Amplitude and bandwidth of the frontalis surface EMG: Effects of electrode parameters

In the present investigation, the frontalis surface EMG was differentially recorded during static voluntary submaximal contractions. First, mean rectified EMG (MREMG) and EMG signal bandwidth were examined for two different bilateral EMG derivations (superior and inferior) with the electrodes placed in horizontal direction and two unilateral derivations (left and right) with the electrodes placed in vertical direction. MREMG was significantly different between the four derivations but absolute differences were small. Bandwidth also varied significantly with derivation. Second, the influence of inter‐electrode distance and electrode size was examined for unilateral derivations. The influence of inter‐electrode distance on MREMG was significant but the absolute effect was marginal. We suggest that a clear effect is to be expected only within the range of small distances (smaller than 10 mm). The significant effect disappeared when MREMG was expressed as proportion of the MREMG during maximal contraction. This normalization seems to allow better intra‐individual or inter‐individual comparisons of integrated EMG, especially when different recording methods are used. The influence of inter‐electrode distance on bandwidth was not significant. Electrode size had no significant influence on MREMG and bandwidth. EMG power spectra indicated that integrated frontalis EMG can be validly measured only when using recording equipment with a frequency response of 5–500 Hz.