Quenching the Exercise-Induced Thirst

How we help our personal training clients hydrate during a workout is a topic worthy of a certain degree of physiological understanding The human body is a highly-evolved and finely-tuned machine, capable of performing a myriad of functions at any given moment in time. For all of its complexities and intricacies, the fact that water comprises 50-65% of the human body may come as a surprise to many.

The ability of water to disassemble and rearrange other molecules is essential to the chemistry of life, a magnificent biochemical feat accomplished through the formation of weak bonds with other molecules. This is often why water is referred to as “the universal solvent”. Water is a perfect conductor of electricity, thereby becoming vital to the day-to-day operation of our bodies.

Athletes are well-versed in the importance of adequate hydration. Even the very earliest stages of dehydration can begin to affect athletic performance. As the body loses water through sweating, its core temperature rises, which in turn can compromise metabolic pathways, interfere with cardiovascular functioning, and reduce total exercise capacity.

Symptoms of dehydration include muscle weakness, dizziness, headache, fatigue, cramps, and thirst. This last symptom should not be relied on as a sole indicator of trouble, since an athlete can enter a state of dehydration and not experience the sensation of thirst for several hours, at which point rehydration becomes much more challenging.

One of the more controversial topics among recreational as well as elite-level athletes is determining when something more than plain water might be required for optimal performance and rehydration. In the 1950’s, physiologists discovered that there are two quite separate mechanisms for absorbing water from the gut into the bloodstream: an active mechanism and a passive mechanism. The active pathway can shift 10 -100 times more water than the passive one. Glucose and sodium are required in sufficient amounts in order for this to be effective, and this pathway uses these chemicals to drag water out of the gut into the body’s circulation system.

By the 1960s, this knowledge had led to the first modern use of oral rehydration therapy, which was nothing more glamorous than carefully measured salts and sugars dissolved in water. This treatment, utilized initially in cases of life-threatening dehydration resulting from diarrhea, proved to be more cost-effective and easier to deliver than intravenous fluids. Indeed, it was this particular research which paved the way for the development of the sports drink.

The pioneer of all modern sports drinks is, of course, Gatorade. This beverage was invented in 1965 at the University of Florida, to support the losing Florida Gators football team. The games in this hot, humid climate often lasted for hours; the players sweated massively and did indeed suffer from mild dehydration. As it happens, the rehydrating effects of the sugars and salts in the Gatorade did help the Florida Gators achieve victories, while sparing the athletes too many further ill effects. Thus, we saw the dawning of a new market niche, the electrolyte replacement beverages.

How is an electrolyte-laden beverage helpful for an athlete? To answer this effectively, it is best to have a comprehensive understanding of the importance of electrolyte balance in the body. Electrolytes regulate the fluid balance between body compartments. They help to maintain an acid-alkaline balance, which is required for normal cellular activities, and carry electrical currents which facilitate the control of hormone and neurotransmitter secretion necessary for nerve and muscle function. Electrolytes are also needed as cofactors for the enzymes which influence a number of vital reactions in the body.

Some of the more critical electrolytes whose delicate balance can be thrown off- kilter during extreme exercise/sweating are magnesium, sodium and potassium. Magnesium is needed to deliver oxygen to working muscles during vigorous training. Magnesium depletion may reduce physical performance and reduce exercise capacity. Sodium maintains blood volume and helps preserve the balance of water within the cells. Potassium helps to facilitate increased endurance. Both sodium and potassium work to regulate muscle control, nerve function and blood pressure.

When Will “Just Water” Do?

While it is tempting to grab a brightly-colored bottle of electrolyte solution on your way to the gym, it is equally important to grasp when true replacement is actually necessary, and when a bottle of plain water will suffice. When engaging in a light workout that will last less than an hour in duration–yard work, brisk walking, swimming–water is the ideal aqueous solution for peak performance. The extra sugars, sodium and calories found in an average sports drink may simply promote weight gain, and the costs outweigh any minimal benefits that may be derived from their consumption.

Another more frightening consideration for recreational athletes is the potential of over-consuming certain electrolytes. While the body does lose sodium during exercise-induced sweating, especially when training outdoors or in intense heat and bright sunlight, too much sodium will maintain the sensation of insatiable thirst, leading to fluid overdose. Manufacturers of sports drinks defend the sodium content of their products, claiming that the purpose of more sodium is to encourage hydration. However, overhydrating during physical activity could cause cramping and have a negative impact on overall performance. Extremely high levels of sodium can cause swelling of the brain, which can lead to a rise of inter-cranial pressure and restriction of blood flow, resulting in the killing of brain cells, brain damage, or even death.

For an intense activity that will find an athlete exerting energy for more than 3 hours, sweating profusely or competing in a high-altitude environment, a sport beverage is definitely a prudent choice. Not only will it replace lost electrolytes, but it also provides a boost of needed carbohydrates. Athletes prepare for intense exercise by eating a diet rich in carbohydrates the day or two prior to a competitive event. During exercise, however, eating is not an option. Sports drinks quickly inject carbohydrates into the body, allowing for the maintenance of sufficient energy levels. According to the University of Georgia’s University Health Center, carbohydrates are the fuel of choice for the muscles and brain. When the body is carbohydrate-depleted, one will feel fatigued, both mentally and physically. Though the body produces carbohydrates on its own, it cannot produce enough to sustain even a seasoned athlete through intense and prolonged exercise.

A considerable amount of practice and training must go into the preparation for a competitive athletic event; similarly, it might take a bit of trial and error and experimentation in order to identify the perfect balance of fluid, carbohydrates, and electrolytes to suit one’s unique metabolic needs. A solid understanding of the dynamics between hydration and human performance will help in these decisions. Rest assured, there is a perfect “aqueous solution” for every active body!






Cathleen Kronemer is an NFPT CEC writer and a member of the NFPT Certification Council Board. Cathleen is an AFAA-Certified Group Exercise Instructor, NSCA-Certified Personal Trainer, ACE-Certified Health Coach, former competitive bodybuilder and freelance writer. She is employed at the Jewish Community Center in St. Louis, MO. Cathleen has been involved in the fitness industry for over three decades. Feel free to contact her at [email protected]. She welcomes your feedback and your comments!