Dog Days of Summer - Fluid Replacement #2

The start of fall sports really isn’t during the fall here in Missouri. Official fall sports practice  begin when the daytime temperatures average around or above 90° with plenty of sunshine and high humidity beating down on the athletes. Hydration is vital to maintain the athlete functioning properly, both mind and body. It has been shown that even a small 2 percent reduction  in total body weight (example:  a 3lb loss in a 150lb athlete) through sweat causes decreases in both physical and mental performance.1,2 An athlete who becomes dehydrated is at a greater risk for heat stroke, heat exhaustion or heat cramps.

Coaches often encourage their student athletes to make sure they are hydrated but are now becoming more and more concerned about what type of fluids are being consumed. Two of the most popular beverages for athletes are water and sports drinks. But the question that is asked frequently is which is the best choice? Water or Sports Drinks?   

When an athlete participates in the vigorous physical activities of practice during a typical Missouri August day they will sweat, a lot.  Sweat is composed primarily of water, some of this coming from the blood which leaves behind more concentrated electrolytes (example:  salt) in the blood plasma.  Thirst is primarily is driven by a drop in blood volume and an increase sodium levels. Even with this fluid loss, many athletes do not drink enough to stay hydrated, many times they rely only on thirst as a cue to drink.    Water quenches thirst while only replacing some of the fluid, this happens because the sodium level in the blood fall.  The athlete in this case is still dehydrated but no longer thirsty.  A sports drink is many times the better choice as it helps to maintain thirst often times allowing the athlete to consume enough fluid as it helps to maintain the electrolyte balance, unlike water.

How do you determine if your athletes are returning hydrated to the next practice? A simple charting of their weight pre and post practice can be used. The weight lost from sweat, should be replaced by the next practice.  A rough guide is for every pound lost, 24oz of fluid need to be replaced. If there is still a reduction in weight encourage them to drink a bit more throughout the day. Another is to do a simple bit of education, ask your athletes to look at the color of their urine. Dark like apple juice means poor hydration while light like lemonade indicates good intake of fluid.

It is most important that athletes be allowed to go and get a drink when they are thirsty as well as during water breaks. Sometimes the body demands fluid replacement at a different time than at a set water break. Let your athlete’s body help them learn how to properly maintain hydration.  Also encourage them to remember to replace all fluids lost during practice before the next practice.   

I.    Gisolfi, C. V. and Lamb, D. R. Perspectives in Exercise Science and Sports Medicine: Fluid Homestasis During Exercise. I pp. 1-38, 1990

2.    Gopinathan, P.M. et al. Archieves of Environmental Health, 43: 15-17, 1998.

Hyponatremia? Huh?

What is all the talk about hyponatremia?  Find out at www.gssiweb.com.  Search the Gatorade Sports Science Institute for this and other information concerning proper hydration.

Joanna Z. McClarey, M.S., ATC, LAT