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Running on Empty: The Science of Dehydration

In Running on Empty: The Science of Dehydration, Jem pushes his body to the limit with intense exercise while scientists measure how dehydration affects his performance. After sweating it out on a treadmill and exercise bike — without drinking any water — his blood volume drops, and his reaction time slows by a third! The results prove just how crucial hydration is for both the body and the brain. This video is excerpted from BBC’s Bang Goes the Theory, a series that delves into the ways science impacts our lives and shapes the world we experience every day.

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Bang Goes the Theory
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5:51
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Lesson Express

Q: Why do you think Jem’s cognitive test scores dropped so significantly after dehydration? What does this reveal about the brain’s dependence on water?
A: The brain relies on proper hydration to function efficiently, as water helps deliver nutrients and remove waste. When dehydrated, the brain has less oxygen and energy to process information quickly, which explains why Jem’s reaction time slowed so much.

Q: How does this experiment challenge the common idea that thirst is the best indicator of when to drink water?
A: The experiment shows that by the time Jem experienced performance decline, he was already significantly dehydrated. This suggests that thirst isn’t always a reliable signal and that people should drink water regularly to prevent negative effects before they begin.

Q: In what real-life situations might the effects of dehydration seen in this experiment be dangerous?
A: Dehydration could be dangerous in activities requiring quick thinking and endurance, such as sports, driving, or operating machinery. It could also impact decision-making in high-pressure environments like emergency response or military operations.

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