Experiment: The Diving Response: How Your Heart Reacts to Water

Human
Grade 6+

The Diving Response: How Your Heart Reacts to Water

How does your body react to being underwater? In this experiment, we explore how the nervous system responds when you submerge your face in water, triggering a unique physiological reaction!

What Will You Learn?

How the autonomic nervous system (sympathetic and parasympathetic) regulates heart rate.
How to record and analyze EKG signals using a Human SpikerBox.
How underwater submersion can induce different physiological responses.

Background

Our bodies are constantly responding to the environment, making adjustments to keep us balanced, safe, and functioning efficiently. Some of these responses happen so quickly and automatically that we don’t even realize they’re controlled by our nervous system. Think about times when you’ve felt startled—your heart might race, your breathing quickens, and you feel an instant surge of energy. Other times, like after a big meal, you might feel relaxed, sluggish, and ready to rest. These changes are driven by two key divisions of the autonomic nervous system: one that prepares you for action and another that helps you recover and conserve energy.

In this experiment, we’ll test how your body reacts to being submerged in water. By measuring heart rate changes, we’ll investigate how the nervous system adapts to different conditions and explore what this tells us about the way our bodies maintain balance in challenging environments.

Across the Animal Kingdom: A Shared Response to Water

The way your body reacts in this experiment isn’t unique to humans—it’s a trait shared by many mammals! Whether it’s a human, a dolphin, or a seal, the nervous system triggers similar responses when submerged in water. As you observe your own body’s reaction, you’re witnessing a survival mechanism that has evolved across species to help conserve oxygen and adapt to underwater conditions.

Experiment: Diving Reflex (Face Submersion)

Materials:
• A container large enough for your face
• Cool or moderately cold water (NOT ice water)
• Human SpikerBox and electrode patches

Setup:
1. If necessary. Replace the ice water from previous experiments with cool (but not freezing cold) water.
2. Keep the same EKG electrode placement (upper forearms + ground on the hand).
3. Record a baseline resting heart rate, then hold your breath.

Submerge your face. Gently dip your face into the water. A partner should monitor your heart rate. Remain submerged as long as is comfortable, still holding your breath.
Record the heart rate. Observe the changes as soon as the face contacts cold water, and note if/when heart rate decreases. Then remove your face and breathe normally—does the heart rate rise again?
Repeat. Rest a bit and repeat 2–3 times to get consistent data.

You’re observing the diving reflex.

Results & Analysis

Compare your average heart rate before, during the water submersion test. Did the diving reflex trial change the heart rate? Why is this so important for animals when they are underwater? Discuss how these findings align with either sympathetic vs. parasympathetic control.

Alternatives to Dunking Face in Water

Perhaps not everyone wants to submerge their face in water, but we can still activate the same physiological response using other methods. One effective alternative is placing a cold, wet towel on the forehead, cheeks, and under the eyes. This still targets the trigeminal nerve, which plays a key role in signaling the body to adjust its heart rate and circulation in response to cold exposure.

By using cold towels instead of full immersion, we can still observe the body’s natural reaction to water, making it a practical and accessible way to study this reflex in different settings!

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