On: When muscles work out, they help neurons to grow, ...

[myth_drannon]

How much of it is just reduced CO2 from being in the open air vs sitting in a stuffy office?

[tpm → myth_drannon]

Not much I would think - there is a clear difference between just being outside and being outside while expending lots of energy, at least for me.

[tsunamifury → myth_drannon]

More the deep breathing triggered by a hill climb or brisk walk than the actual atmosphere.