The trade-off between meticulousness and methodological variance in normalization of low back EMG

Abstract

Background: Normalization of surface electromyography (EMG) is a common and recommended practice, however this methodological step itself introduces variability to a data set. Quantification of this variance is necessary to correctly interpret overall EMG variability. This information is also paramount to identifying experimentally and clinically relevant normalization task(s) which minimize induced variance yet are time-efficient. Purpose: The goal of this study was to quantify the within-day variance of two commonly reported, sub-maximal tasks utilised for low back EMG normalization: one collected with a high degree of meticulousness, and the other collected in a more rapid manner. Results: Only minimal differences were seen between tasks in the magnitude of within-day variance for EMG amplitude at all recording sites, save the right-side L5 location, which showed a significant difference (p=0.020). For trunk posture, within-day variance for the highly meticulous tasks was significantly higher than for the less-meticulous task (p=0.011). Conclusion: A less meticulous sub-maximal normalization task performed in a standing position was equal or superior to a more meticulously collected task in terms of kinematic task repeatability and within-day EMG variance. These findings are encouraging for field study applications where meticulous methods are not feasible, and provide a time saving strategy for lab studies.