Abstract
What sport has been a core of the Olympics since 1912?
Modern pentathlon
Swimming at the Summer Olympics 5000 metres at the Olympics Modern pentathlon 400 metres hurdles at the Olympics 4×400 metres relay at the Olympics
Swimming_at_the_Summer_Olympics-Abstract 5000_metres_at_the_Olympics-Abstract Modern_pentathlon-Abstract 400_metres_hurdles_at_the_Olympics-Abstract 4×400_metres_relay_at_the_Olympics-Abstract
Swimming has been a sport at every modern Summer Olympics. It has been open to women since 1912. Along with track & field athletics and gymnastics it is one of the most popular spectator sports at the Games and the one with the second largest number of events (after Athletics). 
The 5000 metres at the Summer Olympics has been contested since the fifth edition of the multi-sport event. The men's 5000 m has been present on the Olympic athletics programme since 1912. The 3000 metres was the first women's Olympic long-distance track event, making its initial appearance at the 1984 Olympics, and this distance was extended to match the men's event from 1996 onwards. It is the most prestigious 5000 m race at elite level. 
The modern pentathlon is an Olympic sport that comprises five events: fencing, 200 m freestyle swimming, show jumping, and a final combined event of pistol shooting, and a 3200 m cross-country run. The sport has been a core sport of the Olympic Games since 1912, and since 1949 an annual World Championship has been held. Originally the competition took place over four or five days; however in 1996 a one-day format was adopted in an effort to be more audience-friendly. However, modern pentathlon, despite its long Olympic history, has had to justify its inclusion in the modern Olympic Games on frequent occasions. On February 11, 2013 in Lausanne, the IOC confirmed modern pentathlon once again as one of the 25 core sports of the Olympic program through until 2020. The governing body, UIPM, administers the international sport in more than 90 countries in all the continents of the world.
The 400 metres hurdles at the Summer Olympics is the longest hurdling event held at the multi-sport event. The men's 400 m hurdles has been present on the Olympic athletics programme since 1900, with a sole gap at the 1912 Summer Olympics. The women's event was added to the programme over eighty years later, at the 1984 Olympics. It is the most prestigious 400 m hurdles race at elite level. 
The 4×400 metres relay at the Summer Olympics is the longest track relay event held at the multi-sport event. The men's relay has been present on the Olympic athletics programme since 1912 and the women's event has been continuously held since the 1972 Olympics. It is the most prestigious 4×400 m relay race at elite level. At the 1908 Summer Olympics, a precursor to this event was held – the 1600 m medley relay. This event, with two legs of 200 m, one of 400 m, and a final leg of 800 m, was the first track relay in Olympic history. 