Exploring the optimal rest interval between repeated electromyographic measurements of maximal voluntary isometric...

Maximal voluntary isometric contraction (MVIC) is commonly used to normalize surface electromyography (EMG) data, enabling consistent and meaningful comparisons across muscles and individuals. However, insufficient rest intervals may compromise muscle function during repeated MVICs, potentially reducing EMG reliability. This study aimed to determine the optimal rest interval required for the recovery of lumbopelvic muscle activity following MVIC and whether muscle activity patterns differ across individual muscles under varying rest intervals. Twenty-two healthy young adults performed MVICs of the erector spinae, multifidus, gluteus maximus, rectus femoris, and biceps femoris muscles in standardized positions. Surface EMG was recorded, with rest intervals of 30, 45, 60, and 120 s randomly assigned between trials. Significant time × rest interval interactions were observed for all muscles (p < 0.05), with notable pre-to post-test differences in the 30- and 45-s rest conditions. Effect sizes (η²_p) ranged from 0.37 to 0.55, indicating large effects for the time × rest interval interaction. In contrast, no significant interaction was found between rest interval condition and muscle (F = 0.82, p = 0.63), suggesting consistent activity patterns across muscles. These findings indicate that a rest period of at least 60 s is required to restore lumbopelvic muscle activity to baseline levels after MVIC, thereby enhancing the reliability of EMG-based assessments in both research and clinical settings.