Measurement of muscle activity Flashcards
Non-sporting applications
Ergonomics
Clinical Diagnostics
Surgery decision making
Product Design
Uses of EMG in sport
Is a muscle active When it becomes active More or less active Does the muscle fatigue Is there Coactivation
What are the neural factors which influence force generation?
the number of motor neurons that are activated (recruitment)
The size of the activated motor neurons
the rates at which they discharge action potentials (rate coding)
Generation of the EMG signal
A nerve impulse causes contraction of the muscle fibres.
The stimulation of the muscle fibre at the motor end-plate produces a reduction of the electrical potential of the cell (depolarisation) which then propagates over the entire fibre before being followed by a repolarisation wave
Generation of the EMG signal
Detection of the potential fluctuations (electrodes)
Signal Transmission (hard wire/telemetry/data logger)
Signal Modification (amplifier)
Storage of the resulting waveform (computer)
Factors affecting the EMG signal
Amplitude
Frequency
Extrinsic - controllable
Intrinsic - uncontrollable
Intrinsic Factors
Physiological
- Number of active MU
- Fibre type
- Blood flow
- Metabolic disorders
Anatomical
- Fibre diameter
- Depth and location of fibres
Extrinsic Factors
Impedance
- Skin prep
- Skin temp
- Gel or no gel
- Impedance tester
Orientation of electrodes
- Parallel with fibres
Location of electrodes
- Not on outside edges - crosstalk
- Not on motor point
- Not on tendon
- Muscle belly
Electrode placement considerations
Consider possible migration of muscle belly
Shortening and lengthening of the muscle
Standardising EMG recordings factors to consider
- Joint angle
- Range of motion
- Movement velocity
- Load/ resistance
- Duration/ repetitions
- Preliminary status
Reducing extrinsic factors
Decreasing electrode size and spacing
placing the electrode on the muscle belly
double differential technique - 3 electrodes
Noise reduction
Use different filters
Tissues: low-pass filter
Electrode to electrolyte interface: high pass filter
Bipolar configuration: bandpass filter
Amplifier: bandpass filter
What is normalisation?
Expression of muscle activity in relative terms
Advantages of normalisation?
Allows comparisons with other muscles, other subjects and between studies.
Eliminates any influence of the detection conditions
Disadvantages of normalisation?
Ability to consistently elicit an MVC varies between individuals
Poor repeatability of EMG from MVC’s
Mechanics of movement – MVC at fixed angle
