Differences between meeting 24-hour movement guidelines and physical fitness levels among Japanese elementary school children

Current physical fitness levels in Japanese children are lower than that in the 1980s. Investigating the specific relationship between adherence to 24-hour movement guidelines (24-h MG, MVPA: moderate-to-vigorous physical activity; ScT: screen time; Sleep: sleep duration) and physical fitness is crucial to improve childrens fitness levels. Overall physical fitness and eight physical fitness component scores (handgrip strength, sit-up, sit-and-reach, repeated side jump, 20-meter shuttle run, 50-meter sprint, standing long jump, and softball throw) were measured using standardized tests in Japanese elementary schools. Associations between compliance with 24-h MG, overall physical fitness, and each physical fitness component score were analyzed by analysis of covariance. A total of 307 participants (41.4% male) were included in the analysis. Overall fitness scores were significantly higher in children who met only MVPA (P < 0.01), MVPA and ScT (P < 0.01), MVPA and Sleep (P < 0.001), and all three criteria (P < 0.05), than in those who did not. Children meeting only MVPA, MVPA and ScT, and MVPA and Sleep criteria, had higher scores for physical fitness components than those who did not. Children who met one or both of ScT and Sleep criteria, did not differ significantly for overall fitness or its components scores compared to those who did not meet. Handgrip strength and flexibility were not associated with any 24-h MG pattern. Furthermore, compliance with MVPA combined with other behaviors (ScT and Sleep) demonstrated a trend towards greater overall fitness, muscle strength in lower extremities, cardiorespiratory fitness, agility, and dexterity.