This week, Catriona tells us about the health dangers of sitting, and new research giving the good news that any alternative form of activity is beneficial; and Chris looks into why bats harbour such dangerous viruses, with a new study that predicts high virulence for viruses from them and a surprising other order of mammals.Blodgett et al. 2023. Device-measured physical activity and cardiometabolic health: the Prospective Physical Activity, Sitting, and Sleep (ProPASS) consortium. https://doi.org/10.1093/eurheartj/ehad717Brook et al. 2023. Reservoir host immunology and life history shape virulence evolution in zoonotic viruses. https://doi.org/10.1371/journal.pbio.3002268