Abstract
This study analyzed associations between physical activity (PA), sedentary behaviors (SB), sleep, and mental health indicators in young adults during the COVID-19 lockdown (15 January-19 April 2021). The participants were 549 Portuguese university students (18-30 years, 57.7% male). Mental health was assessed using the DASS-21 for depression, anxiety, stress, and DASS-21 total score (DASSt). Physical activity (vigorous, moderate, walking) was measured with the IPAQ, while SB (e.g., sitting, screen time) and sleep were evaluated using self-reported measures and the Pittsburgh Sleep Quality Index (PSQI). Multiple linear regressions showed that sleep quality (β = 2.116), sitting time (ST; β = 0.451), vigorous PA (VPA; β = -0.005), and computer use for work/study (β = 0.444) were significantly associated with overall mental health, DASSt (R(2) = 0.358). Sleep quality, sitting, and VPA were also linked to depression (R(2) = 0.308), anxiety (R(2) = 0.275), and stress (R(2) = 0.338). Computer use for work/study was additionally associated with anxiety and stress. Overall, poor sleep quality, increased sitting, and computer use for work/study, alongside lower VPA, showed significant associations with poorer mental health outcomes. These findings highlight the importance of sleep, PA, and limiting sedentary behaviors, particularly during lockdowns, in mitigating mental health issues among Portuguese young adults.