Did you ever notice the heat of your mobile phone against your ear?
Did you ever feel the warmth of the laptop against your stomach and thighs?
While recording muscle tension, we sometimes observe a signal that is NOT the actual muscle contracting. It is an electrical signal that is recorded with sensors at the location of the body but not produced by the muscles. In some cases, this artifact is caused by the client’s mobile phone or other wireless device being activated even though the ringer function was set to off. Below is an example of an artifact signal that can be hundreds of times larger than the biological muscle (electromyography) or brainwave (electroencephalography) signal as shown in Figure 1.
Figure 1. Surface electromyography recording showing the effect of cell phone located 1 cm (0.4 inches) away from the electrodes (from: Lin, I.M. & Peper, E.,2009).
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