Physical activity is not associated with feelings of mental energy and fatigue after being sedentary for 8 hours or more

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The objective of this study was to examine the associations between physical activity (PA) and sedentary behavior (SB) on feelings of: 1) mental energy (ME), 2) physical energy (PE), 3) mental fatigue (MF) and 4) physical fatigue (PF) in participants who report sitting for less than 8 h (<8 h) compared to those who report sitting for greater than 8 h (>8 h) during the initial lockdown phase of the COVID-19 pandemic. Using a longitudinal study design, we measured PA and SB using the International Physical Activity Questionnaire-Short Form (IPAQ0SF) and feelings of ME, PE, MF, PF and fatigue using the Trait-State Mental and Physical Energy and Fatigue Questionnaire. Participants were then split into 2 groups, <8hr and >8hr. A series of step-wise regression models were used controlling for demographic factors and other lifestyle factors (e.g. sleep, mental workload, diet). Among the 473 participants in the <8hr group, PA was associated with increased PE and ME and decreased MF. However, of the 366 participants in the >8hr group PA was only associated with increased PE and decreased PF. We found PA was not significantly associated with ME and MF for participants who reported sitting >8hr. Our results suggest that sitting for >8hr may negate the positive benefits of PA on ME and MF. We recommend that individuals with low levels of ME and MF and who sit for >8hr to prioritize reducing their sitting time. For individuals with low levels of PE or PF, increasing PA is likely beneficial regardless of SB.