Electricity
is part of everything the body does.
Electricity
is always flowing in the body; it flows from negatively charged parts of the
body to positively charged parts. As this electricity flows, surface EMG (sEMG)
electrodes can detect and monitor the electrical activity.
Surface EMG electrodes noninvasively record the electrical activity of skeletal
muscles. The unit of measure for the electrical activity is the volt, which is named after Count
Alessandro Volta (who also invented the battery). The detection, amplification,
and recording of changes in skin voltage produced by underlying skeletal muscle
contraction is called electromyography;
the recording thus obtained is called an electromyogram (EMG).
Skeletal
muscles are stimulated to contract by somatic motor nerves that carry signals
in the form of nerve impulses from the brain or spinal cord to the skeletal
muscles. Although a single motor neuron can innervate several muscle fibers,
each muscle fiber is innervated by only one motor neuron. The combination of a
single motor neuron and all of the muscle fibers it controls is called a motor
unit. When a somatic motor neuron is activated, all of the muscle fibers it
innervates respond to the neuron’s impulses by generating their own electrical
signals that lead to contraction of the activated muscle fibers.
Integrated EMG “averages out” noise spikes in the raw EMG
data to provide a more accurate indication of the EMG output level
Muscle activation,
strength, fatigue, or twitch can be
monitored with surface EMG electrodes from a variety of body locations
to study Gait, Range of Motion, Isometric and Isotonic Contraction, Ergonomics,
startle response, etc. sEMG data can be
combined with other data to display muscle response simultaneously with other
physiological events.
