Electromyographic Activation of Flexed Arm Circumference, With or Without Contralateral Opposition

Flexed and tensed arm (FTA) circumference is a fundamental anthropometric measurement for determining the mesomorphic component in somatotype. This study examined the impact of contralateral limb opposition (+OP) on arm circumference measurement and biceps brachii muscle activation. Fifty physically active men and women, mean (22.7 ± 2.9 years), participated in this study. FTA circumference measurements were taken with FTA + OP and without opposition FTA, following ISAK protocols. Additionally, biceps brachii muscle activation was assessed using surface electromyography (sEMG). Significant differences were identified in the flexed and tensed arm circumference (>1%) and in the mesomorphic component between the FTA and FTA + OP conditions (<i>p</i> < 0.001). In addition, contralateral limb opposition resulted in a significant average increase of 39.02% in biceps brachii muscle activation, with variations between 24.57% to 47.46% across the time intervals analyzed (<i>p</i> < 0.05). A moderate correlation was observed between the percentage difference in sEMG and arm circumference during the middle second of contraction (<i>r</i> = 0.418). However, during the first (<i>r</i> = 0.393), third (<i>r</i> = 0.376), and mean (<i>r</i> = 0.385) contraction periods, the correlation was considered weak. Contralateral limb opposition caused greater biceps brachii muscle activation, resulting in an increase in flexed and tensed arm circumference in physically active young adults.