system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is actually happening with the body when you "catch your breath"?

How does this process differ between a person who is in shape and someone who is not?
gpt
Being out of breath is caused by high acid levels in the blood: carbonic acid from carbon dioxide (CO2) and lactic acid. Both are produced by strenuous exercise. You catch your breath by exhaling CO2 and inhaling oxygen which is needed to convert lactic acid to water and CO2.

This process doesn't differ much between people in or out of shape. A person who is in shape may have a higher lung capacity and their muscles may convert lactic acid faster if they're trained.