Hydration Physiology

Even mild levels of dehydration can initiate a cascade of physiological changes that impose cardio-respiratory stress, compromise thermoregulation, and significantly impair physical – and cognitive – performance. Follow the links below to learn more about the methods athletes currently use to make their best guess about their hydration needs, and the consequences of under-estimating them.

Everyone knows maintaining proper balance is important for general health and safety. But did you know that maintaining optimal hydration is vital for maximizing physical and cognitive performance? Do you know all the ways one can become dehydrated? Did you know one can become dehydrated in as little as 30 minutes of vigorous exercise?

Test your hydration knowledge below

Q: (T/F) Mild dehydration (2%-4% of body weight) often has no perceptible symptoms.
A: TRUE. One often doesn't have symptoms until they're already dehydrated.
Q: (T/F) Thirst is an adequate method of managing hydration.
A: FALSE. Thirst is a notoriously poor indicator of fluid needs. In fact, studies show that runners fail to manage their hydration appropriately up to 80% of the time, even when fluids are readily available.
Q: How much fluid does the average male runner lose during an hour run?
A: The average male can lose up to 55 ounces (1.6 liters) of fluid over an hour long run. A heavy sweater can lose up to 70 ounces (2 liters.)
Q: (T/F) Electrolyte drinks are more effective for rehydration than water.
A: This is a tricky one. Athletes should replenish what they're losing through sweat. Everyone sweats differently and therefore needs to replenish differently. The longer the activity, the more important electrolyte replacement will be. "Salty sweaters" are typically in need of electrolytes sooner than others.
Q: (T/F) Fluid needs are relatively consistent from one day to the next, even for the same activity.
A: FALSE. Most people know fluid needs can vary greatly from one person to the next. But fluid needs can also vary for the same person from one day to the next, even when performing the same activity. This varies with the weather, choice of clothing or equipment, workout intensity, activity duration and more.
Q: (T/F) Improper hydration management can have dire consequences.
A: TRUE. This seems obvious, right? What is not as obvious is that hyopnatremia (a low sodium concentration in the blood often caused by over hydration) can be even more catastrophic than dehydration. Maintaining a proper balance is critical to health and safety as well as maximizing performance.
Q: What is the physical performance impairment for someone just 3% dehydrated?
A: Studies show that mild dehydration causes cardio-respiratory stress resulting in a performance impairment of up to 29%. This could be the difference in breaking 3:30 in a marathon or running 4:00.
Q: (T/F) Currently, there is no simple, reliable way to measure one's hydration status.
A: TRUE. But not for long. Nix is developing a biosensor to inform athletes of their hydration status in real-time.