TL;DR – In your next Olympic distance triathlon, try drinking at least every 5 miles on the bike, taking your last drink at mile 20.


With a drop in body water as little as 2%, endurance athletes may begin to experience the detrimental effects of dehydration, such as increased heart rate, increased body temperature and a better chance for muscle cramps.  This high cost of dehydration on performance shows why adequate hydration is an essential part of any endurance athlete’s race plan.  But, how much fluid intake is enough?  What, if anything should be added to just plain water? And when should most of your hydration occur?  You may be training and racing well below the optimal intake hurting your performance and not even know it.

Assuming you are starting your race or event already hydrated, the real answer is: your fluid intake should be equal to your sweat loss. The problem is sweat loss can vary from athlete to athlete and outside a laboratory environment it is almost impossible to determine. Drinking when thirsty is the simple answer, but thirst is a sign of already being dehydrated and many studies report athletes do a poor job of hydrating during events when no hydration plan is in place.  Given these challenges, fluid needs are best determined through estimated values and individual trial and error.

Studies have shown the human body can absorb up to 33oz (1000ML) of fluid per hour(1).  For hot and humid environments, or when exercising near max intensity getting as close to this amount as possible will help ensure adequate hydration since sweat rates are likely to be highest.  Since a standard cycling bottle is 28fl oz, the easiest solution is to consume one bottle per hour, or as close to this as your personal comfort will allow.

So, what should you add to your water for endurance exercise? Most of the research has focused on carbohydrate, protein/amino acids and electrolytes. Out of these ingredients only electrolytes and carbohydrate have been shown to increase performance during endurance exercise.  The largest increase comes from carbohydrate showing up to an 8% time advantage over water alone with few gastrointestinal issues for solutions containing 14-20 grams of carbohydrate per 8oz of water or 6-8%(2).  Research on protein and amino acids have shown mixed results with the only clear benefit coming from the sparing of muscle protein and a quicker recovery post-exercise. This faster recovery has led to an increase in performance in multiple day and longer events but not during single day and shorter events(3,4). Similar to protein, most of the research shows a performance benefit for electrolytes only during longer full distance/marathon type of events.  Last, if not using a flavored sports drink, adding your favorite flavor to your water bottle can be beneficial as there is a large amount of research that shows adding flavor influences an increase in fluid consumption.

Finally, when is the best time to consume your fluids?  For cycling events you are always in a position where drinking is easy, but for triathlon, running and swimming events it isn’t as simple.  Opportunities for fluid intake during the swim are non-existent and are severely limited during the run.  Therefore, the greatest chance to properly hydrate is during the bike portion of a triathlon.  A 2006 study of hydration during an Olympic distance triathlon found that hydrating early on the bike leg and drinking consistently every 5 miles ensured athletes were better hydrated and had faster finishing times(2).  In addition, taking your last drink at the 20 mile mark (Olympic distance triathlon), or 5 miles left to go during longer races, will ensure gastric emptying and improve athlete comfort on the run.

Variations in weight, gender, and carbohydrate tolerance can vary greatly which is why athletes need to use trial and error to come up with a personal race hydration plan to maximize performance.  Using trial and error athletes should try to consume up to a bottle an hour for hot environments or near max efforts, use a 6-8% carbohydrate solution, small amounts of protein or amino acids and electrolytes for full distance/marathon distance or multiple day events and should be consumed in small amounts before the swim and during the run, with the majority of fluids consumed on the bike leg. Now come up with your personalized hydration plan and go get’em!


Quick summary for your hydration plan:

  • Consume 1 standard cycling bottle an hour.

  • Drink at least every 5 miles on the bike with the last drink at the 5 miles to go mark.

  • Use a hydration solution that has 6-8% carbohydrate (14-20g per 8oz).

  • Adding your favorite flavor will influence drinking.

  • Protein and electrolytes added only for multiple day or full iron distance events.

  • Image Attribution: In-Boulder

    1. Rogers, J., Summers, R. W., & Lambert, G. (2005). Gastric emptying and intestinal absorption of a low-carbohydrate sport drink during exercise. International Journal of Sport Nutrition & Exercise Metabolism, 15(3), 220.
    2. McGawley, K., Shannon, O., & Betts, J. (2012). Ingesting a high-dose carbohydrate solution during the cycle section of a simulated Olympic-distance triathlon improves subsequent run performance. Applied Physiology, Nutrition & Metabolism, 37(4), 664-671. doi:10.1139/h2012-040.
    3. Hall, A. H., Leveritt, M. D., Ahuja, K. K., & Shing, C. M. (2013). Coingestion of carbohydrate and protein during training reduces training stress and enhances subsequent exercise performance. Applied Physiology, Nutrition & Metabolism, 38(6), 597-604.
    4.  Van Essen, M., & Gibala, M. J. (2006). Failure of protein to improve time trial performance when added to a sports drink. Medicine & Science in Sports & Exercise, 38(8), 1476-1483.