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How much and what types of fluids should marathon runners drink during a race? CJSM offers guidelines on the best approaches to fluid replacement according to updated recommendations by the International Marathon Medical Directors Association (IMMDA).
Newswise — How much and what types of fluids should marathon runners drink during a race? Rather than hard-and-fast rules, drinking when thirsty and drinking the types of fluids the runner has a taste for are the best approaches to fluid replacement in most situations, according to updated recommendations by the International Marathon Medical Directors Association (IMMDA).
"Drinking to thirst is the body’s dynamic physiologic fluid calculator and in most cases will protect athletes from the hazards of both over and underdrinking," according to the IMMDA Position Statement. The new statement appears in the July/August issue of the Clinical Journal of Sport Medicine.
In developing the recommendations, the IMMDA reviewed current scientific evidence on the often-complex physiologic processes governing fluid balance. Past guidelines for fluid replacement during prolonged exercise have recommended estimating fluid losses due to sweating, measuring changes in body weight during the race, or following prescribed amounts of fluids. However, these "static" approaches don't consider the "dynamic" processes governing fluid balance—not to mention the wide range of shapes, sizes and speeds seen in today's marathon runners.
The key recommendation is to drink when thirsty, and to avoid drinking when not thirsty. This will prevent dehydration due to fluid losses while exercising, while also avoiding the risk of dangerously low sodium levels caused by excessive fluids. Studies have shown that thirst is a better guide to maintaining fluid balance than other approaches, such as estimated fluid losses or weight loss.
Runners should also follow their body's cues regarding what type of fluids to drink—plain water or sports drinks, which provide sodium and other minerals. During a race, sodium levels may rise because the body loses more water than salt through sweat. When this happens, the body craves water to maintain normal salt levels in the blood. As sodium levels become diluted or when the marathon is over, the runner may develop a taste for sodium-containing items to maintain sodium levels or to restore water in the circulation that was lost through sweat.
There are some special situations in which recommendations differ, particularly in very hot or cold conditions or in older athletes. Although weight loss is not a good guide to fluid replacement, runners who lose more than four percent of body weight during a race—or those who gain any weight—need medical evaluation.
The IMMDA doesn't discourage runners from using fluid calculators or charts as a guide to estimating fluid needs—however, they should always defer to the body's "physiologic cues" to increase or decrease fluid consumption. "Clinicians and scientists must resist handing out unrealistic 'blanket advice' to individuals seeking simple answers, but rather should encourage athletes to explore, understand and be flexible toward their own needs," the IMMDA Position Statement concludes. "By providing guidelines and advice on how to appropriately understand individual fluid replacement needs, we can eliminate future fluid balance problems by avoiding the temptation to generalize one rule for every situation and every athlete."
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