A non-MVC EMG normalization technique for the trunk musculature: Part 2. Validation and use to predict spinal loads

Estimates of the amount of force exerted by a muscle using electromyography (EMC) rely partially upon the accuracy of the reference point used in the normalization technique. Accurate representations of muscle activities are essential for use in EMG-driven spinal loading models. The expected maximum contraction (EMC) normalization method was evaluated to explore whether it could be used to assess individuals who are not capable of performing a ma ximum exertion such as a person with a low back injury. Hence, this study e valuated the utility of an EMG normalization method (Marras and Davis, A no n-MVC EMG normalization technique, Part 1, method development. Journal of E lectromyography and Kinesiology 2000) that draws upon sub-maximal exertions to determine the reference points needed for normalization of the muscle a ctivities. The EMC normalization technique was compared to traditional MVC- based EMG normalization by evaluating the spinal Loads for 20 subjects (10 males and 10 females) performing dynamic lifts. The spinal loads (estimated via an EMG-assisted model) for the two normalization techniques were very similar with differences being <8%. The model performance variables indicat ed that both normalization techniques performed well (r(2)>0.9 and average error below 6%) with only the muscle gain being affected by normalization m ethod as a result in different reference points. Based on these results, th e proposed normalization technique was considered to be a viable method for EMG normalization and for use in EMG-assisted models. This technique shoul d permit the quantitative evaluation of muscle activity for subjects unable to produce maximum exertions. (C) 2001 Elsevier Science Ltd. All rights re served.