In 1896 Charilaos Vasilakos won the first modern marathon, a qualifying race for Greece’s Olympic team, with a time of three hours and eighteen minutes. Today that would not even qualify him for the Boston Marathon. Since the beginning of the modern Olympic Games world records in every sport have advanced sharply, driven by factors as disparate as global conflicts, social change, technological improvements and changing rules.

The general upward trend in performance is largely due to advances in our understanding of fitness, conditioning, diet and nutrition, says Mark Williams, a professor of sport, health and exercise science at Brunel University in London.

But this progress has not been steady, and many things have helped or hindered it. As an example, Geoffroy Berthelot of the National Institute of Sport and Physical Education—INSEP in Paris highlights the stagnation of most records during World War I and World War II. “When you have world wars you don’t focus on sport competition,” Berthelot says. But conversely, the cold war led to the Soviet Union and its satellites developing a rigorous scientific approach to athlete improvement—an aggressive illegal doping program notwithstanding. Some event records set during that time have never been beaten, such as the Men’s Hammer Throw world record, which was last broken by Soviet hammer thrower Yuri Sedykh in 1986 at the European Championships in Stuttgart, three years before the fall of the Berlin Wall and five years before the U.S.S.R. collapsed. “Today we have a lot of difficulty [with breaking the records] because athletes use less doping substances,” Berthelot says.

Social change can also drive performance, as it seems to have done in women’s marathon times. Women were excluded from performing in many such events, including the Boston Marathon, because it was commonly believed their constitutions could not handle long races. In 1966 Roberta Gibb hid in the bushes beside the starting line of the Marathon and became the first known woman to complete the course. The next year Kathrine Switzer entered the race under the name K. V. Switzer, and photos of the race organizers trying (unsuccessfully) to remove her forcefully mid-race made international headlines. These events coincided with Second-Wave feminism in the U.S., and a dedicated campaign brought the Women’s Marathon to the 1984 Summer Olympics held in Los Angeles.

Technical breakthroughs have also played a role, as illustrated by the evolution of the high jump. At the 1968 Olympics in Mexico City, U.S. Olympian Dick Fosbury shocked the world with an innovative technique called the Fosbury flop, in which he turned his back to the bar when he jumped, rather than cross it face down. Fosbury won the gold medal that year but did not break the world record. It would take several years for athletes to do so using the technique, which would ultimately enable dramatically higher jumps. That kind of advancement is not uncommon, says Jordan Taylor, a psychologist at Princeton University who studies skill acquisition. “What happens is that you basically get a little bit of a slowdown until someone comes up with a new strategy—and then when you have a new strategy, it takes a little bit of time to refine it, and then you see the progression go on,” Taylor says.

The pace of world record–breaking has slowed, as humans reach physiological limits and the International Association of Athletics Federations cracks down on doping. Berthelot is an author on two papers that suggest the rate of world record–breaking peaked in 1988. There are some exceptions to the general slowdown that has followed. One is swimming, but Berthelot calls this progress a “technological artifact” that came from the brief adoption of polyurethane swimsuits in 2008–09—and his paper suggests that, in swimming at least, we should get used to the records we have.