Association Between Frequency of Muscle-Strengthening Exercise and Depression Symptoms Among Middle and High School Students: Cross-Sectional Survey Study

Background: Existing literature on the association between the frequency of muscle -strengthening exercise (MSE) and depression among adolescents is limited and contradictory. Objective: This study aimed to elucidate the association of MSE frequency with depression symptoms among middle and high school students in China. Methods: A total of 27,070 students in grades 7-12 from 376 middle and high schools were surveyed using an anonymous self-administered questionnaire between April and June 2022. Information on engaging in MSE was self -reported, and depression symptoms were assessed using the Patient Health Questionnaire -9 (PHQ-9). Poisson regression was used to examine the association between MSE frequency and depression symptoms. Results: Among the 27,006 eligible students, 51.6% (n=13,933) were boys, and the mean age was 15.6 (SD 1.7) years. The overall prevalence of meeting MSE recommendations (ie, engaging in MSE >= 3 days/week) was 34.6% (95% CI 32.6%-36.6%; n=9145); the prevalence was higher in boys (43.8%, 95% CI 41.8%-45.8%; 6067/13,933) than in girls (24.3%, 95% CI 22%-26.6%; 3078/13,073; P<.001). A total of 5882 (21.8%) students reported having depression symptoms. After adjustment for sociodemographic status, lifestyle factors, academic performance, and experience of physical fighting, compared to students who did not engage in MSE, the prevalence ratios (PRs) for depression symptoms were 0.98 (95% CI 0.97-0.99) for those engaging in MSE once a week, 0.95 (95% CI 0.93-0.97) for 2 days/week, 0.93 (95% CI 0.90-0.96) for 3 days/week, 0.90 (95% CI 0.87-0.94) for 4 days/week, 0.88 (95% CI 0.84-0.93) for 5 days/week, 0.86 (95% CI 0.81-0.92) for 6 days/week, and 0.84 (95% CI 0.78-0.90) for 7 days/week, respectively. Conclusions: The overall prevalence of meeting MSE recommendations among Chinese adolescents is low. The frequency of MSE was inversely associated with depression symptoms.