Marathon runners and bicycle racers will recognize the scene immediately: a large group of athletes standing close together, stretching their legs and mentally preparing for the race ahead. These athletes are in queue to start the race through a mass start, in which a large number of racers begin the race all at once. The mass start is often chaotic and slow, but as the racers spread out, the pace quickens and the group breaks up. Jockeying for position is common during a mass start, and crashes, bumps, stumbles, and other obstructions to forward progress are common.
In cycling, a mass start can be executed two ways: either the racers begin the race on their bikes all at once in a large pack, or they begin the race on foot in what is known as a le mans start. During the le mans start, the cyclists must run a set distance before mounting their bikes to begin riding. This helps break up the group quickly so the riders do not get bottlenecked on the race course. The le mans mass start is particularly difficult because it immediately begins to tire muscles the racers will need once they mount their bikes.
In running, a mass start is common at marathons and other long-distance races. The racers will have ample time to break away from the group during a longer, marathon race, whereas during a shorter race, it may be difficult or impossible to break from the group at all. Most shorter races are broken into categories, generally by ability level, to limit the amount of competitors running a race at once. In some cases, racers are broken into separate lanes so they do not crowd each other. During a mass start, the racer is free to run where he or she pleases, provided he or she stays within the course markers.
Mass starts can also take place in other sports such as auto racing. During many auto races, the competitors are assigned a starting position, but the group starts all at once. The competitors must jockey for position from there. While the racers are racing at a slower speed during the start than they will race later on, accidents are most common during the start because so many cars are in such close proximity, and because they are all trying to move forward in the pack. It is not uncommon to see multiple-car pile-ups during mass starts.