Hydration

Yesterday I spent the morning cheering on runners at the inaugural San Diego Beach and Bay Half Marathon.  It was a great time and I reached a personal record! That’s right, I reached a personal record in receiving the most sweaty hugs in one day.  I could have wrung some of those runners out and had buckets of sweat.  Sweating is good though, it helps thermal regulate the body. What is your body losing in that sweat and how should you replace it to help regulate body temperature and metabolic processes?  All those sweaty hugs inspired this blog!

Over the years, the recommendations for hydrating during endurance exercise have changed.  The first recommendation was to drink, “as much as tolerable”.  Dr. Timothy Noakes stated in 2003 that there were 250 documented cases of hyponatremia (low blood sodium) from 1985-2001, with the runners reporting that they had followed the standard recommendation of “drink as much as tolerable”.  One is at risk for hyponatremia not only when they sweat and don’t replace it with fluids, but when they sweat and they rehydrate with lots of water only, basically diluting the sodium in their blood.  Our bodies are actually made up of 60% water and rehydrating with water is fine if you are running for less than an hour, but when running for more than an hour your fluids should also be supplemented with a sports drink containing electrolytes.
Sweating isn’t just about losing fluid.  It isn’t water out, water in, to maintain balance.  Von Duvillard and colleagues (2008) refer to fluid balance as a complex process and exercise challenges the body to regulate fluid and electrolytes.  The electrolytes, sodium and potassium are important micronutrients for maintaining optimal performance in half and full marathon running.  Sodium and potassium replacement are important in endurance exercise not just for hydration maintenance, but for maintaining plasma volume.  Sodium maintains or increases plasma volume by improving water and glucose (sugar) absorption in the small intestine, therefore aiding performance variables.  Benardot (2012) refers to performance variables as the ability to maintain sweat rate, deliver nutrients to cells, and clear metabolic waste from cells.  Yikes! The body is a machine and just like your car, you have to keep it fueled (or charged these days), lubricated, filters in check, tires pumped up, and alignment correct.

Later, Noakes suggested that runners should drink ad libitum, which is as needed, dictated by thirst.  However, some will say that if you wait until you are thirsty, then dehydration has already set in.  Drink too little, end up in the medical tent dehydrated!  Drink too much water and end up in the medical tent with hyponatremia!  Drink too much Gatorade on the course, along with salt tablets, and sodium containing nutrition, end up in the medical tent with hypernatremia (high blood sodium)! 

So what is the recommended formula?  According to the American College of Sports Medicine (ACSM) the current recommendation to best maintain fluid balance and optimal performance variables is drinking 3-8 ounces of water every 15-20 minutes for exercise less than 60 minutes and 3-8 ounces of sports drink every 15-20 minutes for exercise over 60 minutes.  This is a pretty large spread and variables that should be considered are metabolic requirements, climate, altitude, duration, clothing, and individual sweat rates (Sawka et al., 2007). 

I personally have high hydration needs.  I ran eight miles at an aerobic pace and drank 20 ounces of fluids, which was close to 5 ounces for every 16 minutes. This was conservative for my needs, taking the length of the run into consideration.  Had I run longer, I would have needed to drink more fluids earlier on to better maintain my hydration status.  The key is to play around with your fluids during your long training runs.  Keep a log of how much you drank and how you felt during the run and equally important, how you felt the remainder of the day.

Okay, so the next blog will be about arthritis!

Fight ON!
Coach Gina

References
Benardot, D. (2012).  Advanced sports nutrition (2nd ed).  Champaign, IL: Human Kinetics.

Noakes, T.  (2003). Fluid replacement during marathon running.  Clinical Journal of SPORT
MEDICINE, 13(5), 309-318.

Sawaka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007).  Exercise and fluid replacement.  Medicine & Science in Sports & Exercise, 39(2), 377-390.

Von Duillard, S.P., Arciero, P. J., Tietjen-Smith, T., & Alford, K. (2008).  Sports drinks, exercise training, and competition.  Current Sports Medicine Reports, 7(4), 202-208.