How EMG Works

For all practical purposes, surface EMG and invasive needle EMG are used for entirely different purposes. Surface EMG is a day-to-day clinical tool and is not intended to replace needle electrodes as used in routine medical electrodiagnostics. Invasive, needle EMG is primarily used as a diagnostic tool to detect very subtle changes of electrical muscle activities. to determine underlying disease processes. Electrodiagnostics may determine that a patient has a thyroid problem, or muscular distrophy, or nerve compression.

Surface EMG on the other hand, is used as a therapeutic tool in two major treatment areas. First, surface EMG is used for biofeedback relaxation. Relaxation applications have a long history and are in common usage. Second, EMG is used in rehabilitation. Rehabilitation applications are only now coming into their own.

For example, an EMG device can give a patient feedback on how hard he or she is exercising an injured muscle. Especially in the early stages of rehabilitation, when it is inadvisable to work against weights, EMG is the only good way to get good information on how hard the patient is working. This informs the clinician quantitatively of the degree of progress being achieved and gives the patient motivation to work diligently at the required work routines.

• Evaluation of muscle function The quantification of weakness used as a baseline to test improvement with therapy. Often an EMG device can detect a very weak voluntary muscle movement which can lead to significant rehabilitation which might otherwise be neglected.
• Evaluation of motor control problems For example, an EMG device can be used to identifiy the location of and quantify the degree of spastic muscle activity following stroke, cerebral palsy, spinal cord injury, etc.
• Muscle training, such as training a patient to contract the quadriceps while in a cast following knee surgery or during uncasted exercise, especially in the early stages when weights cannot be safely used to quantify the strength of the exercise.