Objectives. This study aimed to investigate cross-lagged associations in motor competence, cardiorespiratory fitness, muscular fitness and accelerometer-based moderate-to-vigorous physical activity (MVPA) engagement. Design. One-year prospective follow-up study. Method. A sample was 491 (275 girls;M at baseline = 11.27, SD = .32) Finnish physical education students. Students’ motor competence was assessed by 1) two-legged jumping from side to side test, 2) throwing-catching combination test and 3) 5-leaps test. Their cardiorespiratory fitness was analyzed by a 20-meter shuttle run test and muscular fitness by curl-up and push-up tests. Additionally, students’ MVPA was measured objectively by hip-worn accelerometers. Results. Results demonstrated that: 1) cardiorespiratory fitness measured at Grade 5 was the only significant predictor of later MVPA and this association appeared only in the boys’ group, 2) MVPA assessed at Grade 5 significantly predicted cardiorespiratory fitness in the girls’ group, 3) cardiorespiratory fitness collected at Grade 5 associated with muscular fitness, locomotor and stability skills in both girls and boys, and 4) locomotor skills measured at Grade 5 predicted significantly muscular fitness, locomotor and manipulative skills in both sex groups. Conclusions. Elementary school years are important in providing students with experiences in physical activity (PA) which leads to improvements s in cardiorespiratory health. Additionally, this study showed that cardiorespiratory fitness collected at Grade 5 associated with later muscular fitness, and locomotor and stability skills in both sex groups. These findings are noteworthy because muscular fitness in youth has several health-related benefits and motor competence in childhood and adolescence has positive association with later PA engagement.