system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why don't our hearts get stronger as we get older if its constantly exercising?
gpt
They also don't (hopefully) get to take a break and rest. Rest is an important part of building muscle. The heart works constantly. Sure it gets to slow down some while you're sleeping or lounging in a recliner, but even your resting heart rate is work.