Is Social Jetlag Associated With Physical Fitness Among Spanish Adolescents? Insights From the EHDLA Study

Background: The misalignment of sleeping times during weekdays/weekends (i.e., social jetlag) is particularly common among adolescents and plausibly associated with their physical fitness. However, literature on this topic is scarce. Therefore, this study aimed to investigate the association between social jetlag and physical fitness in Spanish adolescents. Methods: A secondary analysis was conducted on cross-sectional data from the Eating Healthy and Daily Life Activities (EHDLA) study among 812 adolescents (54.9% girls) aged 12–17 years from the Valle de Ricote (Region of Murcia, Spain). Social jetlag was calculated from self-reported data on bedtimes and wake times for weekdays and weekends. Physical fitness was evaluated with the Assessing the Levels of PHysical Activity and Fitness (ALPHA-FIT) for children and adolescents and included cardiorespiratory fitness, muscular fitness, speed agility, and flexibility. Results: The analysis revealed significant negative associations between worse social jetlag and detrimental overall physical fitness (unstandardized beta coefficient [B] = −0.06, 95% confidence interval [CI]: −0.09, −0.02; p = 0.002), cardiorespiratory fitness (B = −1.28; 95% CI −2.22, −0.34; p = 0.008), and lower body muscular fitness (B = −2.01; 95% CI −3.90, −0.12; p = 0.038) after the adjustment for potential covariates (age, sex, socioeconomic status, physical activity level, sedentary behavior, nocturnal sleep duration, energy intake, and body mass index). In contrast with other fitness components, a significant positive association was identified between social jetlag and speed agility (B = 0.07; 95% CI 0.00, 0.14; p = 0.049). Conclusions: In adolescents, social jetlag is significantly linked to poorer physical fitness, especially for cardiorespiratory fitness and lower-body muscular fitness. Maintaining regular and well-synchronized sleep could be crucial for optimizing physical health and preventing the decline of physical fitness during adolescence.