EMG Flashcards
Why do we measure muscle activity?
To get a full understanding of muscle activity
What is studying muscle activity useful?
Devising strength and mobility programmes
– Explaining and preventing injuries
– Estimating and calculating internal forces
Define kinesiological analysis
Way in which we analyse human movement is through
analysis
What important factors must be taken into account when using kinesiological analysis?
Muscle tend to pull at both attachments
Many muscles cross more than one joint
What are the four types of muscle actions?
Sustained force movement
Passive movements
Guided movement
Ballistic movement
What are sustained force movements? what do they do?
Force is applied by contracting agonist muscles
– concentric, eccentric, or isometric
• Antagonists are relaxed.
• The sustained force can be
fast or slow, strong or weak
What are passive movements and what do they do?
Without continuing muscle contraction.
– Manipulation - by another force or person.
– Inertial Movement - a continuation of preestablished movements
What are ballistic movements and what do they do?
Compound movement
• 1st phase concentric
• 2nd phase inertial
• 3rd phase eccentric
– deceleration of the joint
What is EMG?
Electromyography (EMG) is a technique for evaluating and
recording the electrical activity produced by skeletal muscles.
It detects the electrical potential generated by muscle cells when these cells are electrically or neurologically activated.
What is EMG measured in?
Volts (V) or microvolts (µV)
What is the peripheral nervous system for?
Branching nerves outside of spinal cord
What is the motor unit for?
Connection between the nervous system an muscle
What happens with depolarisation of the muscle membrance?
Action Potential (AP) travels down the nerve
This creates a voltage difference (neg on outside)
Reaches the muscle and stimulates a muscle AP
that can be recorded
What are the clinical uses of EMG?
Diagnostic
Ergonomics
Decision making before/after
surgery
Neuromuscular or orthopedic impairment
Product design
What are the six sport uses for EMG?
To detect if a muscle is active When is a muscle active If a muscle more or less active To detect if when a muscle fatigue To detect if there is a coactivation Physical activity
What does surface EMG do?
Allows examination of surface muscles
What does in-dwelling EMG do and is it common or uncommon and why?
Allows examination of deep muscles
Not commonly used in sport science as
– Very invasive
– Limited in dynamic contractions
What do you do in the preparation phase on EMG?
Decide on a ‘navigation’ technique to identify electrode location and landmark regions.
Use a pen to mark landmarks and orientation lines. Use a flexible scale band to measure
distances. Follow the SENIAM guidelines.
What happens in the skin preparation phase?
Remove the hair – improves the adhesion of the electrodes especially for sweaty skin types
3. Clean the skin (abrasive vs. sand paper vs. alcohol wipes)
What happens in the sensor location phase?
Attach electrodes parallel to muscle fibres. If possible avoid motor end plates and select
muscle belly portions.
Where should the electrodes not be placed in the sensor location phase?
- NOT on outside edges – crosstalk
- NOT on motor point
- NOT on tendon –
- Between motor point (innervation zone) and tendon – point where muscle begins to twitch with the lowest amount of current
- Muscle belly Orientation of electrodes
- Parallel with muscle fibre
What should you avoid with EMG?
Crosstalk = when the detected signal contains noise from another muscle
• Common in small, close muscles e.g. the forearm
What are the intermediate factors affecting EMG signal?
Detection volume of electrodes
• Filtering effect of electrodes
• Cross-talk from neighboring muscles
What are the three deterministic factors affecting EMG signal?
- Amplitude
- Duration
- Shape
How do you normalise EMG signals?
Processed EMG signals can only be compared with those recorded from the same muscle without removal of the electrodes
.
Can over come this by:
Expressing each data point on of processed EMG as a proportion of a peak EMG from a max isometric contraction of the same muscle processed in the same way
Can tell us how active the muscle is as a % of MVC
