A049: Associations Between 24-Hour Accelerometer-Derived Novel Metricswith Health-Related Physical Fitness in Chinese Adolescents

<bold>Background/Purpose:</bold> Time-use estimates are commonly utilized for describing 24-hour movement behaviors. Nonetheless, the average acceleration (AvAcc), intensity gradient (IG) and the most active X minutes (MX metrics) have been proposed as 24-hour movement behaviors novel metrics describing the volume of activity, the intensity distribution and the most active time periods of the 24-h cycle. This cross-sectional study aimed to examine associations between 24-h accelerometer-derived metrics and health-related physical fitness in Chinese adolescents. <bold>Methods:</bold> This study recruited 240 students aged 12-18 (143 males, 97 females) from a middle school in Haizhu District, Guangzhou City. The data collection period was from March to May 2023. Participants wore ActiGraph wGT3X-BT triaxial accelerometers on their non-dominant wrist continuously for 7 days to assess physical activity, with removal allowed only during bathing and swimming. Data were sampled at 1-second intervals with a frequency of 30Hz, with at least 2 school days and 1 weekend day (worn for ≥16 hours per day) considered as valid data. The raw accelerometer data were processed using the GGIR package in R software. Health-related physical fitness was assessed using four FitnessGram tests, which included evaluations of cardiorespiratory fitness, muscular fitness, flexibility, and body composition. Multiple linear regression models were performed to predict the association between 24-h accelerometer-derived metrics and health-related physical fitness after adjusting for age, sex and accelerometer wear time. <bold>Results:</bold> The mean value of average acceleration was 27.94 mg, and the mean value of intensity gradient was -2.20. Among the four fitness indicators, only cardiorespiratory fitness was significantly correlated with intensity gradient (<italic>p</italic> = 0.013, <italic>p</italic> &lt; 0.05), as well as with the most active 1, 2, and 5 min (<italic>p</italic> = 0.042, <italic>p</italic> = 0.034, <italic>p</italic> = 0.017, <italic>p</italic> &lt; 0.05). No significant correlations were found with the other indicators. <bold>Conclusions:</bold> Overall, the novel 24-hour activity metrics play a crucial role in health-related physical fitness, particularly in the relationship between intensity gradient and cardiorespiratory fitness. It is necessary to take measures in the future to improve adolescents' health-related physical fitness by providing activity intensities to enhance cardiorespiratory fitness.