From Ironman Switzerland, an official qualifier for Ironman Hawaii, the age of the annual top ten women and men was determined between 1995 and 2010. The data set from this study was obtained from the race website 20 . Ironman Switzerland is an important Ironman event in Europe because of the numerous qualifying places for the Ironman World Championship in Hawaii, the high participation rates, and its long history. It is the third oldest Ironman in Europe behind Ironman Europe (Germany) and Ironman Lanzarote (Spain). Since 1995, the event has been held in July each year in the city of Zurich. For the first 2 years, it was called Euroman and changed to Ironman Switzerland in 1997. Course records are 8 h 12 min for men (Oliver Bernhard in 2000) and 9 h 00 min for women (Karin Thürig in 2010). In 2010, more than 2,000 triathletes from more than 50 different countries started in Ironman Switzerland, and the female rate was 13.5%. Since 1995, almost 18,000 triathletes have competed in this race. Concerning qualifying places, Ironman Switzerland with 50 qualifying places for a start place at the Ironman World Championship in Ironman Hawaii is comparable with other qualifiers for Ironman Hawaii 21 . The course is held on a two-loop swim, a two-loop cycling course with 1,260 m of altitude gain, and a flat run course. The age at the time of competition and swimming, cycling, running, and overall race times of the top ten women and men in Ironman Switzerland were analyzed from 1995 to 2010. All times were converted to minutes. Age was calculated as the difference of the calendar year of the race minus the athlete's year of birth. The magnitude of gender difference was examined by calculating the percent difference for swimming, cycling, running, and overall race times of the top ten men versus the top ten women. The top ten time spread, i.e. the time difference between the winner and the tenth placer, was analyzed and expressed as a percentage of the winning performance for both women and men over the 1995–2010 period.

A cross-sectional analysis of the age of peak performance was performed for all Ironman triathlons held in 2010. In 2010, a total of 22 Ironman triathlons, including 21 qualifier races and the Ironman World Championship, the Ironman Hawaii, were held. Complete data from the Ironman World Series 2010 were available for Ironman Hawaii and for all qualifier races held in 2010, with the exception of Memorial Hermann Ironman Texas, Ironman Wales, and Ford Ironman Cozumel 21 . From these three races, the complete rankings were not publicly available online, and the race directors were not able to provide us the data needed for analyses. Therefore, from 19 qualifiers and Ironman Hawaii, the exact ages of the top ten women and men were available. Since no information about age of the athletes was given for 2 out of the 21 qualifier races, these two races were excluded from analysis. From the other 20 competitions, the age of the overall top ten women and men at the time of competition was determined and analyzed.

For the cross-sectional analysis, a Mann–Whitney test was used to compare the age of peak Ironman performance between women and men in each Ironman held in 2010. For the longitudinal analysis, linear regressions were used to estimate the changes in age and performances (split times, transition times, and overall race times) across the years 1995 to 2010. Pearson's correlation coefficients were used to assess the association between various variables. Effect size (Cohen's d) was defined as ‘small’ for 0 < d < 0.2, ‘medium’ for 0.2 < d < 0.5, and ‘large’ for 0.5 < d < 0.8. A one-way analysis of variance (ANOVA) was used to determine if the age of the top ten women and men differed over the studied period and to compare gender differences over the three disciplines. Tukey's post hoc analyses were used to test differences within the ANOVAs when appropriate. Statistical significance was accepted at p < 0.05 (Statsoft, Version 6.1, Statistica, Tulsa, OK, USA).

Table 1 presents the age of the top ten women and men for each Ironman race held in 2010. In 19 of the 20 analyzed Ironman qualifiers held in 2010, there was no age difference between women and men (p > 0.05). The only age difference between the genders was seen in Ironman Canada where men were older than women (p = 0.023). For all 20 races (19 qualifier and Ironman Hawaii as the World Championship), the age of peak Ironman performance was 32.2 ± 1.5 years for men and 33.0 ± 1.6 years for women, respectively (p > 0.05). When Ironman Hawaii was excluded, the age of peak Ironman performance was 32.0 ± 1.4 years for men and 33.0 ± 1.6 years for women, respectively (p > 0.05).

*Significantly different (p = 0.023).

From 1995 to 2010, there were 17,786 finishers in Ironman Switzerland (1,847 women and 15,939 men). The number of finishers each year over the history of the event is shown in Figure 1. There was a progressive rise in the number of finishers since 1995 for both sexes. Women accounted for 10%–14% of the field since 2001. From 1995 to 2010, there was no age difference between genders (F = 0.06, p = 0.8) for the top ten women and men (Figure 2). During this period, the mean age of the top ten women and men was 31.4 ± 1.7 years and 31.5 ± 1.7 years (Cohen's d = 0.06), respectively. The mean ages of male and female winners were 31.9 ± 3.5 years and 31.6 ± 3.7 years (Cohen's d = 0.08), respectively.

Figure 3 shows the historical performance trends of the top ten women and men between 1995 and 2010. Over this period, the mean swimming, cycling, running, and overall race times were 54.1 ± 3.1 min, 292.4 ± 8.9 min, 177.5 ± 4.4 min, and 527.3 ± 10.6 min for men, respectively, and 61.4 ± 4.3 min, 331.0 ± 16.0 min, 209.6 ± 8.7 min, and 605.9 ± 25.2 min for women, respectively. Regression lines are presented from 1995 to 2010 for the three disciplines and the overall race times for both genders. The gradient of the regression lines demonstrates that swimming and running performances have not significantly (p > 0.05) changed for both genders during the 1995–2010 period (Figure 3). In contrast, cycling times decreased significantly (p < 0.001) by approximately 3.1 min/year for women and by approximately 1.6 min/year for men, respectively. Men improved overall race times by approximately 1.2 min/year (p = 0.03) and women by approximately 4.2 min/year (p < 0.001), respectively. Regarding total transition time, ANOVA showed a main effect for gender. Total transition time in Ironman Switzerland was significantly longer for top ten women (4.37 ± 1.65 min) compared to top ten men (3.51 ± 0.98 min) during the studied period (p < 0.001).

Figure 4 shows changes in gender difference in swimming, cycling, running, and overall race times between 1995 and 2010. Over this period, the difference in times decreased significantly in the three disciplines and for overall race time. The mean gender differences were 14.0 ± 5.4% for swimming, 13.2 ± 2.4% for cycling, 18.2 ± 4.1% for running, and 14.9 ± 2.9% for overall race time, respectively. The gender difference in running performances was significantly greater compared with swimming (p = 0.016) and cycling (p < 0.01).

The relative time difference between the winner and the tenth placer for both women and men is shown in Figure 5. During the studied period, the tenth–first difference remained stable for men and decreased slightly for women. The mean tenth–first difference was 7.5 ± 1.3% for men and 10.4 ± 3.3% for women, respectively.

Previous studies regarding the age of peak endurance performance showed that the age of peak performance was relatively constant over centuries because of the large role played by biological factors 1 2 . Data about the age of peak endurance performance can be useful in order to gain more detailed information about the physical development of humans 1 and to plan an athletic career. However, the potential gender difference in the age of peak endurance performance has been sparsely investigated and controversially discussed 1 4 5 6 . The present data showed that both male and female Ironman triathletes reached peak Ironman performance at the same age of around 32–33 years. Even if the Ironman triathlon is young in the field of ultra-endurance events with the first Ironman taking place in Hawaii in 1978 18 , and Ironman triathletes started with triathlon later in their life coming from a variety of sporting backgrounds with most from running, followed by swimming and cycling 22 , the finding of no gender difference in the age of peak performance was constant over the 16-year period analyzed in Ironman Switzerland and confirmed by the cross-sectional analysis of all Ironman triathlons held in 2010. Furthermore, this is in agreement with studies on marathon runners. In marathon running, both genders peak at a similar age of 29–30 years 2 5 . Up to now, only age group Ironman performances have been analyzed, with the best performances reached between 25 and 39 years for both genders 8 . In marathon running, the fastest times were achieved by athletes in the age groups between 20 and 39 years 13 23 , while ultra-runners seemed older, with the fastest age groups between 30 and 49 years 4 6 11 .

An important finding was that despite the unchanged age in peak Ironman performance, both women and men improved Ironman performance across years in Ironman Switzerland with a decrease in gender difference. From the beginning in 1995 to 2010, gender difference in overall race time decreased significantly, attended by an increasing female participation in Ironman Switzerland. While women improved overall race time by approximately 4 min annually, men improved by approximately 1 min annually over the last 16 years. In contrast, it has been shown that the gender difference in overall race times remained stable over the last two decades at the Ironman World Championship in Hawaii 18 .

The gender difference in overall race time of 15% for the overall top ten finishers in 2010 in Ironman Switzerland was slightly greater compared to the 13% in Ironman Hawaii (Table 2). This smaller gender difference in Ironman Hawaii is presumably because of the higher proportion of top athletes since Ironman Hawaii is held as the Ironman World Championship 21 . The top ten time spreads, i.e., the difference between the winner and the tenth placer is used to measure the extent of the highest level of competition 6 18 . The top ten time spreads for the overall top ten finishers in 2010 were less in Ironman Hawaii compared to Ironman Switzerland for both genders, but especially for women (Table 2). According to the slightly decreasing time spreads for female triathletes in Ironman Switzerland, the gender difference in overall race time is likely to come closer to those of Ironman Hawaii in the future.

Data from Ironman Hawaii 18 versus Ironman Switzerland for the overall top ten athletes in 2010.

Gender differences in physiological characteristics are likely to be the main factor for this gender difference in overall race time. Men have larger skeletal muscle mass 24 , correlating with greater muscular strength 16 , larger aerobic capacity 17 , and lower relative body fatness 25 26 27 compared to women. Low body fat is an important predictor variable for overall race time in an Ironman triathlon 28 . Low body fat was associated with faster race times in male Ironman triathletes 28 , while in female triathletes, anthropometric characteristics such as body fat seemed not to be related to Ironman race time 25 27 . However, women retain 7%–9% more percent body fat compared to men 25 26 , which is likely to be an advantage for men. Moreover, men probably have an advantage in muscular strength and aerobic capacity relative to the whole body mass 29 . Aerobic capacity is proportional to skeletal muscle mass, and both are strongly related to physical fitness 17 . Skeletal muscle mass is approximately 8% higher in male Ironman triathletes compared to female athletes, with 41.0 kg skeletal muscle mass in male versus 28.0 kg in female Ironman triathletes 17 . Aerobic capacity is approximately 14% higher in male Ironman triathletes, e.g., VO₂peak is 61.3 versus 52.8 ml/kg/min in men and women, respectively 17 .

Although the gender difference in swimming decreased over the last 16 years in Ironman Switzerland, the triathletes' swimming performance showed no changes. On the other hand, in Ironman Hawaii, the gender difference in swimming remained very similar over the last two decades 18 . In Ironman Hawaii, the mean gender difference in swimming was approximately 10%, while it was approximately 14% in Ironman Switzerland. The 10% difference in Ironman Hawaii is in agreement with other studies concerning gender difference in swimming performance 30 31 . However, there are two main differences between the swim split in Ironman Hawaii and in Ironman Switzerland. Firstly, it is prohibited to wear a wet suit in Ironman Hawaii because of the warm ocean water temperatures. However, athletes were allowed to wear a wet suit in Ironman Switzerland every year. Secondly, the swim in Ironman Hawaii is held in the ocean with salt water in contrast to Ironman Switzerland where the swim takes place in fresh water in Lake Zurich. These two factors are likely to explain the difference between the 14% gender gap in Ironman Switzerland and the 10% gap in Ironman Hawaii. It is well known that female triathletes have more body fat 25 26 . Wet suits increase swimming performance by increasing buoyancy where lean subjects, especially, may benefit more from wearing wet suits than fatter subjects 32 . On the other hand, women with more body fat may profit more from the denser salt water in the ocean 18 33 . Another reason for the greater gender difference in Ironman Switzerland might be the aforementioned lower proportion of top female triathletes.

Wearing a wet suit seems to improve swimming performance and cycling performance. Wearing a wet suit while swimming leads to a significantly lower swimming cadence (-14%), significantly lower heart rate (-11%), and significantly lower lactate values (-47%) compared to swimming without a wet suit 34 . Moreover, cycling efficiency in a triathlon was significantly higher (+12.1%) after swimming with a wet suit compared to swimming without a wet suit 34 . In an Ironman triathlon where athletes can wear a wet suit in the swim split, athletes without the background as a swimmer may profit from wearing a wet suit and achieve faster swim times. The background aspect of the triathlete also seems to be of importance. It has been reported that many triathletes were competitive swimmers 35 . Regarding recreational Ironman triathletes competing in a qualifier for Ironman Hawaii such as the Ironman Lanzarote, 28% of the athletes had a background as a runner, 14% as a swimmer, and 13% as a cyclist 22 . However, for elite Ironman triathletes competing in Ironman Hawaii, the history of the athletes has not been investigated yet. Athletes with a background as a swimmer may swim fast in open water in Ironman Hawaii independent of whether they wear a wet suit or not since they are used as swimmers to swim fast in contrast to a weak swimmer. It has been shown that wearing a wet suit improves swim performance more in inefficient swimmers with low buoyancy when swimming at low speeds 36 .

The annual top ten women and men improved cycling performance in Ironman Switzerland since 1995. Because of the greater improvement in women, the gender difference for the overall top ten finishers in 2010 in cycling has almost reached the level of Ironman Hawaii (Table 2). The mean gender difference in the 180-km cycling time trial is approximately 13%. Both cycling courses in Ironman Hawaii and Ironman Switzerland are relatively flat courses. In Ironman Hawaii, the altitude to climb is approximately 1,400 m, and in Ironman Switzerland, it is approximately 1,260 m. A comparison with other road cycling races is difficult because in these races the distances for women are shorter than those for men, and the races are generally held over shorter distances. For example, the pace difference between the first man and the first woman in the UCI Road World Championships in a time trial in 2010 held in Melbourne, Australia, was 11.4% (47.0 km/h versus 41.7 km/h). This 11.4% gender gap is likely to be underestimated because the distance for men was 45.8 km, but 22.8 km for women 37 . In track cycling, the gender difference is approximately 11% in race distances between 200 and 1,000 m 38 . Since this difference in cycling in Ironman Hawaii has increased over the last two decades 8 , but decreased in Ironman Switzerland, both gender differences in cycling have approached approximately 13%. Thus, we conclude that the gender difference in cycling in Ironman triathlon is at approximately 13%. Moreover, this gender difference in performance of 13% is close to the 11% and above in other cycling races. The main reason for this 11%–13% gender difference in cycling performance is the greater muscle mass of the lower extremities in men 29 .

Both women and men improved performance in the cycling split, but neither in the swimming nor in the running split. The improvement in the cycling split might explain the improvement in overall race time. We assume that Ironman triathletes invested more time in the preparation to improve in those split disciplines with more importance for the race. In an Ironman triathlon, the 3.8-km swim split accounts for only 1.7% of the total distance, whereas the 180-km cycling accounts for 79.6% and the marathon for 18.7% of the total race distance of 226 km. Recreational male Ironman triathletes invested 14.8 ± 3.2 h of training per week, and recreational female Ironman triathletes, 13.9 ± 3.4 h 26 . In men, swimming accounted for 2.5 h (16.9%), cycling for 8 h (54.0%), and running for 4 h (27.1%). Female Ironman triathletes invested 2.4 h in swimming (17.3%), 7.5 h in cycling (54.0%), and 4 h in running (28.8%).

Cycling performance can be improved by improvements in training and nutrition and alterations in equipment and seating position 39 . Factors such as aerodynamic accessories can modify the power demand in cycling 40 . Between 1995 and 2010, athletes may have improved both training and nutrition. Additionally, the bicycles and the aerodynamic accessories might have changed across years to improve cycling performance. All these improvements may have contributed to improved cycling performance and in the end an improved overall performance.

Running, along with cycling, is the most important discipline for a fast overall race time in a long-distance triathlon 41 . Women could have reduced the gender difference in marathon performance over the last 16 years in Ironman Switzerland, but there was no significant advance in running performance in either gender. On the other hand, women improved running performance by 3.8% per decade in Ironman Hawaii, with a relative improvement in running of 2.8% per decade for the top men 18 . The gender difference in running for the overall top ten finishers in 2010 in Ironman Switzerland was unexpectedly higher than that in Ironman Hawaii with approximately 18% in Ironman Switzerland and approximately 13% in Ironman Hawaii (Table 2). The gender difference in running in Ironman Hawaii is in line with the gender difference in top running events. Coast et al. compared the world's best running performances in distances between 100 m and 200 km 12 . The average gender difference was at 12.4% where longer distances were associated with greater gender differences 12 . In addition, the gender difference in performance in elite marathoners was approximately 12% 5 , and the gender difference between the top five women and men in the Western States 100-Mile Endurance Run in 2007 was 14% 6 .

However, the gender difference in running seemed to be higher if we focus not only on the top races but consider a wider range. Leyk et al. reported a 20% gap between the top ten male and female marathoners in 69 marathons in Germany 23 . The gender difference in the 100-km Lauf Biel was approximately 22% 4 . Hoffman reported that the fastest women were approximately 20% slower than the fastest men in all 161-km ultra-marathon competitions held in North America 11 . The difference of 14% in the gap in the Western States 100-Mile Endurance Run and approximately 20% in the other races is because the best times ever were achieved in the Western States 100-Mile Endurance Run, which is the oldest and most recognized 161-km running event 6 11 . We assume the same situation in Ironman triathlons with a smaller gender difference in Ironman Hawaii because this race is the Ironman Triathlon World Championship. These facts might be due to the lower proportion of top athletes, especially women, in Ironman Switzerland. In conclusion, we assume that the gender difference in running averages approximately 12%–14% in the premium running races and goes up to approximately 20% in a wider range of races. The effect of the smaller gender difference in top events compared with a wider range of events seems to be specific to running. Lepers and Maffiuletti compared the top ten amateur triathletes from nine age groups in Ironman Hawaii 8 . The difference was approximately 12% in swimming, approximately 15% in cycling, and approximately 18% in running for the 90 athletes of both sexes. There was a difference of approximately 2% in swimming and cycling compared to elite triathletes 18 , while the difference in running was approximately 5% higher for the 90 amateur triathletes. In swimming, women may profit from their better economy compared to men 42 . In cycling, the muscular advantage of men is proportional to skeletal muscle mass, and it is even greater in running 29 , where running is the only weight bearing activity where greater body fat is a limitation 25 26 . These are likely to be the reasons for the higher gender difference in running compared with cycling and swimming in a qualifying event for Ironman Hawaii. We assume that only the world's best women can overcome this disadvantage in running and that the top women in Ironman Switzerland have the best chance of improving their overall race time by improving their running performance.

A limitation of the present study is that only split times and overall race times, age, and gender of the Ironman triathletes were analyzed. Other performance-related factors such as years of training and training volume 25 26 , pre-race experience 25 43 , metabolic factors, technical constraints, performance-enhancing drugs 18 , and anthropometry 25 26 27 28 41 were not included. Regarding training and pre-race experience, training volume, cycling distance during training, speed in running during training, and both personal best marathon time and personal best time in an Olympic distance triathlon, were related to Ironman race time 22 25 26 43 44 . Furthermore, ultra-endurance performances such as an Ironman performance are influenced by weather conditions such as temperature, wind direction and velocity, rain, and water temperature 45 . The cycling performance depends on wind and weather conditions 18 . All these facts may influence performances, and they may limit comparison over the years. As the conditions in Ironman competitions are the same for every athlete, they do not influence the differences between the athletes, and there is no cause to assume that these facts influence the gender difference 18 . Concerning the difference between Ironman Switzerland and Ironman Hawaii, it should be mentioned that the weather conditions are different. Hawaii's climate is tropical in October when the Ironman takes place, i.e., approximately 30°C and approximately 70% humidity 46 . On the other hand, the climate in July is colder in Zurich, i.e., 20°C–25°C with humidity of approximately 70%. Wegelin and Hoffman reported that female performances were less affected by warm water than male performance 45 . The possibility of wearing a wet suit and the fresh water in Ironman Switzerland differs from Hawaii, while the cycling and running courses do not seem to be very different.