Once you've finished a race or tough workout, it doesn't mean your work is done.
To improve as an athlete, you have to do more than stress the body through exercise. You also need to focus on recovery to facilitate the body's adaptation process. Typically, a lot of thought, effort and pain goes into the stress process, but little goes into the recovery.
During exercise, the muscles burn glucose for energy and create lactic acid as a byproduct. Lactic acid is prevalent in the muscles after a hard workout or race.
If you stop being active as soon as you cross the finish line or sit on the couch after a strenuous bike ride, the lactic acid remains in the muscles, which has been shown to create delayed onset muscle soreness (DOMS). By performing a cool down—a slow jog or easy pedaling—you can help the blood in the muscles flush out the lactic acid, which limits DOMS.
Your muscles burn glucose for energy. The body has about 1,800 calories of glucose stored in the muscles and liver to use for energy during exercise. For workouts over an hour and half, or any excessively strenuous exercise or race, calories should be consumed to replace the glucose burned.
Right after a workout, your muscles need more glucose to replenish what was burned. The window to replenish is small—most believe consuming 100 to 300 calories within 30 minutes is crucial to replace burned energy so the muscles can start to heal and recover. There has been much debate over the proper carbs-to-protein ratio of recovery meals, but most dietitians recommend 3:1 or 4:1 (grams of carbs : grams of protein).