Measures aiming at containing the Coronavirus disease 2019 (COVID-19) include isolation, social distancing, and quarantine. Quarantine and other lockdown instruments show promise in reducing the number of COVID-19 infections and deaths. It is reasonable to assume that lockdown leads to reduced levels of physical activity in the general population. Potential detrimental health effects of lockdown, such as psychological distress and physical inactivity induced maladaptations must be addressed. The current review summarizes harmful effects of limited physical activity on mental and physical health due to social distancing and quarantine and highlights the effects of simple physical activity regimes counteracting these detrimental effects, with a special emphasis on acute effects.