Long-haul flying increases your risk of developing a dangerous blood clot called Deep Vein Thrombosis.
This medical condition (known as DVT) is caused by sitting in the same position for long periods.
See also: Expert advice: Flying long-haul
To help reduce the risk it's important to drink plenty of water and avoid alcohol, as well as wear loose-fitting clothes. DVT is rare, but it's wise to take sensible precautions.
"Where possible it's good to get up regularly and stretch your legs," says Will Beck, Flight Centre's head of airfare expertise. "There is normally space at the back or front of the cabin. Request an aisle seat, so getting out is as easy as possible. There are also exercises you can do in your seat, and most airlines include some useful exercises in the in-flight magazine."