The effect of sampling rate on the analysis of digital electromyograms from vertebrate muscle.

Quantitative electromyography is a widely used, powerful method for determining in vivo patterns of muscle activity in diverse animal behaviours. Recent increased capabilities of microcomputers have simplified quantification of the variation in the intensity of recruitment during muscle activity, whereas the times of onset and offset of muscle activity have commonly been determined without computers (reviewed in Basmajian and De Luca, 1985; Loeb and Gans, 1986). Such computer-assisted analyses of the intensity of electromyograms (EMGs) have facilitated correlating movements with muscle activity A key step in the computerized analysis of EMGs is the analog to digital (AD) conversion of the EMG. Mathematically oriented literature has explained how the sampling rate of the AD conversion affects the results of frequency analysis of a signal (e.g. Bloomfield, 1976). However, there is little practical information on how sampling rate affects certain EMG variables such as number of spikes, the product of spike number times mean amplitude, and rectified integrated area, which are all commonly used by zoologists to assess the intensity of muscle activity (Loeb and Gans, 1986). The purposes of this paper are: (1) to determine how sampling rate affects the EMG variables commonly used by zoologists, (2) to show how a choice of sampling rate may affect statistical conclusions of comparisons across species, and (3) to provide some practical recommendations on appropriate sampling rates for analysis for vertebrate EMGs. We chose three preparations which represented diverse behaviours and taxa (fish, amphibians and reptiles) in order to increase the likelihood of obtaining ^MGs that varied greatly in their intensity, duration and frequency character