Analysis of electrode position on the relative energy spectrum of simulated and real uterine electromyograms. (a) Relative energy spectrum (RES) computed from simulated signals with three bipolar-electrode positions (see figure 2): d = 0 cm (Pair1), d = 5 cm (Pair2) and d = 8 cm (Pair3). The lowest frequency band has been truncated for a better visualisation of the other frequency bands. Significant differences resulting from the electrode positions are indicated by stars, circles and triangles, (p < 0.05). (b) RES computed from EHG recorded in pregnant women with two electrode positions: d = 0 cm (Median Axis) and d = 5 cm. (*p < 0.05; **p < 0.01). AU, arbitrary units.