Symposium introduction: electromyography interpretation and limitations in functional analyses of musculoskeletal systems

Electromyography (EMG) has played an important role in studies of musculoskeletal function for over half a century (Moyers 1949; reviewed by Loeb and Gans 1986). The technique has provided important insight into how neuromotor systems control the intrinsic and extrinsic dynamics of musculoskeletal mechanics. The conservation and evolution of motor control during feeding has been examined extensively within the context of a symposium, in order to synthesize studies across phylogenetic groups (Alfaro and Herrel 2001 and papers in that issue). Currently, EMG is an important technique in an integrative framework of experimental research; however, the interpretational potential, and the limitations to the technique in an integrative context have rarely been debated (this issue; Amer Zool, Vol. 41). As shown by most papers in the present issue, the use of EMG in conjunction with several more modern quantitative techniques is a powerful method for quantification of the complex dynamic relationships that exist at the different organizational levels of musculoskeletal form and function. Inconsistencies among EMG protocols that spanned decades may lie at the root of the pronounced variation in collection and analyses of muscle activity data (Wainwright et al. 1989; Wainwright 2002). Consequently, it remains uncertain whether the variation in the magnitude of muscle-specific recruitment reported for closely related taxa are caused by technical incompatibilities between studies in different laboratories (Sanford and Lauder 1989; Wainwright et al. 1989; Konow and Sanford 2008) or by real biological differences. This variation, whether a technical artifact or biologically true, may potentially obscure some biologically informative variation. Analyses and interpretation of emerging phenomena such as regional specialization within individual muscles (Herrel et al. 2008; German et al. 2008) and asynchronous activity in bilateral muscles during feeding (Gerry et al., manuscript in preparation) or locomotion (Higham et al. 2008) further contributes to the complexity of EMG collection, analyses, and interpretation. Expanding from a previous SICB symposium on motor function (2001, see Amer Zool, Vol. 41), it is still clear that a debate on the interpretation of EMG data in an integrative experimental context is overdue. Such debate may foster a broader understanding of the interplay between biological mechanisms and inconsistencies in EMG protocol in producing a pattern of labile muscle-activity within individuals and species, and conservative motor patterns at evolutionary levels. Ultimately, the adoption of an EMG consensusprotocol would allow quantitative comparisons of homologous muscles performing mechanically comparable tasks across a broad phylogenetic sample. Therefore, in the inaugural Late Breaking Symposium at the 2008 meeting of the Society for Integrative and Comparative Biology we examined the general interpretational advantages and limitations of EMGs and the relative importance of incompatibility between EMG protocols, with the overall goal of setting a consensus for future studies. The aim was to facilitate successful incorporation of EMG analyses into quantitative analyses of assemblage-level functional disparity, synchronized with other classical techniques such as cinefluoroscopy and high-speed video, and modern techniques like sonomicrometry, and recordings of strain, force and pressure. Furthermore, we hoped to discuss the progress on some of the target areas of research identified at the 2001 SICB motor-symposium and generate recommendations for future areas of study.