Our results show that the gender gap in Olympic sport performance has been stable since 1983. These suggest that women's performances at the high level will never match those of men. This stabilization is the expression of a significant narrowing of gaps for all events (Cheuvront et al., 2005 ). Indeed, even when performances still improve, these progressions are proportional for each gender. The reduction and stabilization of the gender gaps in performance is a general pattern observed in all athletes and all disciplines (Figure 4). Stability appears through all of the parameters studied: coefficients of variation, slope coefficients, coincident breakpoint dates between world records and ten best performances. This stability is not affected by external, non physiological factors such as technology and doping advancements that could challenge it.



The yearly analysis of the number of world records shows a major, 22-year time lag in athletics between the men's and women's peaks, corresponding to the period where the fastest reduction in the gender gap occurred. After 1950, women began to benefit from improvements in training techniques that were developed from the men's training experience during the first half of the XXth century. Like men, they also benefited from a better medical and nutritional environment. The fast improvement rate of female performances' observed since then could also be explained by the increasing number of events proposed to women and by the investment of East European nations in women's sports (Geipel, 2001 ; Seppelt and Schück, 1999 ). In fact, the last period of acceleration in these improvements prior to the breakpoint date of the early 1980s coincides with published evidence of institutionalized doping. According to former GDR athletes, many of them were being administrated drugs to enhance muscle strength, aggressiveness and performance since 1966 (Franke and Beredonk, 1997 ; Geipel, 2001 ). However the trend linking performance-enhancing drugs and women in particular is still unknown. While it should be considered that the technological advancements leading to increased efficiency of some androgenic drugs on the physiology of female athletes could have played a role in some countries' investment in women's sport programs, the inverse could also be true. It may have been the idea of a potential progression margin in female sport as analyzed just after the Second World War, associated with the discovery of ergogenic and androgenic steroids that could have induced the interest and investment in the development of doping techniques to be applied to female athletes. Women doping during the 1970s could have sped up female progression and accelerated the gender gap reduction.



During the Cold War, many countries were fighting for the largest political influence. One manner in which to obtain international prestige was realized through athletic performance (Guillaume et al., 2009 ). While women's sports were not as developed as men's, east European countries, such as GDR, invested in female performance programs (Staatsplan 14.25) (Franke and Beredonk, 1997 ; Seppelt and Schück, 1999 ). With the use of androgenic steroids, beating records and winning medals were probably seen as an easier challenge for women than men. Such a strategy of optimized returns may have translated into an early and intense investment of communist countries in women's sport (Geipel, 2001 ; Seppelt and Schück, 1999 ), later followed by other countries or individuals (Guillaume et al., 2009 ). In fact, the geographical repartition analysis of world records evolution (Figure 5) shows a wider distribution of nations for women's athletics than for men's, with a women's domination by Russia after the Second World War, while men's competitions show a larger dominance by USA athletes.



Unlike athletics, a time lag is not observed in swimming, where women's competitions chronologically started much earlier. While men's first records were obtained in 1927 on average for all swimming races, women's world records were first set in 1932. Only 5 years separate the beginning of swimming competitions for each gender while 28 years separated the first men records (1914 on average for all events) from first women records (1942) in athletics.



In women's weightlifting, we did not detect a breaking point due to the recent introduction of women into this sport. Performances and gender gap have nevertheless both reached a plateau. Besides, 50.4% of world records in women weightlifting are set by Chinese athletes (Guillaume et al., 2009 ).



A recent and slight increase in gender gaps can be observed for 12 out of 38 events. This is not specific to any particular discipline, and corresponds to the enhancement of men's performances with a simultaneous regression or stabilization of women results. Also a small discrepancy is shown between the predicted year where women and men will reach world records asymptotic limits (2028 vs 2042 respectively) (Berthelot et al., 2008 ). Taking into consideration that men may continue to progress in a few events, gender gaps may slightly increase before reaching full stability (Seiler et al., 2007 ; Holden, 2004 ).



Random and unannounced drug testing was introduced in athletics in 1989. The declining use of banned performance-enhancing drugs may have also contributed to the most recent and slight increase of gender gaps. Men still improve, though at a lower rhythm, while women stopped their progression. Men are more likely to adopt behaviours at increased risk, whereas a higher percentage of women engage in preventive actions linked to health and longevity (Courtenay, 2000 ; Mercer et al., 2007 ). Another explanation could be the higher interest of media in male sport, and the greater rewards offered.



This major investment of East European countries in women's sport can be assessed by the annual cumulative proportions slope coefficient. Soviet Union has a slope twice as high as the USA's for women's world records during the 1970s and the 1980s. East Germany's progression slopes are always greater for women than for men and similar to the Russian women's progression for athletics. The percentage of women's world records obtained by GDR athletes is about 33.1% between 1970 and 1989 and 30.7% for the Soviet Union, compared to 11.2% for the United States of America and 3.2% for West Germany. This massive representation of two countries (Riordan, 1996 ; Seppelt and Schück, 1999 ), in which the incidence of doping was proven or highly suspected, could have accelerated the reduction of the gender gaps (Franke and Beredonk, 1997 ; Geipel, 2001 ). However, it should be clear that these are not the only nations in which female athletes have resorted to illegal performance enhancing procedures.



The connection between women's participation in international events and performance may not be quite relevant. On average, the mean date of the first men's world records was 1925 (± 21), while mean date for women first world record was 1955 (± 36). Despite a 30 year time lag average between men and women mean debuts, women rapidly progressed before the gender gaps stabilized. The number of participants in the Olympic Games is a measurable indicator of the involvement of elite athletes globally. Quotas and incentives of organizing authorities encourage the participation of women. While only 37 women attended the 1908 Olympic Games, in 2008 they represented 42.4% of all registered athletes (4746 women and 6450 men) at the Olympic Games in Beijing (International Olympic Committee, 2008 ). The number of competing women is still increasing while the number of men has reached a maximum at the 1988 Olympic Games in Seoul (Figure 4). After taking into account the evolution of world records previously studied in this analysis, there is no measurable effect of the increasing number of women participating in the Olympic Games on world records, ten best performances and gender gaps evolution. The major increase in women's participation takes place in the 1980s, while the world record peak already occurred (Berthelot et al., 2008 ), and the gender gaps stability period has begun.



A breakpoint date could not be detected in 3 events: pole vault (a female event not contested from 1930s to the 1960s), 5000m and 10000m due to their recent introduction into the Olympic program. Women's weight lifting world records only began in 1998, when most of men's world records had already reached their maximal values. This explains why gender gaps are still narrowing in this discipline (though at a slower pace in the last few years). The wide discrepancy between the magnitude of gender gaps in weightlifting and jumping events and the four other disciplines studied here could be explained by the different physiological mechanisms involved to mobilize energy. The predominantly explosive type of effort required in weightlifting and jumping (Maldonado-Martin, 2004 ; Wilmore and Costill, 2004 ) could explain the greater disadvantage that women have to face against men, compared to other disciplines.