Sodium Balance Study Research Results: Badwater Ultramarathon 2006

Researchers: Jeff Lynn, PhD, Lisa S. Bliss, MD, Joe Chorley, MD

At the Badwater Ultramarathon in 2006, we conducted a descriptive study investigating sodium balance. We recruited four race participants, 2 men and 2 women, and measured body weight, serum sodium concentration, urine sodium concentration, sweat sodium concentration, and urine specific gravity at 4 collection points: 1) before the race, 2) at Furnace Creek, 3) at Stove Pipe Wells, and 4) at the finish line. The subjects crews collected and recorded additional information to the best of their ability, including sodium intake from food, supplements, and electrolyte drinks, as well as amount of urine output.

Sweat patches were applied at each collection point and removed 20 minutes later and stored for later analysis at a hospital lab. Serum sodium was analyzed immediately with iSTAT point of care analyzers (Abbott Labs). Urine was collected in urinals and analyzed by the researchers at each collection point for specific gravity (which assesses hydration status) and urine sodium concentration. Weight was taken with calibrated scales.

All four runners completed the race and none required medical attention at any point. Although we were unable to gather complete data for all runners due to the challenges implicit in a field study of this type, we observed some trends in the data that we were able to collect. The trends were as follows:

• Those who reported the most heat acclimatization training prior to the race had a lower sweat sodium concentration at the start
• Sweat sodium concentration decreased in each subject as the race progressed.
• Urine sodium concentration increased in each subject as the race progressed.
• Serum sodium concentration remained normal in all subjects throughout the race.
• Weight changes during the race fluctuated between 0 and 2% for each subject.

Other observations:

• Sodium intake between subjects varied tremendously.
• Sodium balance homeostasis was maintained despite extraordinarily challenging conditions and bodily stress.

Future Plans:

• We will be submitting these data for publication.
• We will be conducting additional studies to investigate the physiological mechanisms responsible for these trends.