What is “getting your second wind” and how does our brain/body do it?

Question

I work a lot of double shifts at my job. My normal shift is on days, then I go home for a few hours and come back at midnight to work 16 hours. The first 5 or 6 hours are a slog, and I’m constantly trying to stay awake, but then I just reach a point where I feel “normal” so to speak, even energetic at some times. What causes this feeling? How do our bodies do this?

In: 28

Answer 1

Lot of psychology/sleep/biorhythm stuff here. Not discounting any of that, but in athletics, a ‘second wind’ is essentially when your body changes fuel sources. In general, your muscles store a small amount of glucose, and this is what they use to do work. Consuming this glucose produces water, CO2, and small amounts of lactic acid (the stuff that makes your muscles sore after a workout). When the glucose is exhausted, generally your body will start to move other sugars into your muscle cells to replace it. Roughly the same chemical reaction occurs. Finally, when those readily available sugars in your bloodstream are exhausted, your body will turn to stored energy, typically lipids (fat). Lipids are very high in energy concentration, but are not as easily broken down and produce more lactic acid. So if you are going for a run, and you can easily do a mile or two, but then get tired and push through, and then get your ‘second wind’ on mile 3 or 4, this is because you are now burning a more concentrated and powerful fuel. And also why you will be more sore the next day.

I’ve left A LOT out here, but this is ELI5. In relation to OP’s question, sleep cycle and what is now your ‘new’ circadian rhythm probably have a lot to do with it, especially if you are inside and don’t really see the sun. However, your body still uses the same ‘fuel.’ If you wake up and go to work for 5-6 hours, you probably have some stored glucose that you burn through fast and don’t really replace. When you go home and rest, you both replace that glucose and essentially ‘power up’ for the next 16 hour round. Because you have already burned off the ‘days’ worth of fast sugars, you are operating on the higher octane fuel for the second half of your shift. Thus, you feel more energetic and smooth for the second part.