Salting away data under the Texas sun

Fort Worth, TX

3/5/2008

Joel Mitchell is tracking down the science behind hydration for the Gatorade Sports Science Institute.

While summer 2007 didn’t break any heat records in Fort Worth, it was scorching in TCU’s Department of Kinesiology.

Fueled by a $19,000 grant from the Gatorade Sports Science Institute, department Chair Joel Mitchell, Assistant Professor Melody Phillips, graduate student Kimberly Hubing and a handful of assistants researched how sodium levels in endurance athletes such as marathoners and triathletes are affected by extensive exercise in sweltering weather.

“In other words, what causes low sodium levels in the blood?” Mitchell said. Another part of the research analyzed the connection between glycogen (stored sugar in the muscles) and fluid intake.

Nearly 85 percent of sodium in the body is found in the blood and lymph fluids. For the body to function, the intestines and kidneys must adjust sodium concentrations, with the intestines absorbing sodium while the kidneys excrete an almost equal amount in urine.

Because sodium is a key element in electrical impulse activity, abnormal levels impair neuromuscular function. The low-sodium condition — hyponatremia — is diagnosed through a blood sample. Normal sodium levels are 136-145 milliequivalents per liter (mEq/L) of blood. A blood sodium level lower than 135 mEq/L indicates hyponatremia.

Three people per 1,000 show symptoms, and some individuals are predisposed to the condition. A common cause is excessive water intake. A dehydrated person normally has high sodium; when she rehydrates, her sodium levels return to normal. Rehydrating too quickly can drive sodium levels too low because the excessive water dilutes the salt in the blood.

Most athletes know that dehydration is dangerous, but overhydration can also pose threats — nausea, loss of mental activity and, in extreme cases, seizures, coma or death.

“Because the symptoms of hyponatremia are similar to dehydration, an athlete might think he or she is dehydrated and drink too much fluid too quickly,” said Hubing, who is using the study for her master’s thesis.

Athletes are not the only group at risk. Since 2005, at least two high-profile deaths have occurred from forced water intoxication.

Matthew Carrington, a Chi Tau pledge at California State University, Chico, was allegedly forced to drink gallons of water during a five-hour hazing before he lapsed into a coma and died. Jennifer Strange, a mother of three, died after competing in a California radio station’s “Hold Your Wee for a Wii” contest in January. Contestants were asked to drink eight-ounce and larger bottles of water every 15 minutes without urinating to win a Wii game system.

The kinesiology department’s study traces its roots back a year, when Mitchell, student researchers and JPS Health Network fellows worked a medical tent at Wichita Falls’ annual Hotter’n Hell Hundred, one of the nation’s oldest and largest cycling events, with 9,000 athletes attacking a 100-mile course.

“Our role was to analyze the sodium levels of riders who appeared to be suffering from hydration problems,” Mitchell said. “We drew their blood and used a portable sodium analyzer to ascertain their sodium level.” Because of the scorching temperatures, the analyzer had to be stored in an ice-packed cooler.

This examination of riders served as a basic field study showing how heat affects an athlete’s physiology.

“This was a good real-world application, though it failed to provide strong science,” Mitchell said. “A pre-test and post-test analysis of athletes is really necessary to accurately gather factual scientific information, and the nature of the Hotter’n Hell prohibited us from doing this.”

For the Gatorade grant application, Mitchell designed a classic 2x2 controlled lab study that would enable his team to gauge 1) the process that causes sodium levels to drop, 2) the connection between glycogen, the storage form of sugar in the muscles, and carbohydrate intake, and 3) fluid intake in four controlled conditions.

(Because Gatorade contains sodium, it was not used in the study. “The good thing about the company is they are also interested in supporting research that helps us understand fluids in general, not just their own product,” Mitchell said. Gatorade has contributed smaller grants for TCU graduate research.)

The lab study began in June and concluded in November. Over four trials, 10 male endurance athletes did 90 minutes of intense stationary cycling in the kinesiology lab’s 100-degree environmental chamber. A three-hour rehydration recovery followed. Two days prior to each trial, diets were altered to manipulate glycogen levels, and during the 90-minute rides fluid consumption was regulated to produce the following four conditions:

* low-carbohydrate diet, dehydrated
* low-carbohydrate diet, hydrated
* high-carbohydrate diet, dehydrated
* high-carbohydrate diet, hydrated

The low-carb diet was used to drive the glycogen levels down. Participants consumed 30-50 grams of carbohydrates over the two days prior to their ride, which is less than 10 percent of a person’s normal carb intake. The high-carb diet was 600-700 grams prior to the ride, thus storing more sugar in the muscles.

Participants in the hydrated trial were given fluids at 100 percent of their sweat rate during the 90 minutes of exercise, followed by fluids at 50 percent of their sweat rate during the three-hour recovery. Dehydrated-trial participants received no water throughout the 90 minutes of exercise and 150 percent of their sweat rate during the recovery period.

Sweat rates were determined by weighing the athlete prior to and immediately after the 90-minute exercise. As long as fluids were not ingested and urine was not passed during the exercise, the weight loss was primarily the sweat rate.

The athletes were thoroughly monitored, Mitchell stressed. “Blood was drawn and sodium levels were analyzed every 30 minutes, and internal body temperature was monitored constantly. If a subject’s sodium level dropped below 135, fluid intake stopped [there was a comma after stopped; with or without changes the meaning] or if core temperature increased to 39.5 degrees Celsius during the cycling segment (normal core temperature is 37 degrees Celsius), we curtailed exercise. The athlete could continue the trial only after his temperature and/or sodium level returned to a more normal state.”

Mitchell said the athletes likely could have tolerated a bigger drop in sodium based on their pre-test results. “However, health and safety are of the utmost importance. We posed no risk to the subjects.”

Information gathered included blood samples, sweat rates, respiration exchange and sodium concentrations. Anti-diuretic hormone measurements showed how the body responds to the re-absorption of fluids.

Final trials were completed at the end of the 2007 fall semester, and a report went to Gatorade in January. The findings also will be presented at the American College of Sports Medicine national conference and the Texas regional chapter meeting. Hubing, who recruited the subjects, organized the trials and compiled the results, will present at both conferences.

“I feel that it’s important to give students an opportunity to be true researchers,” Mitchell said. “As a result, they gain a real appreciation for the nuts and bolts involved in setting up and conducting a real-world research trial.”

Mitchell said the research related to the relationship between glycogen and fluid seems inconclusive at first glance. “We didn’t make as much progress in that area as I hoped,” he said. “We may need a longer exercise duration in order to see the impact of glycogen levels on fluid and sodium status.”

He will continue this research with the prospect of more definitive findings.

“If what you learn in the lab can apply to someone in the real world,” he said, “you’ve made an impact.”

For more information on the student, contact Dr. Mitchell at j.mitchell@tcu.edu.