When we sit in some senses, our bodies go to sleep. It’s striking how little we’re doing when we are in our seats, Dunstan says. There is virtually nothing going on in the muscles. Why is that so important? Well, muscle is a major metabolically active part of the body and needs to be moving to stay healthy. If we don’t contract our muscles by moving, we struggle to clear glucose and fat out of the bloodstream — major risk markers for heart disease. It’s this lack of muscle activity that also increases the risk of clotting. Richard Beasley, director of the Medical Research Institute of New Zealand, has led two studies into the effect of long periods of sitting on blood clots. He found that sitting at a computer for more than ten hours a day, including two hour stints without standing, trebles your risk of a blood clot. The problem is at least as worrying as the better-known danger from long-haul flights.