Comparison of Tasks to Determine Maximum Voluntary Contraction of Lumbar Muscles in Physically Active Men: Cross-Sectional Study

Introduction: Surface electromyography (sEMG) is commonly used to assess muscle activity; however, accurate interpretation requires normalization. The maximal voluntary contraction (MVC) is the most widely applied approach for this purpose although selecting an appropriate task to achieve MVC, particularly in the posterior muscles of lower back, remains challenging. This study aimed to compare tasks used to apply manual resistance for determining MVC in physically active men with the goal of enhancing the reliability of sEMG normalization in spine-related research.
Materials and Methods: Eight young physically active men participated in this study. The longissimus, iliocostalis, and multifidus muscle activities were assessed using sEMG. Manual resistance for achieving MVC was applied during prone trunk extension, declined trunk extension, and the arch test. One-way analysis of variance (ANOVA), Bonferroni post-hoc test, and Cohen’s effect size were used for data analysis.
Results: The ANOVA results revealed significant differences among MVC tasks for the longissimus, iliocostalis, and multifidus muscles (P < 0.05). Bonferroni's post-hoc analysis showed that prone trunk extension exhibited significantly different MVCs from other tasks for the longissimus. Additionally, for the multifidus and iliocostalis muscles, MVC during the prone trunk extension task was significantly different from that of the arch task (P < 0.05). Cohen's effect size indicated that prone trunk extension, for the longissimus and multifidus, had a much greater effect than other tasks. However, in the iliocostalis muscle, the declined trunk extension and prone trunk extension tasks showed similar results, with no significant difference between them.
Conclusion: Manual resistance against prone trunk extension apparently emerges as the most effective task for achieving MVC in longissimus, iliocostalis, and multifidus muscles in the lumbar spine, highlighting its reliability for normalizing sEMG in physically active men.