Bout Characteristics of MVPA and its Relationship with Physical Fitness in Children and Adolescents

Objective: To explore the bout characteristics of moderate-to-vigorous physical activity(MVPA) and its relationship with physical fitness in children and adolescents. Methods: A total of 360 4th and 8th grade students in three districts of Shanghai were recruited in this study. According to the requirements of the National Students' Physical Health Standards(Revised in 2014), the physical fitness of children and adolescents were assessed. Total MVPA, sporadic bouts(0~4 min) of MVPA, short bouts(5~9 min)of MVPA, and medium-to-long bouts(≥10 min) of MVPA were measured over 7 days by using accelerometers. The valid sample was set as wearing the accelerometer for at least 10 hours per day and at least 4 days per week(3 weekdays and 1 weekend day).Results: A total of 407 participants were included in statistical analysis(185 boys, 45.5%), and 223 of them were 4th grade students(54.8%). Their BMI median was 18.6 kg/m², and only 6.6% of them were meeting the international recommendations for MVPA.Sporadic-bouts MVPA accounted for the largest proportion(59.9%). Medium-to-long-bouts MVPA proportion in boys(24.4%) was significantly higher than that of girls(12.3%)(P<0.05), while the proportion of MVPA in sporadic-bouts and short-bouts was opposite(P<0.05, P=0.033). Sporadic-bouts MVPA proportion in 4thgrade students(65.4%) was significantly higher than that of 8th grade students(51.1%)(P<0.05), while the proportion of short-and medium-to-long-bouts MVPA had opposite trend(P<0.05).After adjusting for confounding factors(gender, age, BMI, grade and valid wearing time), the results of the binary logistic regression showed that there was a positive correlation between sporadic-bouts MVPA and good-excellent physical fitness standard. For every1 min/day increase, the odds ratio(OR) was increased by 8%(95%CI: 4%, 13%) compared with the ratio of good-excellent physical fitness standard and not good-excellent physical health standard. In the 4thgrade students, the total MVPA, sporadic-bouts MVPA and short-bouts MVPA were positively correlated with the good-excellent grade of physical fitness standard. Among 8thgraders, only sporadic-bouts MVPA was positively correlated with the rate of good-excellent physical fitness standards. Conclusions: The proportion of children and adolescents meeting the international recommendations for MVPA is extremely low. Sporadic-bouts MVPA is the main component of MVPA in children and adolescents, which is positively correlated with physical fitness. It is suggested that the characteristics of physical activity of children and adolescents and the characteristics of gender differences should be fully considered, and personalized and targeted physical activity promotion programs should be formulated.