Strength in Decline? Strength Performance’s Secular Trends of Italian Middle School Children

It is well known that there is a concerning decline in overall physical fitness (PF) levels among youth. Despite these, studies on trends in muscle strength (MS) yield conflicting results. Moreover, continuous temporal data focusing on children and adolescents are lacking, with limited consideration of factors such as body mass and maturity timing in MS trend analyses. This study addressed these gaps by examining the secular trends in MS performance among Italian school children while considering the influence of body mass index (BMI) z-score and peak height velocity (PHV). A repeated cross-sectional study spanning 21 years (1988–2009) was conducted, involving 3,761 Italian children aged 11–13 years. Physical fitness assessments were conducted annually and secular trends were analyzed using weighted least squares regression, adjusting for BMI z-score and PHV. Sit-up performance showed a steady trend (trend [95% confidence interval]: −0.72 [−0.73 to −0.71]; −4.76% [−4.79 to −4.73]; −0.16 effect size [ES] [−0.17 to −0.15]), while push-up performance showed a small-to-moderate decline (−1.01 [−1.03 to −0.99]; −5.77% [−5.81 to −5.73]; −0.26 ES [−0.27 to −0.25]). Girls exhibited consistent declines, however, trends differed among boys depending on the test used. This study contributes valuable insights into secular trends in MS among Italian school children, underscoring the need for gender-sensitive approaches to promoting physical activity and the importance of standardized assessments to accurately monitor fitness trends. Addressing these disparities is critical for the creation of interventions aimed at reducing the economic burden associated with low PF levels and improving overall public health.