CROSSTALK IN SURFACE ELECTROMYOGRAPHY - THEORETICAL AND PRACTICAL ESTIMATES

The purpose of this paper is to address four aspects of surface electr omyography associated with crosstalk between adjacent recording sites. The first issue that is addressed is the potential crosstalk between electrodes located on muscles with different functions: antagonist pai rs, or muscles with one common and one different function (i.e. soleus /peroneus longus or soleus/gastrocnemius). Practical functional tests are utilized to demonstrate the crosstalk between muscle pairs to be n egligible. The second goal is to estimate the depth of pick-up and the crosstalk between myoelectric signals from agonist muscles using a th eoretical model. The depth of pick-up was estimated to be 1.8 cm (incl uding a 2 mm layer of skin and fat) using electrodes of 49 mm2 with bi polar spacing of 2.0 cm. A cross-correlation technique is demonstrated which predicts the common signal (crosstalk) between surface electrod es with electrode-pair spacing of 1 cm around a hypothetical muscle. T he predicted crosstalk using cross-correlation measures was 49% at 1 c m electrode-pair spacing dropping to 13% at 2 cm spacing and 4% at 3 c m. The third part compares these predictions with crosstalk measures f rom experimental recordings taken from electrode pairs spaced 2.5 cm a part around the quadriceps. At 2.5 cm spacing there was 22-24% common signal dropping to between 4-7% at 5 cm and to between 1 and 2% at 7.5 cm. The fourth and last component of this report assesses three metho ds to decrease the range of pick-up and thereby potential crosstalk: e lectrodes of smaller surface area, reduced bipolar spacing and mathema tical differentiation. All three techniques reduce the common signal b y varying amounts; all three techniques combined reduce the predicted crosstalk for the 1.0 cm electrode-pair spacing from 49-10.5%.