Final answer:
The statement is true; submersion in cold water can lower heart rate due to the activation of the mammalian diving reflex, a physiological response that conserves oxygen.
Step-by-step explanation:
The designed experiment aimed to determine the effect of cold water submersion on heart rate, which is rooted in a known physiological response called the mammalian diving reflex. This reflex, predominantly observed in aquatic mammals, is also present in humans and gets triggered when the face comes into contact with cold water, leading to a lower heart rate (bradycardia). In the described setup, the youngest volunteers' heart rates decreased while submerging their faces in cold water, compared to the oldest volunteers whose faces were not submerged. This aligns with the expected outcome due to the mammalian diving reflex, which conserves oxygen for vital organs by reducing the heart rate and subsequently the body's overall oxygen consumption. Hence, the data supports the hypothesis that submersion in cold water does indeed cause a lower heart rate, confirming that the statement is true.
The youngest volunteers had their heart rate measured while holding their breath with their face submerged in cold water, while the oldest volunteers had their heart rate measured while not submerged in cold water. The mean heart rate for the volunteers with their face submerged in cold water was found to be lower than the mean heart rate for those without.