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Re: ACSM Fluid Recommendations: Replace Sweat, not "Drink as much as you can"

Dear Editor,

The case study described by Dugas and Noakes (2005:39;e38) demonstrates the wide individual variability in sweat losses that occur in athletes, and there is not much doubt this woman was ill advised for her fluid replacement plan. The conclusions of the both the case report and the commentary that follows place the blame for her problem on the 1996 American College of Sports Medicine (ACSM) Fluid Replacement Position Stand, whereas the problem seems to be misapplication of the ACSM advice. The case report does not detail where she got her fluid replacement advice but her previous experiences imply that she was overhydrating during exercise for many years, and she may be a “non-responder” to a hypo-osmotic, overhydrated state.

I have copied the pertinent sections of the ACSM position stand below: From the abstract. “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 (i.e., body weight loss), or consume the maximal amount that can be tolerated.” [I have always interpreted the last half of this statement to mean replace up to sweat losses as outlined in the text, but others may have a different view.]

From the main text. “As such, individuals participating in prolonged intense exercise must rely on strategies such as monitoring body weight loss and ingesting volumes of fluid during exercise at a rate equal to that lost from sweating, i.e., body weight reduction, to ensure complete fluid replacement. This can be accomplished by ingesting beverages that enhance drinking at a rate of one pint of fluid per pound of body weight reduction. While gastrointestinal discomfort has been reported by individuals who have attempted to drink at rates equal to their sweat rates, especially in excess of 1 l - h-1, this response appears to be individual and there is no clear association between the volume of ingested fluid and symptoms of gastrointestinal distress. Further, failure to maintain hydration during exercise by drinking appropriate amounts of fluid may contribute to gastrointestinal symptoms. Therefore, individuals should be encouraged to consume the maximal amount of fluids during exercise that can be tolerated without gastrointestinal discomfort up to a rate equal to that lost from sweating.”

From the conclusion. ”During exercise, fluid and carbohydrate requirements can be met simultaneously by ingesting 600-1200 ml - h-1 of solutions containing 4%-8% carbohydrate. During exercise greater than 1 h, approximately 0.5-0.7 g of sodium per liter of water would be appropriate to replace that lost from sweating.” [The key word in this section is "can," it does not say “should” or even imply that all athletes require 600-1200 ml - h-1.]

It appears that she did not get her advice from the American College of Sports Medicine Fluid Replacement Position Stand as suggested by the authors of the manuscript and the commentary, nor did she or her advisors learn from her past experiences. With a sweat rate of 270 ml/hour and a fluid intake of just over 700 ml/hour, she is either going to urinate large volumes during and immediately after her activity or she will become water intoxicated if her kidneys do not respond with appropriate diuresis. Although the wording in the abstract could be misconstrued to mean “drink as much as you can,” the main text clarifies the recommendation. The recommendation stresses replacing sweat losses as the first choice in fluid replacement during exercise, and not more. While the 600-1200 ml - h-1 is higher than 400-800 ml - h-1 that Noakes recommends, it represents the range around the middle of the population and does not reflect the problems faced by those (including this woman) who sit at the extremes of sweat loss during activity. Even the 400 ml - h-1 from Noakes’ recommendation would have left this woman overhydrated at the end of her activity. To site an example like this from the lower extreme of sweat loss as a failure of the ACSM Fluid Recommendations seems a stretch to me and emphasizes that the wide variation in fluid requirements across the entire athlete population makes it nearly impossible to give a precise recommendation that includes specific fluid volumes. The best advice still remains to “replace most of the sweat losses” as outlined in the ACSM Position Stand. The ACSM Exercise and Fluid Replacement Position Stand is currently in revision and should be published in the near future with updates that reflect changes in the area since 1996.

William O Roberts MD, MS, FACSM Past President, American College of Sports Medicine (I have no financial or advisory ties to any water or sports drink companies. I did receive an honorarium from the Gatorade Company for appearing on an educational film clip regarding exertional heat stroke in 2003.)

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