KINESIOLOGICAL ELECTROMYOGRAPHY - Biomechanics and Motor Control of Human Movement - page 272

Figure 10.16 Linear envelope processing of the EMG with a critically damped
low-pass filter to match the impulse response of the muscle being recorded. The
full-wave rectified EMG acts as a series of impulses that, when filtered, mimic the
twitch response of the muscle and, in a graded contraction, mimic the superposition of
muscle twitches.

would be achieved with a linear envelope detector with the same cutoff
frequency as used in the mechanical model.

10.3.3 True Mathematical Integrators
There are several different forms of mathematical integrators, as shown in
Figure 10.15. The purpose of an integrator is to measure the “area under
the curve.” Thus, the integration of the full-wave rectified signal will always
increase as long as any EMG activity is present. The simplest form starts its
integration at some preset time and continues during the time of the muscle
activity. At the desired time, which could be a single contraction or a series
of contractions, the integrated value can be recorded. The unit of a properly
integrated signal is millivolt-seconds (mV s). The only true way to find the

average EMG during a given contraction is to divide the integrated value by
the time of the contraction; this will yield a value in millivolts.
A second form of integrator involves a resetting of the integrated signal to
zero at regular intervals of time (40 - 200 ms). Such a scheme yields a series
of peaks that represent the trend of the EMG amplitude with time. Each peak
represents the average EMG over the previous time interval, and the series of
peaks is a “moving” average. Each peak has units of millivolt-seconds so that
the sum of all the peaks during a given contraction yields the total integrated
signal, as described in the previous paragraph. There is a close similarity

·