In the USA, the most referenced article on fluid replacement
(before, during, after) is the position stand from the American
College of Sports Medicine. http://tinyurl.com/23gvbq5 (pdf
file, 196 KB) There are numerous websites that reference that
information, admittedly aimed more at runners, but still good
information. In that article is the recommendation to replace
fluids at the rate of sweating, for optimal performance
(avoiding >2% body weight loss from water deficit). "The goal of
drinking during exercise is to prevent excessive dehydration
(>2% BW loss from water deficit) and excessive changes in
electrolyte balance to avert compromised exercise performance.
The amount and rate of fluid replacement depends upon the
individual sweating rate, exercise duration, and opportunities
to drink. Individuals should periodically drink (as
opportunities allow) during exercise, if it is expected they
will become excessively dehydrated. Care should be taken in
determining fluid replacement rates, particularly in pro