Does Location Matter Using VMG to Do Muscle Assessment?

One of the cool aspects of the MyoWave Device that measures muscle activity by converting vibration to absolute effort is the ability to determine the optimal locations on the muscle body from which to take measurements.

To find out the answer for two very commonly scrutinized muscles in the thigh we performed a semi-scientific test one recent afternoon.
We attached three vibromyography sensors to the belly of the vastus medialis (VM) on Sara, our willing subject, using elastic straps with a "quiet" hook-and-eye system. With much experience we had determined that Velcro straps simply make too much noise as the loops and hooks get stretched. Admittedly, we have not yet devoted any time to determining whether the frequency of that noise could be readily filtered out - a job for another afternoon.
The first sensor was affixed using an elastic strap about 3 inches above her knee. A second sensor was attached about 2 ½ inches above the first and yet a third was attached a similar distance above the first two.

Sara then performed ten squats and we monitored the effort generated by the VM during each event.

Attachment 904

We repeated the experiment, switching the sensors to her vastus lateralis (VL) and added a fourth sensor even higher than the first three. To ascertain the level of repeatability we had her re-do the VL test, squatting an additional ten times.

The results were consistent and quite interesting and provided insight as to how we ought to advise users of this technology. We found that the lower the position of the sensor on either the vastus medialis and vastus lateralis, the greater the effort recorded. Given all the caveats about the lack of scientific method we used in this afternoon activity, there was no doubt that - in this test with this subject at least - total amplitude of muscle effort was reduced with each successively higher placed sensor. The table below and the accompanying graph describe the correlation between distance from the knee and percentage of signal recorded:
Attachment 905
Attachment 906

We also compared the absolute total effort calculated by the lowest sensor on each of the VL tests (the one 3" above the knee) and determined that the difference between the two sets of squats for that sensor was less than 4%. Obviously, we need to expand this experiment to include other subjects as well as to repeat this with Sara but we decided to share the information nonetheless.