We saw a fell race in Andorra at the weekend. It was 170 km with 12,000 metres of ascent in 37 hours max. One of the front runners had cramp, but we were travelling with a top 'physio'; Helen Millson, who at one time wielded the magic sponge for the Springboks.
http://www.youtube.com/watch?v=LK9uH1tHVik