Disclosing Core Strength: Reliability and Correlations Before and After COVID-19 Pandemic in Plank and Sit-Ups Tests

Abstract

Abstract Objective: to assess the reliability of the core "Plank" test, investigate its correlation with abdominal resistance strength, and examine its longitudinal association before and after the COVID-19 pandemic in schoolchildren during the transition to adolescence. Methods: The initial sample included 221 students aged 6 to 11 years in 2018 (58.8% of boys). These same students were reevaluated between May and June 2023, at ages 11 to 16 years. The baseline assessments encompassed the Plank Isometric Test and the Abdominal Sit-up (Dynamic Strength test). Due to resource limitations, only the Plank test was conducted during the post-pandemic evaluation. To verify the reliability and reproducibility of the plank test, the two-way intraclass correlation coefficient (ICC) was used, also correlation coefficients (r) were calculated. Results: The final sample comprised 130 boys and 91 girls, and the Plank test demonstrated high reliability for both genders, with ICC ranging from 0.623 to 0.869 for boys and 0.695 to 0.901 for girls, as well as high Cronbach's Alpha (α) values, indicating internal consistency. The results revealed significant correlations between the Plank Test and other physical fitness variables for both boys and girls. The Sit-Up test showed moderate positive correlations with the follow-up Plank Test in girls, while in boys, the correlation was weak and negative in the baseline evaluation but became moderate and positive when adjusted for age. Conclusion: The isometric plank strength test is highly reliable in children aged 6 to 16 years and can be used as an alternative measure to assess core strength in school-aged children. Additionally, there was a significant and strong relationship between the Plank Test and the abdominal sit-up strength-resistance test, which provides valuable insights for fitness assessment in this age group.