Surface EMG recordings provide information about aggregate motor unit activity in superficial muscle.The advantage of SEMG is its convenience and good overall correlation to generated muscle force.
In an SEMG recording, a bipolar electrode is placed on the skin surface overlying a muscle of interest. As the muscle contracts, myoelectric activity is revealed as a complex waveform with an amplitude range of about 0-10 mV.
Alternatively, intramuscular EMG techniques may be used where increased signal specificity is required. Intramuscular EMG recordings provide high spatial selectivity allowing for individual superficial or deep muscle groups to be recorded from. This requires the use of fine needle electrodes placed within the muscle of interest.
Because the current source is highly localized with respect to the electrode tip, i.e. only involving a few muscle fascicles, the recorded EMG waveform will appear less complex and is therefore better suited to studies relating motor unit firing rates to generated muscle force. Multiple recording sites may be used within the same muscle group. Like SEMG, recordings using needle electrodes also have amplitudes within the 0 to 10 mV range, although due to being closer to the current source amplitudes will predictably be more toward the higher end of this range.
There are two basic applications of EMG recordings:
Kinesiological EMG - involving the measurement of muscle activity with functional limb movements, postural tasks and exercise trainings.
Neurological EMG - involving the measurement of muscle response timing following artificial stimulation of a motor point
Find out more about use of this signal and related products for specific applications:
LabChart software is designed specifically for life science data and provides up to 32 channels for data display and analysis options that are powerful and easy to use. With auto-recognition of ADI and LabChart Compatible hardware, multi-window views, one touch recording, simultaneous recording from multiple devices, specialized preconfigured settings, easy sharing options and an interface that can be customized to show only the features you want to use.
Placing electrodes directly over a motor point may result in increased frequency in the signal
Action potentials spread in opposite directions from the motor point. A bipolar electrode placed over a motor unit, depending on the geometrics relationship, may results in an increased number of recorded potentials due to phase addition and subtraction of the action potentials. Motor units can be identified using artificial stimulation: the point on the muscle whereby the application of minimal electrical current products a perceptible muscle twitch will correspond to a motor unit.
Thank you for your interest in EMG. Please complete and submit the form below and an ADInstruments representative will aim to get in touch within one working day. If you’d like to speak to someone immediately, office contact information is available from the contact page.