Limits of the EMG - Italian research

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Abstract from J Appl Physiol. 2004 Apr;96(4):1486-95.

The extraction of neural strategies from the surface EMG.

Farina D, Merletti R, Enoka RM.

Dipartimento di Elettronica, Politecnico di Torino, Corso Duca degli

Abruzzi 24, Torino 10129, Italy.

This brief review examines some of the methods used to infer central

control strategies from surface electromyogram (EMG) recordings. Among

the many uses of the surface EMG in studying the neural control of

movement, the review critically evaluates only some of the applications.

The focus is on the relations between global features of the surface EMG

and the underlying physiological processes. Because direct measurements

of motor unit activation are not available and many factors can

influence the signal, these relations are frequently misinterpreted.

These errors are compounded by the counterintuitive effects that some

system parameters can have on the EMG signal. The phenomenon of

crosstalk is used as an example of these problems. The review describes

the limitations of techniques used to infer the level of muscle

activation, the type of motor unit recruited, the upper limit of motor

unit recruitment, the average discharge rate, and the degree of

synchronization between motor units. Although the global surface EMG is

a useful measure of muscle activation and assessment, there are limits

to the information that can be extracted from this signal.