Four months after suffering a heart attack, Sir Ranulph Fiennes has run seven marathons, in seven days on seven continents. What will it do to his body?
Now it is all over for the 59-year-old explorer.
INSIDE SIR RANULPH'S BODY
1 Jet lag will undermine routine
2 Dehydration, particularly in humid Singapore
3 Heart working ever harder
4 Cramps and loss of glycogen to fuel heart
5 Crushed capillaries and stress fractures
6 Torn muscles
He has run a marathon a day. First was Patagonia at the southern-most tip of Chile, then the Falkland Islands, then Sydney, Australia, and on Wednesday he completed a 26-mile run in Singapore.
Next was London, then Cairo and finally, on Sunday, New York.
The schedule was unbelievably gruelling, says sports scientist Dr Craig Sharp, not least because of the effects of jet lag.
The chopping and changing will have hit the body clock hard and undermined exercise routine.
Running at the equivalent of 4am, when metabolism is at its lowest, meant it was "much harder to get going," says Dr Sharp.
At least they vaguely travelled west to east, which is thought to be easier than going the other way.
The three-week rule
Even without the globe-trotting, running seven marathons in as many days is a seriously punishing regime. The unwritten rule is that a runner leaves at least three weeks between marathons.
Every marathon runner hits what's known as the "wall" during a race. Up to this point, the body has been feeding its muscle with stored sugars known as glycogen.
Eventually these run out and stored fats become the fuel. But these are less efficient than sugars; the body must work harder to release them and so the heart pumps faster.
Four months ago Sir Ranulph suffered a heart attack and underwent by-pass surgery.
Ironically, says Dr Sharp, the operation may have helped, by clearing his arteries. That's just as well since Sir Ranulph's heart will not pump as fast as that of someone younger.
The "wall" however, will move forward with each marathon, since the body will not be able to fully replace its sugar stores between races.
A side-effect is that their breath will smell sweet - a by-product of the body burning fat rather than sugar.
WILL HE LOSE MUCH WEIGHT?
Fiennes (above, centre) will probably lose only 3½ kilos, says Craig Sharp
Two kilos of fat; one of glycogen; and 0.5 of fluid
'Remember, he will still be eating lots'
The pounding of feet and strain on muscles will hurt. Mike Stroud has started to "pass blood" in the urine. This will be the haemoglobin from red blood cells caused by the crushing of capillaries in the feet each time they hit the road. (Six out of the seven marathons are on hard surfaces.)
Small muscle tears will hurt and not have time to repair. One to two percent of muscle will be damaged after each race.
Another risk is stress fractures to the bones - tiny cracks in the feet and ankles. These would be "unbelievably painful" to run on.
Yet Sir Ranulph's years of arduous exploring will have built up strong bones, minimising the risk of such an injury, says physiologist Joe Dunbar.
The same goes for potential strains to tendons and inflamed knees, while their feet are probably tough enough to repel blisters. Cramp however, is inevitable - the combination of chronic overuse of muscles and the body's inability to absorb enough minerals.