WHO, WHAT, WHY?
The Magazine answers...
David Blaine has just finished his latest stunt - hanging upside down for three days. But what are the effects on the body of upending yourself and can it be dangerous?
Why it's a bad idea to be upside down is all about evolution.
Humans have evolved under the influence of a lifestyle that sees them one way up for the vast majority of every day.
As a result it makes sense that the way the blood is pumped around the body naturally relies on gravity to help.
Putting yourself the wrong way up means it is harder to get blood to the lower limbs and that blood is not easily returned from the head and upper body, with potentially disastrous effects.
Dr Paul Ford, senior lecturer in exercise physiology at the University of East London, cannot think of any type of sportsman who spends prolonged periods of time upside down.
Trapeze artists, rock climbers and bungee jumpers find themselves upside down, but it is rarely for more than a few minutes.
"The main thing is going to be the gravitational effect on blood flow. Normally the heart is supported by the effect of gravity," says Dr Ford.
When blood is being pumped to your feet, gravity helps take it on its way. To get blood to your head your body has evolved to pump harder.
But while there are muscles that help get the blood back from the legs, the brain doesn't have these same muscles. So it doesn't take long before blood begins to pool in places where it shouldn't, like the lungs and head.
"The major concern is about the control of the vascular system," says Professor Ashley Grossman, of Barts Medical School, part of Queen Mary, University of London.