Objective To explore the associations of volume and accumulation patterns (duration of sedentary bouts and breaks) of sedentary behavior with physical fitness among elementary school students.

Methods From September to October 2023, a convenience sampling method was adopted to select 605 elementary school students (grades 1 to 5) from Wuhan city, Hubei province and Jinhua city, Zhejiang province. Accelerometers were used to measure the sedentary volume and the duration of sedentary bouts and breaks. The physical fitness were scored according to the National Student Physical Health Standards (Revised in 2014). Binary logistic regression was employed to examine the associations of volume and accumulation patterns of sedentary behavior with physical fitness.

Results The surveyed students spent 65.2% of the classroom time in sedentary behavior. The highest proportions were observed for the sedentary bouts of 1–19 min (47.3%) and breaks of 1–4 min (17.7%) in class. In the Q4 group with the highest proportions of sedentary bouts lasting 5–9 min and ≥ 20 min , the odds of failing to achieve good or excellent physical fitness were 0.451 times (OR = 0.451, 95%CI: 0.247–0.823) and 2.16 times (OR = 2.16, 95%CI: 1.043–4.474), respectively, those of the Q1 group. No statistically significant associations were observed between the proportion of sedentary volume or sedentary break duration and failure to achieve good or excellent physical fitness. Further analysis of physical fitness factors revealed that the odds of failure to achieve good or excellent physical fitness in the Q4 group with the highest sedentary volume proportion were 3.673 times that of the Q1 group (OR = 3.673, 95%CI: 1.085–12.434). For the sedentary bouts of 5–9 min, the Q4 group exhibited lower odds of poor speed ability (OR=0.48, 95%CI: 0.262–0.881) and strength ability (OR = 0.378, 95%CI: 0.162–0.882) than the Q1 group. In contrast, the Q4 group with the highest proportion of sedentary bouts ≥ 20 min showed 4.969 times higher odds of poor body composition (OR = 4.969, 95%CI: 1.406–17.560) and 2.717 times higher odds of poor strength ability (OR = 2.717, 95%CI: 1.120–6.593) than the Q1 group.

Conclusions The sedentary behavior of elementary school students presents a fragmented pattern characterized by short terms and frequent breaks. Reducing the duration of sedentary bouts in class may be more important for the fitness of elementary school students than reducing the volume of sedentary behavior. According to the body composition, it is necessary to reduce the volume of sedentary behavior and shorten the duration of sedentary bouts in class. The quality of strength and speed can be improved by shortening the duration of sedentary bouts in class.