Surface Electromyography (SEMG)

Posted by Dr. Lev Kalika on Wednesday, April 4, 2012 · Leave a Comment

What is it?

Our muscles generate electricity when they contract. This electricity from muscles or muscle groups, changes depending on the effort needed to maintain a certain posture (e.g. sitting at a computer) or to move (e.g. walking, running, lifting). In essence it is the muscles electricity that allows us to sit or stand and perform all types of movements from the most basic to more skilled movements.

Surface Electromyography (SEMG) is a measurement of the muscles electrical activity from the surface of the skin and displayed in the form of a graph (line graph or bar graph. (figure 1)

The small electrical current that comes from active muscles is detected by the electrodes/sensors placed directly on the skin (similar to a Band-Aid) directly above the muscles (Figure 2 shows electrodes placed on the muscles of the leg).

The height (amplitude) and pattern of the signal is displayed onto a computer and the data is collected in a software program to create useful information and reports regarding muscle function.

Generally speaking, the more active the muscle, the higher the line on the graph.

Advantages of SEMG

1. SEMG recording is not invasive and painless. Recording electrodes are attached to the surface of the skin and clips are attached to the electrodes.

2. SEMG helps to eliminate some of the guessing as to how well the muscles are working during the assessment as well as during treatment. Because it is more sensitive to small changes in activity, SEMG will confirm or refute what we believe is happening in terms of muscle activity with greater accuracy. This allows for a more precise evaluation and aids in the direction of treatment intervention.

3. Muscle activity can be objectively quantified, and documented. Similar to a physician using an EKG to evaluate the heart muscle, SEMG allows for objective documentation of skeletal muscle activity at the initial evaluation as well as over the course of treatment.

4. The SEMG recording may be used as a training tool during therapeutic exercise as well as to evaluate the efficiency of these exercises.

Who uses it?

Clinicians and researchers worldwide use SEMG to evaluate the functional status of skeletal muscles and to assist in neuromuscular training and rehabilitation.

What will it feel like?

The clinician will commonly take away the dead skin by using an alcohol cloth. After this, they will attach electrodes to the skin over the muscles they want to monitor or want you to see. The electrodes have a mild adhesive similar to a Band-aid. Attached to the electrodes will be lead wires which will help transfer the information the electrodes receive from the muscles to the computer or SEMG device.

So as a patient, the only feeling you will have of the equipment are the electrodes and the light weight of the instrumentation (see Figure 2).

You will be able to perform virtually any movement necessary throughout the evaluation and rehabilitation process.

Where are the Electrodes Placed?

On the surface of the skin where dysfunctional muscle activity is suspected.

SEMG Patient Evaluation

During the evaluation we can assess:

The amount of muscle activity used to maintain your common postures to see if there is an imbalance among muscles and muscle groups.
The amount of muscle activity you can generate with maximal effort.
The timing of when certain muscles turn on/off during specific movements related to your specific situation.
If the muscles relax after you finish a movement.
If there is excessive muscle activity near the site of injury or pain.
Patterns of muscle activity during common movements (e.g. walking, running, lifting etc).

SEMG Feedback Treatment

During SEMG Feedback Treatment you can watch the muscle activity on the display to:

Assist in postural corrections to help restore a balance between groups of muscles.
Help reduce activity from overactive muscles.
Help increase activity of under-active muscles
Assist in learning to coordinate (turn on/off) muscle activity during specific movement.
Assist in changing patterns of muscle activity during common movements (e.g. walking, running, lifting etc).