KINESIOLOGICAL ELECTROMYOGRAPHY - Biomechanics and Motor Control of Human Movement - page 266

Figure 10.12 Location of seven surface electrodes placed across the midthigh showing
the region of pick-up for each site relative to the underlying muscles. The zone of
pick-up for each is shown as an arc beneath electrode; there is an overlapping zone
between adjacent electrodes that will result in some cross-talk. Deeper muscles, such
as the vastus intermedius and adductor magnus, require indwelling electrodes whose
zone of pick-up is small because of the small surface area and close spacing of the
electrode tips.
is an evertor and plantarflexor, and LG is a plantarflexor. The results of a
functional test for cross-talk from the PER to the TA and LG is presented in
Figure 10.13. Because it is difficult for many subjects to voluntarily create
a unique contraction (such as eversion for the PER), it is very helpful for
the subject to view the EMG recording and use visual feedback to assist
in the test. Here, we see two very distinct PER contractions. The first was
eversion with a small amount of dorsiflexion: note the minor activity on TA
and negligible amount on LG. The second contraction was eversion with a
minor amount of plantarflexion: note the minor activity on the LG and none
on TA. It is not critical to be successful on both tests simultaneously, or
even on the very first attempt. The student is referred to Winter et al. (1994)
for more details and examples of manual resistance tests.
However, there are many situations when a manual resistance test can-
not be done, and there is a good chance that adjacent channels may have
some common EMG signal. The question is how much do they have in com-
mon? This question was initially addressed by Winter et al. (1994) using
the well-recognized signal-processing technique called cross-correlation (see