To be considered for inclusion in the Summer Olympics, a sport must be widely played in at least 75 countries on at least four continents. The list of featured sports often changes, with IOC members regularly voting on whether to include or exclude particular sports. The only sports to have been included in every Summer Olympics are athletics, cycling, fencing, gymnastics and swimming. Some sports, like lacrosse and polo, were included just a few times early last century, and others like croquet and cricket were included just once. Baseball and softball were included fairly recently but then excluded again, while golf and rugby are being included again in 2016 for the first time in many years. Several other sports, like karate and squash, have never been included despite strong lobbying over many years.
Most Olympic sports are well-known and well-understood, but some of the less well-known are the "combined events" that include several activities in one sport, such as the men's decathlon and the women's heptathlon. In the decathlon, men compete in ten different track and field events, while in the heptathlon women compete in seven events. Both sports include running, throwing and jumping events, and both are held over two days. Competitors earn points in each event, and medals are won by those earning the highest total number of points. Another "combined event" is the modern pentathlon which originated as a test of skills needed by 19th-century European soldiers, and includes fencing, shooting, swimming, running, and show jumping. Another is the triathlon, which combines a 1.5km swim, a 40km bicycle ride and a 10km run into one continuous race. Unlike other combined events in which points are scored, the triathlon is a race to the finish, with competitors completing each stage as quickly as they can.
Equestrian sports are also among the less well-known Olympic sports. They are the only onesin which animals are used, with competitors riding horses in one of three events; dressage, show jumping and eventing. Dressage is a test of training in which horses and riders are judged as they perform a series of set movements, while show jumping involves horses and riders jumping a series of fences and water hazards on a winding course. Eventing is a combined event that includes dressage, show jumping and cross-country riding. All the equestrian sports feature both individual and team events, and they are among the few sporting events in which men and women can compete as equals.