Types and Frequencies of Physical Activity Associated with Physical Fitness in Chinese Children and Adolescents: A National Cross-Sectional Study

<b>Background:</b> Rising sedentary behavior and declining physical activity (PA) among youth are major public health concerns. Evidence on how different PA types affect fitness in Chinese children is limited. PA indicators were classified according to the Global Matrix 4.0, an international framework for benchmarking PA in children and adolescents. <b>Objective:</b> To identify which PA types and frequencies, based on the Global Matrix 4.0, are most associated with physical fitness in Chinese youth. <b>Methods:</b> Data from 102,942 children aged 9-18 were analyzed. Descriptive statistics summarized demographics, PA levels, and physical fitness rates. Chi-square tests assessed group differences. Binary logistic regression examined associations between PA and physical fitness, adjusting for gender, age, school level, parental education, and urban-rural residence, with cluster-robust standard errors at the school level. <b>Results:</b> Higher frequencies of moderate-to-vigorous physical activity (MVPA), muscle-strengthening exercise (MSE), and organized sports and physical activity (OSPA) were significantly associated with better fitness (<i>p</i> < 0.001). OSPA (OR = 1.23) and MSE (OR = 1.21) showed the strongest associations. Sedentary behavior was negatively associated with fitness (<i>p</i> < 0.001). <b>Conclusions:</b> Regular engagement in MVPA, MSE, and OSPA, alongside reduced sedentary time, promotes physical fitness among Chinese children and adolescents. Policies should support diverse and consistent PA participation.