Physical Activity and Sedentary Behaviour in People with Long COVID: A Follow-Up from 12 to 18 Months After Discharge

<b>Background/Objectives</b>: Long-term effects of post-COVID-19 on several health outcomes remain unclear. We assessed PA and sedentary behaviour changes and explored behaviour-change factors twelve months post-COVID-19 in people with and without Long COVID. <b>Methods</b>: A prospective cohort study followed people treated for COVID-19 in different settings (home, hospital ward, intensive care unit) from twelve months to eighteen months post-COVID-19. Participants with and without Long COVID were identified. PA (Light PA-LPA, Moderate-to-Vigorous PA-MVPA, Steps·day^-1), sedentary time, functional capacity (six-minute walk test-6MWT), muscle strength (quadriceps maximal voluntary contraction-QMVC), dyspnoea (modified Medical Research Council scale-mMRC), fatigue, symptoms of anxiety and depression, and health-related quality of life-HRQoL were assessed. <b>Results</b>: Among 148 participants (58 ± 15 years, 54% male), 101 had Long COVID. All remained physically inactive. People with Long COVID significantly increased LPA (LPA_LongCOVID +28 [1; 55] min·day^-1; LPA_Controls +6 [-32; 45] min·day^-1), and decreased MVPA (MVPA_LongCOVID -4 [-7; -2] min·day^-1; MVPA_Controls -4 [-8; 1] min·day^-1) and sedentarism (Sedentarism_LongCOVID -47 [-89; -4] min·day^-1; Sedentarism_Controls -30 [-88; 28] min·day^-1). At eighteen months, higher proportions of individuals with Long COVID had impaired 6MWT (17% vs. 0%), reduced QMVC (25% vs. 6%), dyspnoea (24% vs. 0%), fatigue (67% vs. 13%), symptoms of anxiety (47% vs. 9%) and depression (26% vs. 0%) as well as poor HRQoL (50% vs. 6%). PA and sedentary behaviour changes at eighteen months were associated with dyspnoea and impaired QMVC at twelve months (LPA: mMRC ≥ 2: -41.56 [-129.30; 46.00] min·day^-1, Steps·day^-1: mMRC: -416.13 [-1223.83; 391.57]; QMVC ≤ 70% predicted: -1251.39 [-2661.69; 158.91], Sedentarism: mMRC ≥ 2: +47.21 [-90.57; 184.99] min·day^-1; 0.24 ≤ R² ≤ 0.32). <b>Conclusions</b>: PA and sedentary behaviour remain altered long after COVID-19, with people with Long COVID adjusting to fit lower PA levels, possibly driven by physical limitations and symptoms. Dyspnoea and muscle weakness may influence PA and sedentary behaviour.