" The runner who may just have completed a fast 400 meter repetition at a sub-5-minute mile pace, may drop to an 8 minute mile pace for a recovery lap. The jog might be carried out in much poorer, looser form whose purpose is to "shake out" the body and maintain circulation to eliminate the waste products of exercise metabolism . Competitive running Perhaps the most basic of athletic contests, running races are simply contests to determine which of the competitors is able to run a certain distance fastest. Today, competitive running events make up the core of the sport of athletics. Running competitions have probably existed for most of humanity's history, and were a key part of the ancient Greek Olympics, as well as the modern Olympic games. Events are usually grouped into several classes, each requiring substantially different athletic strengths and involving different tactics, training methods, and types of competitors. Running affects not only the body, but the mind as well. Barcelona Running Of The Bulls Runners who finish a great run are often said to have a "runner's high" - a strong feeling of accomplishment and pride. Some sources point to the origin of a runner's high being increased endorphin production as a result of exercise. "

" Road racing offers competitors a variety of challenges to overcome such as hills, sharp bends, varied pavement, inclement weather, and a large group to compete against- or with. Aerobic fitness, or the ability of the body to utilize oxygen, is important to have to complete the long distances. Anaerobic fitness, that is, the body's capability at responding when there isn't enough oxygen for the muscle, is necessary to charge up hills and past competitors on the finish line. A common saying for runners is that the sport is 90% mental. Recreational running became popular due to high-profile runners such as Steve Prefontaine. Race courses are usually held on the streets of major cities and towns but they could be on any sealed road. Most road races are either 5 km (3. Running Of The Bulls Fact1 miles), 10 km (6. 2 miles), half-marathon (21. "