What fluids should I use before my marathon?

Marathon runners can become dehydrated due to the extreme physical activity. What types of fluids should they consume in order to rehydrate their cells?

When you’re dehydrated, water is the hypotonic solution of choice for speedily moving via osmosis from blood directly into body cells that need rehydration (Tortora & Derrickson, 2006). Marathon runners, however, may need a little more solutes in the solution.

The physical exertion of running can create need of other nutrients for these athletes. Regular sweating and using up of glycogen calls for needs of carbohydrates to maintain blood glucose and salts for proper balance of plasma osmalility (Chen & Zimmerman, 1978). Sports drinks can offer an answer for proper running, but too many solutes in a drink would stop its hydration ability.

A good sports drink should remaining effective as a hypotonic solution, but still provide steady electrolytes, carbohydrates and possibly even vitamins. The extra sodium, according to British researchers of Loughborough University, results in improved performance (Merson et al, 2008). Thus, marathon runners should apply this knowledge for best results.


Cohen, I. & Zimmerman, A.L. (1978). Changes in serum electrolyte levels during marathon running. South Africa Medical Journal, 25:53(12):449-53.

Merson, S.J., Maughan, R.J. & Shirreffs, S.M. (July, 2008). Rehydration with drinks differing in sodium concentration and recovery from moderate exercise-induced hypohydration in man. European Journal of Applied Physiology, 103(5):585-94.

Tortora, G.J. & Derrikson, B. (2006). Principles of Anatomy and Physiology. New York: John Wiley & Sons.

Published by David Despain, MS, CFS

David is a science and health writer living on Long Island, New York. He's written for a variety of publications including Scientific American, Outside Online, the American Society for Nutrition's (ASN) Nutrition Notes Daily, and Institute of Food Technologists' (IFT) Food Technology magazine and Live! blog. He's also covered new findings reported at scientific meetings including Experimental Biology, AAAS, AOCS, CASW, Sigma Xi, IFT, and others on his personal blog "Evolving Health." David is also an active member of organizations including the National Association of Science Writers (NASW), the American Association for the Advancement of Science (AAAS), the American Society for Nutrition, the Institute of Food Technologists, and the National Audubon Society. David has a master's degree in human nutrition from the University of Bridgeport, and a bachelor's degree in English from University of Illinois at Springfield. He also earned his Certified Food Scientist credential from the Institute of Food Technologists.

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