system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does swimming burn so many calories (close to higher intensity workouts) even if my heart stays in the warm up zone the whole time?
gpt
Swimming is a decent full-body workout, but it also means you’re immersed in water that’s significantly below your body temperature. Water is far more thermally conductive than air, and it has a very high specific heat, so it rapidly cools you down. Your body then has to raise its metabolic rate to keep you warm, and that burns calories.