*4.4. Recording of EMG Signals from Surface, Needle and Wire Electrodes*

There are a variety of methods used to obtain EMG data from humans and animals. As a general construct, there are three types of electrodes: surface, needle, and wire electrode. The neurophysiological characteristics and the interpretation of the data derived are not synonymous. Surface electrodes are placed over the skin; they can be manufactured from a variety of materials and formed into various sizes and shapes. Surface recording over the skin is subject to distortion of the EMG signal due to the interposition of the fascia and the subcutaneous tissues. With limb movement, the skin, the subcutaneous tissue and the muscles move asymmetrically. This contributes further to movement artifact. These tissues are effectively a low pass filter. In comparison, needle electrodes are made of metal; subtypes include monopolar, concentric, single fibre and macroelectrodes. Wire electrodes, in contrast, can vary in diameter and length. Wire electrodes allow for long term implantation in subjects and are generally well tolerated. When compared to surface electrodes, there is less cross-talk. As a conceptual argument, data from wire electrodes aggregates the EMG signal from muscle fibres in multiple motor units. The signal is potentially affected by multiple factors including the proximity of the signal generator to the wire, phase cancellation, size of fibres, and type of fibres (i.e., fast twitch, slow twitch). As well, there is some contribution related to the neural network that controls the agonist–antagonist pair.

The fine-wire recordings from this model are particularly unique. Specifically, the EMG data were obtained prior and subsequent to TSCI. Additionally, the data were obtained while the subjects were moving freely (dynamic movements), over an extended period of time. Some potential limitations include the relatively few numbers of subjects; this is, in part related to cost. As well, the collection of longitudinal nature precluded a very high sampling rate.
