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Biological Sensors: EMG Demonstration

Katerina Baxter, Binh-Minh Nguyen, Thea Bueno, Danny Metzger

What are EMGs?

Electromyography (EMG) is the detection of electrical signals from skeletal muscles.

Motor units consist of motor neurons and muscle fibers
The brain sends a signal to the muscles through the motor neurons, generating an action potential

Action potentials of all the stimulated motor units combine to make an action potential train, which is an electrical signal we can detect

Processing EMG Signal

Raw EMG data is very messy, so it needs to be cleaned up before use:

The Myoware EMG sensor gives us the rectified and integrated signal.

We implemented a low pass filter to remove high frequency fluctuations in the signal.

This filtered signal is much smoother and is now ready for use.

Reusable Electrode Sleeve

EMGs in Prosthetics

EMGs in Medicine

EMGs can be used to research and diagnose different diseases relating to nerve and muscle dysfunctions in clinical practice. Needle electrodes, which are inserted into the muscle, are often used to detect specific signals. Below are a couple of examples.

Carpal Tunnel Syndrome

median nerve (runs from the forearm to the palm) is squeezed at the wrist
Symptoms: numbness in wrist, pain in finger, swollen fingers

Amyotrophic Lateral Sclerosis (ALS)

Motor neurons are gradually lost, causing muscles to slowly lose function

More Difficult Task

More Motor Units Activated

Greater Signal From Muscle

The output from the sensor is shown in red and the low pass filtered signal is shown in orange

Motor Unit Diagram

How do we sense these electrical signals?

To optimally detect electrical signals of muscles, two surface electrodes must be placed on the belly of the muscle, the part of the muscle that bulges the most when flexed.
Third EMG reference electrode is placed far from the main detecting surface. In our case, this is located at the elbow away from bicep contraction.

EMG control is by far the most common user interface for powered prosthetic devices. This lets patients use other muscles in their body to control their prosthetic limb.

We used small pieces of conductive fabric as our electrode, since they are able to conduct electrical current. These were sewn onto an athletic sleeve.