A non-MVC EMG normalization technique for the trunk musculature: Part 1. Method development

Normalization of muscle activity has been commonly used to determine the am ount of force exerted by a muscle. The most widely used reference point for normalization is the maximum voluntary contraction (MVC). However, MVCs ar e often subjective, and potentially limited by sensation of pain in injured individuals. The objective of the current study was to develop a normaliza tion technique that predicts an electromyographic (EMG) reference point fro m sub-maximal exertions. Regression equations predicting maximum exerted tr unk moments were developed from anthropometric measurements of 120 subjects . In addition, 20 subjects performed sub-maximal and maximal exertions to d etermine the necessary characteristic exertions needed for normalization pu rposes. For most of the trunk muscles. a highly linear relationship was fou nd between EMG muscle activity and trunk moment exerted. This analysis dete rmined that an EMG-moment reference point can be obtained via a set of sub- maximal exertions in combination with a predicted maximal exertion (expecte d maximum contraction or EMC) based upon anthropometric measurements. This normalization technique overcomes the limitations of the subjective nature for the MVC method providing a viable assessment method of individuals with a low back injury or those unwilling to exert an MVC as well as could be e xtended to other joints/muscles. (C) 2001 Published by Elsevier Science Ltd .