The warm sea off Honduras, the buoyancy provided by the wreckage the woman was clinging to and the insulating layer of fat covering her body will all have contributed to her survival in the water for six days.
In a colder sea, no matter how hard she shivered or exercised, she would have rapidly become hypothermic as her body temperature dropped and she would have lost consciousness and drowned. But in a warmer sea of 25C or above it is possible to stabilise the body temperature by shivering.
Dr Tipton, a reader in applied physiology at the University of Portsmouth and head of the environmental medicine unit at the Institute of Naval Medicine, said: "To survive for that length of time is right on the limit of what is possible, both in terms of heat loss and being without fresh water or food."
Even in a warm sea, after several days without food or water, the body will run out of fuel to keep the muscles working. The length of time is determined by the effort needed to stay afloat and the layer of insulating fat keeping the body warm.
Dr Tipton said: "It is not the same as being tired or exhausted. It is a case of there being no more fuel for the muscles. It like the marathon runners you see whose legs go wobbly at the end of a race because they have just run out of sugar."
He added: "The fatter someone is the smaller the amount of heat they need to generate to maintain their temperature. Having something to keep her afloat would have helped, too. If she had been swimming she would have become exhausted much quicker."