second breath
{n.}
1. The easier breathing that follows difficult breathing when one makes a severe physical effort, as in running or swimming.

After the first quarter mile, a mile runner usually gets his second wind and can breathe better.

We climbed with labored breathing for half an hour, but then got our second wind and went up more easily.

2. {informal} The refreshed feeling you get after first becoming tired while doing something and then becoming used to it.
Tom became very tired of working at his algebra, but after a while he got his second wind and began to enjoy it.

[TahlilGaran] English Idioms Dictionary ▲