Gabe Mirkin, M.D.
You will not become a better athlete by doing the same training regimen each day. Athletes train by taking hard workouts on one day, feeling sore on the next, and not taking another hard workout until the muscles stop feeling sore.
It's called the hard-easy principle. If you want to become stronger or faster or increase your endurance, you have to exercise hard or long enough to make your muscles burn. Then your muscles will be sore for one or more days. If you try to exercise hard when your muscles are damaged, you will tear them and the muscles will weaken. If you wait for the soreness to disappear, your muscles will be stronger than they were before your workout. As you continue to take stressful workouts only after the soreness disappears, you will become progressively stronger and faster and have greater endurance. Athletes in most sports train once or twice a day in their sports, but they do not exercise intensely more often than every 48 hours.
There is a difference between the good burning of training and the bad pain of an injury. The good burning usually affects both sides of your body equally and disappears almost immediately after you stop exercising. The bad pain of an injury usually is worse on one side of your body, becomes more severe if you try to continue exercising and does not go away after you stop exercising.