Sleep quality and physical fitness among Chinese adolescents: a multilevel cross-sectional study

Background Sleep quality is an important component of adolescent health, but its association with physical fitness remains insufficiently understood. This study examined the association between sleep quality and physical fitness among Chinese adolescents. Methods This school-based cross-sectional study included 5,018 adolescents from 18 schools in six Chinese cities. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI). The Physical Fitness Index (PFI) was the primary outcome, and estimated VO₂max was the secondary outcome. School-level random-intercept models adjusted for age, sex, school stage, BMI, socioeconomic status, and screen time. Sensitivity analyses examined school-clustered standard errors and exploratory models incorporating random intercepts for school and class within school. Results Higher PSQI scores were associated with modestly lower PFI in the fully adjusted school-only model ( β = −0.049, 95% CI: −0.079 to −0.019, P = 0.002). The PFI association remained significant with school-clustered standard errors (95% CI: −0.086 to −0.012, P = 0.013) and in the exploratory school-and-class model ( β = −0.040, 95% CI: −0.068 to −0.012, P = 0.005). For estimated VO₂max, the association was non-significant in the fully adjusted school-only model ( β = −0.036, 95% CI: −0.082–0.010, P = 0.125), but significant in the exploratory school-and-class model ( β = −0.049, 95% CI: −0.092 to −0.005, P = 0.030), indicating sensitivity to the clustering specification. Conclusions Poorer sleep quality was modestly associated with lower PFI among Chinese adolescents. Longitudinal and intervention studies are needed to clarify temporal relationships and evaluate potential implications for health monitoring and fitness promotion.