are active during the preswing phase?
TA
Iliopsoas
What are main muscles that are active during the midswing?
TA
What are main muscles that are active during the terminal swing?
TA
Hamstrings
When does the hip change from extension to flexion during the gait cycle?
just before Toe-off
When does the knee change from max flex to ext during the gait cycle?
during swing
When does the ankle change from plantar to dorsi during the gait cycle?
just after Toe-off
What determines the joint moment?
The muscle moment and the amplitude and line of action of the GRF
What are the three functional tasks of walking?
- Weight acceptance
- Single-limb support
- Limb advancement
What is a mechanical analogy of how we walk?
Inverted pendulum
When is the only major energy expenditure during walking?
The redirection portion
What are the 6 determinants of gait?
- Pelvic Rotation
- Pelvic Obliquity
- Knee flexion in stance phase
- Ankle mechanism
- Foot Mechanism
- Lateral Displacement of body
What are two simple measures that can be used to compare between individuals?
Changes in swing stance ratio
Left/right Asymmetry
What is the purpose of Lateral Trunk Bending? What are some common causes?
to reduce the forces in the abductor muscles and hip joint during single leg stance
Painful hip
Hip abductor weakness
Leg length discrepancy
Abnormal hip joint
In a normal gait where does the LOA of the GRF vector pass with reference to the knee? Where does it pass in an individual who anterior trunk bends?
behind the knee and causes a knee flexor moment
In front of the knee and causes a knee extension moment
What are the four gait abnormalities associated with functional leg length discrepancy?
Circumduction
Hip Hiking
Steppage
Vaulting
What is the centre of mass?
The point on a body where all of the mass of the object can be concentrated
What is the centre of gravity?
The point in a body or system around which its mass or weight is evenly distributed and through which the force of gravity acts
Where is the CoG in a human?
55 to 57% of standing height along the middle
What are the methods in which we can calculate the mass and CofG of a limb segment?
- Reaction Board Method
- Cadavers
- scanning techniques
