Journal of Electromyography and Kinesiology 14 (2004) 505–514 www.elsevier.com/locate/jelekin The eﬀects of bipolar electrode montage on conduction velocity estimation from the surface electromyogram R.B.J. Beck a , M. O’Malley a, , J.P. van Dijk b , P. Nolan c , D.F. Stegeman b a DepartmentofElectronicandElectricalEngineering,UniversityCollegeDublin,Dublin4,Ireland b DepartmentofClinicalNeurophysiology,InstituteofNeurology,DepartmentofClinicalNeurophysiology,UniversityMedicalCentreNijmegen andInteruniversityInstituteforFundamentalandClinicalHumanMovementSciences,Nijmegen,TheNetherlands c DepartmentofHumanAnatomyandPhysiology,ConwayInstitute,UniversityCollegeDublin,Dublin,Ireland Received 10 March 2003; received in revised form 1 September 2003; accepted 20 September 2003 Abstract This study examines the inﬂuence of the bipolar electrode montage on conduction velocity (CV) estimation. Electrode montage refers to the combination of two parameters, the inter-electrode distance (IED), the distance between the two electrodes of a bipolar pair, and the inter-signal distance (ISD), the distance between two bipolar signals used to calculate CV. Data from the biceps brachii (BB) and tibialis anterior (TA) of healthy subjects are analysed. Two approaches are used for CV estimation. The ﬁrst returns a single value per epoch. The second is based on ﬁnding velocity values from individual peaks in the signal and results in a peak velocity (PV) distribution being generated per epoch. It is concluded that CV estimation is signiﬁcantly depen- dent on the choice of the (IED, ISD) electrode montage. The main results are that the electrode montage aﬀects (1) the mean PV and CV estimates, (typically P< 0:001), (2) the degree of spatial variability, and (3) the width of the PV distributions. The combi- nation of a small IED and large an ISD is recommended. # 2003 Elsevier Ltd. All rights reserved. Keywords: Surface EMG; Electrode montage; Inter-electrode distance; Conduction velocity 1. Introduction Conduction velocity (CV) of a muscle ﬁbre can be deﬁned as the speed with which an impulse or action potential travels along the length of the ﬁbre mem- brane. It may be used as an indication of the physio- logical or pathological state of the membrane. One of the most common applications of CV is the assessment of muscle fatigue [3,19,20,39]. Attempts have been made to diﬀerentiate between normal subjects and myopathic or neuropathic patients based on CV mea- surements [13,35,38]. Whatever the application of CV estimation, a reliable and accurate measurement tech- nique is important. CV values may be determined by a variety of diﬀer- ent time- and frequency-domain techniques, e.g. spec- tral-dip [18], cross-correlation [26], zero-crossing [31], multi-channel maximum likelihood approaches [8] or phase-shift methods [19]. The advantages of the diﬀer- ent techniques have been reviewed [7]. Regardless of the calculation technique erroneous CV values may arise due to incorrect electrode placement and/or orientation. The importance of correct electrode place- ment has been dealt with [4,11,22,25,28,31]. Particular care should be made to ensure that the electrodes are not placed in the vicinity of the end-plate (EP) or the tendon region. If the electrodes are placed too near these regions, non-propagating, ‘far-ﬁeld’ components [34], of the surface electromyogram (SEMG) signal may become dominant. The zero time delay between these non-propagating components can lead to over- estimation of CV. Aside from the positioning of the electrodes, the degree to which ‘far-ﬁeld’ components aﬀect the CV estimate may also be aﬀected by the spa- tial ﬁlter used to derive the SEMG signals, the depth of the source [6] and the method used for CV estimation [7], e.g. time delay estimation techniques based on  Corresponding author. Tel.: +353-1-706-1851; fax: +353-1-283- 0921. E-mail address: mark.omalley@ucd.ie (M. O’Malley). 1050-6411/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jelekin.2003.09.024