Surface Electromyography (SEMG)
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 muscle’s 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 muscle’s electrical activity from the surface of the skin and displayed in the form of a graph (line graph or bar graph.)
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.
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).