Second wind

Second wind means that when you run very fast, you reach a point where you gasp for breath, slow down but keep on pushing and after a few seconds, you feel recovered and pick up the pace. Some people think that you just slow down and allow yourself enough time to recover from your oxygen debt, but research from the University of California in Berkeley may give another explanation.

When you run fast, your muscles use large amounts of oxygen to burn carbohydrate, fat and protein for energy. If you run so fast that your lungs cannot supply all the oxygen that you need, you develop an oxygen debt that causes lactic acid to accumulate in your muscles to make them burn, and you gasp for air. The muscle burning and shortness of breath caused by the accumulation of lactic acid forces you to slow down. This research shows that the lactic acid that accumulates in muscles when you run very fast actually is the first choice of fuel for your muscles when you are running so fast that you can't get all the oxygen that you need (American Journal of Physiology- Endocrinology and Metabolism, June 2006). So your muscles switch to burning more lactic acid for energy, you need less oxygen and then you pick up the pace. Of course when you keep on pushing the pace, you can again accumulate large amounts of lactic acid in muscles, which makes them burn and hurt again.