PurposeWhile there are some studies on sleep and physical activity, little is known regarding the associations between sleep and sedentary behavior. This study investigated the associations between sleep, sedentary behavior, and physical activity among young adults. MethodsCross-sectional data from 124 undergraduate students were included in the analysis (age=21±1 years). Both accelerometer-based and self-report assessments of sleep were included; physical activity and sedentary behavior were assessed by accelerometers. Participants were asked to fill out sleep questionnaires and wear accelerometers for 7 days. Pearson correlations, partial correlations, and analysis of covariance (ANCOVA) analyses were performed to investigate the relationships between sleep, sedentary behavior, and physical activity. ResultsAfter adjusting for age, gender, percent body fat, educational level, and monthly allowance, prolonged sedentary time was correlated with a shorter sleep onset latency (r=-0.19, p=0.04), shorter time in bed (r=-0.43, p<0.001), and shorter sleep duration (r=-0.38, p<0.001). Moderate-to-vigorous physical activity (MVPA) was positively correlated with sleep onset latency (r=0.43, p<0.001). Sedentary behavior and MVPA were not correlated with sleep quality or daytime sleepiness. After further categorizing sleep duration into three subgroups, individuals with ≤6 hours (p<0.001) of sleep spent more time being sedentary than did those with 6-7 hours (p<0.001) and ≥7 hours (p=0.007) of sleep. Individuals with 6-7 hours of sleep had a higher level of MVPA than did those with ≥7 hours of sleep. ConclusionImproving the duration of sleep may be a viable approach to help reduce sedentary behavior among young adults. Future studies with longitudinal designs are needed to further investigate the directionality of these associations and their potential mediators and moderators.

Purpose To compare physical activity and sedentary behavior between four commonly used subjective and objective measures: the 7-day Physical Activity Recall (7DPAR), International Physical Activity Questionnaire (IPAQ), pedometer, and accelerometer. Methods A total of 130 college students completed four measures for the same 7 days. Body composition was measured using a bioelectric impedance analyzer. Wilcoxon signed rank tests and Spearman correlations were performed to compare estimates between activity measures. The Spearman correlations between different activity measures were further examined separately for the higher and the lower body fat groups. Results Compared with accelerometer-derived data, both the 7DPAR and the IPAQ overestimated light physical activity (P < 0.001) while underestimated sedentary behavior (P < 0.001). Across comparisons, the highest correlation was found between accelerometers and pedometers on steps/day (r = 0.72, P < 0.001). The 7DPAR and the IPAQ were correlated with each other for all physical activity variables and sedentary behavior (r = 0.37-0.45). There were low correlations (r = 0.20-0.47) between the 7DPAR, the IPAQ, and accelerometers in sedentary behavior, light physical activity, and vigorous physical activity. Higher correlations between different activity modalities were observed among individuals with lower body fat (r = 0.41-0.80) than among those with higher body fat (r = 0.31-0.65). Conclusions The 7DPAR and the IPAQ yielded comparable estimation of moderate physical activity relative to accelerometers. There were significant differences in sedentary time across activity measures. Body compositions should be considered when comparing the estimates of activity levels between subjective and objective instruments.