Hi Liz, A drastic change in your fitness routine can be a blast, but also confusing to your metabolic gyroscope. I remember training heavily one summer and needing midday sleep like a third-shift zombie. I was the fittest sleepy person I knew.
Since Im no doctor, I cant claim to know why you, yourself, are sleepy. But nutrition can explain midday sleepiness for many people. It is widely suggested that eating small meals every four hours helps stabilize blood sugar levels so they do not dip too low. Making sure these meals are balanced with slow-burning carbohydrates, some fat, and protein will also help ensure fuel stays in the engine longer. And for those who are training twice a day, the sometimes-overrated sports nutrition establishment actually has something to offer.
Research now suggests there is a brief windowthe 45 minutes after you work outduring which your body is most ready to replenish the stored muscle fuel known as glycogen. The lack of this glycogen is one reason why someone could feel not so peppy out on the Frisbee field. Given a normal set of meals, your body would end up replenishing this fuel on its own during the next 24 hours, but a person training twice a day might want to hit that recovery window right after they work out.
As for the nutrient content of a recovery drink or meal, it used to be thought that just getting fast-burning carbohydrates was sufficient, but recent studies have shown that a small amount of protein mixed with carbohydrates helps you leverage even more sugar into your muscles during this window. They sell drinks that offer this comboand the whey protein they contain is metabolized faster than regular proteinbut you could also eat a peanut butter sandwich and get a similar effect. Another cause of lethargy can be over-training (often the result of training at intensity too frequently), which is why adequate recovery is often the main concern and management question for endurance coaches.