the.com/second wind

means A fresh surge of energy that kicks in after an initial period of tiredness during sustained effort, letting you keep going.

from The phrase comes straight out of athletics and exertion talk — the 'wind' here is your breath or stamina, the same 'wind' in 'winded' or 'catch your wind.' Runners and other athletes in the 1800s noticed a pattern: you start strong, hit a wall where your breathing feels ragged and everything screams stop, and then — if you push through — your breathing steadies and strength returns, as if your lungs had been reissued. It was originally literal, about actual respiration during physical strain, before it drifted into the broader figurative sense we use for any late-arriving burst of energy or resolve, physical or otherwise.