To compete in sports that require speed, athletes use a technique called interval training. They exercise for a short period at a very fast pace, rest until they recover and then repeat these fast bursts until their muscles start to stiffen and hurt.
Interval training teaches your brain to coordinate muscles at a very fast pace. The principle behind interval training is to move so fast that lactic acid accumulates in muscles, causing burning and hurting.
Your muscles get their fuel from fat and sugar that are broken down by chemical reactions that release a little energy at a time. If there is enough oxygen in your bloodstream, the sugar and fat are broken down into carbon dioxide and water. If you exercise so vigorously that you can’t get enough oxygen, the sugar cannot be broken down and the reactions stop, causing a chemical called lactic acid to accumulate in your muscles. This makes your muscles hurt. When you rest, lactic acid levels drop and the discomfort disappears. You run hard again, causing lactic acid to accumulate, rest, and repeat these hard intervals until your muscles start to stiffen up.