In the 1960’s the scientific literature suggested that the dehydration caused by a 3-4%
decrease in body weight was insignificant and it was only until greater than 4% of body
weight was lost that there was a danger to health [15]. Today it is well acknowledged that a
fluid deficit of this kind is not only detrimental to performance but also a hazard to health.
In its most recent position stand [13], the Australian College of Sports Medicine recommends
that ‘During exercise, athletes should start drinking early and at regular intervals in an
attempt to consume fluids at a rate sufficient to replace all the water lost through sweating’.
In 2000, the National Athletic Trainers Association also published a position statement that
aimed to ‘provide useful recommendations to optimise fluid replacement for athletes’. The
statement identified individual variation in fluid intakes due to differences in sweating rates,
environmental conditions, exercise duration, exercise intensity as well as the sport dynamics
[16]. Further recommendations from the statement were that ‘fluid replacement should
approximate sweat and urine losses, and at least maintain hydration at less than 2% body
weight reduction’ [16]. This highlights the evolution of scientific findings in the last 30 years
in this area, and the challenges in developing practical individual guidelines for ultra
endurance athletes.