Critical analysis of techniques for normalising electromyographic data : from laboratory to clinical research

Includes abstract.Includes bibliographical references (p. 185-201).Measurements of muscle activity derived from surface EMG electrodes are variable due to both intrinsic and extrinsic factors. The intrinsic factors are endogenous in nature (features within the body) and include muscle fiber type, muscle fiber diameter and length, the amount of tissue between muscle and electrode, and depth and location of muscle with respect to the placement of electrodes (24). These biological factors vary between subjects and cannot be controlled. The extrinsic factors are experimental variables which are influenced by the researcher and can be controlled to some extent. Examples of extrinsic factors include the location, area, orientation, shape of electrodes and the distance between electrodes (interelectrode distance). In order to measure biological variation in the EMG signal, which is important in studies where surface EMG is used to gain understanding of physiological regulation, it is important to minimise the variation caused by these factors. This is in part achieved through the appropriate method of normalisation. The isometric maximal voluntary contraction (MVC) has been used as a standardmethod of normalisation for both static and dynamic exercises. However, researchers have recently improved the methods of normalisation by developing alternative techniques for the measurement of EMG during dynamic activities. By using the same type of movement for normalisation as during the trial, experimental errors can be reduced. The appropriate method of normalisation is defined as a method that is capable of showing repeatability, reliability (low intra-subject variation) and sensitivity to changes in EMG amplitude that is due to biological change and not the contribution of experimental factors. The aim of this thesis was to critically analyse alternative methods of EMG normalisation during dynamic exercise. The data should provide possible guidelines to researchers who are planning studies involving measurement of EMG activity during cycling, running and in clinical populations. Furthermore, the thesis aimed to illustrate that decisions regarding the most appropriate method of normalisation should be based on the study design, research question (absolute muscle activity or changes in muscle pattern) and the muscles being investigated