The measurement of muscle contraction is important for various disorders in the muscular and neuronal system. Muscles get the input to contract from a brain through the neuron at a specific junction. This is accomplished through a generation of an electrical pulse in millivolts (20-30mV) oscillating at a frequency of 7-20Hz. The measurement of this electrical pulse is the basis of the electromyogram.
The electric pulse can be measured by surface electrode for muscles near the surface or can be measured with a fine needle deeper inside the muscle. This measurement is very useful in the understanding of neurological disorders since the pulse to contract is generated voluntarily by the patient.
Tremor is an involuntary and repetitive movement of the hand. Measurement of tremor has been done extensively by this technique and has been important in the classification of tremors into many categories: Essential tremor, Parkinsonian tremor and others dependent on the frequency, amplitude and clinical presentation. It would be interesting to see whether locked-in patients display of activity since it is expected that impairment of motor functions would lead to zero or minimal activity.
EMG has been used to measure human, but also animal muscle movements (it was discovered in animals first!) like salmon and forms an important diagnostic technique. The tools that are used for clinical measurement have been used in a variety of combinations with other measurements including strength measurements and have been computerized with other sensors too.