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Age of peak performance in elite male and female Ironman triathletes competing in Ironman Switzerland, a qualifier for the Ironman world championship, Ironman Hawaii, from 1995 to 2011

Background The age of peak performance in elite endurance athletes has been investigated for elite marathoners, but not for elite Ironman triathletes. The aim of this study was to analyze the age of peak performance in swimming (3.8 km), cycling (180 km), running (42 km), and overall race time for elite female and male Ironman triathletes competing in Ironman Switzerland, a qualifier for the Ironman world championship, known as the Ironman Hawaii. Methods The age of the annual top ten overall swimmers, cyclists, runners, and annual overall finishers for both male and female elite triathletes and their corresponding split and overall race times at the Ironman Switzerland were analyzed between 1995 and 2011. Results The mean age of the elite Ironman triathletes was 33 ± 3 years for men and 34 ± 4 years for women. For women, the age of peak performance was not significantly different between the three disciplines (P > 0.05), while for men, the best swimmers (29 ± 3 years) were significantly (P < 0.05) younger than the best runners (35 ± 5 years). During the study period, the age of peak performance remained unchanged for men at 31 ± 3 years (P > 0.05), but increased for women from 30 ± 4 years in 1995 to 36 ± 5 years in 2011 (P < 0.01). Conclusion Although both women and men improved their overall race times during the 1995–2011 period, the age of peak performance was similar between women and men in the three disciplines and in overall race time. Future studies need to examine the change in age of peak performance across years in the Ironman Hawaii world championship event.


Introduction
An age-related decline in performance has been described for different endurance disciplines, including swimming, 1-3 running, [4][5][6] and multisports disciplines such as the duathlon 7 and triathlon over different distances. [8][9][10][11][12][13][14][15] Generally, endurance performance peaks between 35 and 40 years. 2,3 After the age of 40-50 years, endurance performance starts to decrease. 2,3,6 This lowering in performance is moderate until the age of 70 years, after which the decrease in endurance performance becomes exponential. 2,3 Regarding the triathlon, age-related decline in performance has been investigated for the short or Olympic distance triathlon (1.5 km swimming, 40 km cycling, and 10 km running), 8 the half-Ironman triathlon (1.9 km swimming, 90 km cycling, and 21.1 km running), 15 and the Ironman triathlon (3.8 km swimming, 180 km cycling, and 42.195 km running). [9][10][11][12][13] The age-related decrement in triathlon performance is specific to the discipline, with cycling showing a slower regression in performance with age than swimming and running. 8,10,14 For elite athletes, the age of peak performance 15,16 is probably of higher interest than the age-related decline in performance [8][9][10][11][12][13][14] or the performance of master athletes. 12,13 For example, knowing the age of the best endurance performance can be useful in a sports career when it comes to planning highlights such as the Olympic Games or the world championships for elite athletes. Regarding the existing literature for endurance athletes, the age of peak performance for elite athletes appears to be different between different endurance disciplines. For elite swimmers, Schulz and Curnow described the age of peak performance as being about 20 years. 16 In contrast, the age of peak performance for elite marathoners was reported to be approximately 28 years 16 and 30 years. 17 Female triathletes competing in the half-Ironman achieved their fastest race times at the age of 25-39 years whereas male triathletes were fastest at the age of 18-39 years. 15 For mountain ultramarathoners, top female runners achieved their fastest race time at 34.4 ± 2.5 years and top male runners at 33.9 ± 4.2 years. 18 For the Ironman triathlon, recent studies reported that master athletes increased their participation and improved their performance across years. 12,13 In addition, Lepers and Maffiuletti reported that the fastest Ironman race times were achieved in the age groups 30-34 years and 35-39 years for men and 25-29 years and 30-34 years for women. 11 However, no study has investigated the age of peak performance for elite Ironman triathletes in contrast with elite marathoners. 17 The aim of the present study was to analyze the age of peak performance in swimming, cycling, and running, as well as overall race time for both elite male and female Ironman triathletes. Given that Ironman triathletes have to run a marathon at the end of the race, we hypothesized that the age of peak performance would be close to 30 years for both female and male elite Ironman triathletes, as had been previously reported for elite marathoners. 17 Considering the fact that the age of peak performance differed between elite swimmers 16 and elite marathoners, 17 one might assume that the age of peak performance would be different between the three split disciplines in an Ironman triathlon. We also hypothesized that the fastest swimmers would be younger than the fastest marathoners in an Ironman triathlon.

Materials and methods
The changes in age and both split and overall race times of all triathletes finishing Ironman Switzerland between 1995 and 2011 were analyzed. The data set from this study was obtained from the Ironman Switzerland race website. 19 The study was approved by the institutional review board of St Gallen, Switzerland, with a waiver of the requirement for informed consent, given that the study involved analysis of publicly available data.
Data from 19,389 athletes, including 2051 women and 17,338 men who successfully finished Ironman Switzerland between 1995 and 2011, were available and could be included in the analysis. The age and performance of the ten fastest women and men for overall finishers as well as the ten fastest women and men in the three disciplines of swimming, cycling, and running were determined for each year (i.e. 17 years of duration, 4 times (3 split times and overall race time), 2 genders, and 10 athletes (top ten athletes) leads to n = 17 × 4 × 2 × 10 = 1360).

Statistical analysis
In order to increase the reliability of data analysis, each set of data was tested for homogeneity of variance prior to statistical analysis using Levene's test in the event of two groups and Bartlett's test in the event of more than two groups. Linear regression was used to test for significant changes in the variable over the years of the study. To detect differences between two groups, a Student's t-test was used, and one-way analysis of variance with subsequent Tukey-Kramer post hoc analysis was performed to find differences between more than two groups. To identify differences between the ages of peak performance in the different disciplines, a year-by-year analysis was performed using a two-way analysis of variance with subsequent Bonferroni post hoc analysis. Statistical analyses were performed using the Statistical Package for the Social Sciences version 19 (SPSS Inc, Chicago, IL) and GraphPad Prism (Version 5, GraphPad Software, La Jolla, CA). Statistical significance was accepted at P , 0.05 (two-sided for t-tests). Data in the text are given as the mean ± standard deviation.

Results
During the 17 years from 1995 to 2011, a total of 19,389 athletes completed Ironman Switzerland. Women accounted for 10.6% of all finishers. During the study period, the participation of both women and men increased ( Figure 1). In 1995, 15 women and 174 men finished, whereas in 2011, 204 women (+1260%) and 1398 men (+703%) finished.
Regarding the ten overall fastest women over the 17-year period (Table 1), the age of peak performance was not significantly different between the three split disciplines and overall race time. The top ten male swimmers were aged submit your manuscript | www.dovepress.com Dovepress Dovepress 29 ± 3 years and were significantly (P , 0.05) younger than the top ten male runners who were aged 35 ± 5 years. The overall top ten women and men showed no difference in age of peak performance in any of the split times or overall race time (P . 0.05). Figure 2 shows the development of overall race time (A) and age (B) across years for both women and men. The overall top ten women improved their overall race time significantly (P , 0.01) by 12.7% from 678 ± 34 minutes in 1995 to 592 ± 27 minutes in 2011. The overall top ten men improved their overall race time significantly (P = 0.03) by 6.4% from 559 ± 15 minutes in 1995 to 523 ± 15 minutes in 2011. During the 1995-2011 period, the age of the top ten women increased significantly (P , 0.01) from 30 ± 4 years in 1995 to 36 ± 5 years in 2011. However, the mean age of the top ten men remained unchanged (P . 0.05) at 31 ± 3 years.
In swimming, the top ten female swimmers improved their split time significantly (P = 0.04) over the 17-year period by 20.3%, from 74 ± 5 minutes in 1995 to 59 ± 3 minutes in 2011 ( Figure 3A). The age of the top ten female swimmers increased significantly (P , 0.01) by 16.7% across the years from 30 ± 3 years in 1995 to 35 ± 4 years in 2011 ( Figure 4A). In contrast, the top ten male swimmers did not improve (P . 0.05) their swim time across the years (47 ± 1 minutes). The mean age of the male top ten swimmers remained stable (P . 0.05) at 30 ± 5 years.
For cycling, the top ten women improved their split time significantly (P , 0.01) by 12.4% from 364 ± 15 minutes to 319 ± 13 minutes ( Figure 3B). The top ten men also improved their cycling time significantly (P , 0.01) by 7.7% from 312 ± 7 minutes to 288 ± 7 minutes over the years of the study. The age of the top ten cyclists increased significantly (P , 0.01) by 13.3% for women, from 30 ± 4 years in 1995 to 34 ± 4 years in 2011, and significantly (P , 0.01) by 6.5% for men, from 31 ± 4 years in 1995 to 33 ± 6 years in 2011 ( Figure 4B).
The top ten female runners improved their marathon time significantly (P , 0.05) by 14.5%, from 235 ± 19 minutes in 1995 to 201 ± 10 minutes in 2011 ( Figure 3C). The ten fastest male running times remained unchanged (P . 0.05) at 161 ± 2 minutes. The age of the top ten female marathoners increased significantly (P , 0.01) by 6.5%, from 31 ± 5 years in 1995 to 33 ± 7 years in 2011 ( Figure 4C). In contrast, the age of the top ten male marathoners remained unchanged (P . 0.05) at 31 ± 4 years.

Discussion
This study analyzed the age of peak performance in swimming, cycling, and running, as well as overall race time for male and female elite Ironman triathletes competing in Ironman Switzerland, a qualifier for Ironman Hawaii. It was hypothesized that the age of peak performance would be close to 30 years for both female and male elite Ironman triathletes. The results show that the age of peak performance of approximately 33-34 years was not different between women and men. Elite male marathoners were about 3 years younger and elite female marathoners about 4 years younger than the present elite Ironman triathletes. 17 This finding suggests that elite Ironman triathletes need more experience than marathoners to perform at a high level. It has been shown that a fast personal best marathon time was a strong predictor variable for a fast Ironman race time for both male 20,21 and female 22 Ironman triathletes. Elite Ironman triathletes probably need time to gain adequate experience for a fast Ironman race time. Furthermore, the Ironman triathlon is not an Olympic event, so the athlete profile may be influenced by this fact. Taking in consideration that many grants and financial considerations arise for athletes when they are competing in an Olympic event for their country, at this   During the study period, the age of the top ten female triathletes increased from 30 ± 4 years in 1995 to 36 ± 5 years in 2011, whereas the age of the top ten male triathletes remained unchanged at 31 ± 3 years. Although the age of elite women increased, they improved their overall race time. Similarly, the age of both the top ten female swimmers and the top ten female marathoners increased, although they became faster. However, these trends were not observed for men. An important aspect is the low female participation in the Ironman triathlon. 9 Although female submit your manuscript | www.dovepress.com Dovepress Dovepress participation in Ironman Switzerland has increased over the years, women accounted for only 10.6% of finishers. Generally, participation of women in ultraendurance distances is very low compared with men. 9,[23][24][25] We assume that the increase in age and improvement in performance for elite female triathletes might be explained by both motivational and social factors. Most probably, women have a different approach to ultraendurance performance, which is also reflected in the rather low female participation. Considering the motivation of women participating in ultraendurance performance, Krouse et al described female ultramarathoners as task-oriented, internally motivated, healthy, and financially aware individuals. 26 Familiar social factors might also be considered as an explanation for the findings in women. Ironman Switzerland is dominated by Swiss and German triathletes. 27 The mean age of Swiss women at birth of their first child has increased since 1975. The age at first birth was 30.7 years in 2006 and increased to 31.2 years in 2010. 28 After the age of 44 years, a significant increased incidence of cesarean section, pregnancy-induced hypertension, gestational diabetes, and perinatal mortality has been reported. 29 Race preparation is another aspect that needs consideration. Both female and male Ironman triathletes need time to train. 30 Elite female athletes might have either borne children or remained childless and worked. A woman occupied with both family and a part-time job would not have enough time to train seriously for an Ironman triathlon. Given that both a fast personal best time in an Olympic distance triathlon and in a marathon were strong predictor variables for female Ironman triathletes, 22 elite female Ironman triathletes would need time to gain experience in both the triathlon and marathon to achieve the level of an elite Ironman triathlete. This might explain the increase in the age of peak performance across years. It would be interesting to examine further the effect of family status on the performance of elite female triathletes.
Between 1995 and 2011, both the top ten women and the top ten men improved their overall race time, with a greater percentage of women improving than men. In addition, the top ten women improved their split times in the three disciplines, whereas the top ten men improved their cycling time. We found a faster race time in 1996 and 2000 compared with the preceding year. Olympic Games were held in 1996 in Atlanta and in 2000 in Sydney. Most likely, it was a coincidence that fast Ironman race times were achieved in these years. Improvements in the bike split for both genders are likely due to the development of technical equipment over the years. During an Ironman triathlon, drafting is forbidden 31 and aerodynamic resistance is the major resistance force the racing cyclists must overcome. 32 The configuration of the bicycle and body position during cycling are important factors for a fast cycling time in a nondrafting race. 33 During the time period 1995-2011, women had probably the same access to race bikes as men. Therefore, reasons other than technical aspects, such as anthropometric characteristics, 34 might be needed to explain the difference between men and women.
An important finding was that the age of peak performance was younger for the best swimmers than for the best runners in men but not in women. The age of peak swim performance has been investigated in freestyle swimmers for distances ranging from 50 m to 1500 m and also for ultradistances. The age of peak swim performance seems to depend upon both gender and swim distance. 3,16,[35][36][37] The age of peak swim performance was reported to be about 21 years by Berthelot et al when 12 events were chosen in long-course pool freestyle swimming (ie, 50 m, 100 m, 200 m, 400 m, 800 m, and 1500 m for women and men). 35 However, other authors have reported different results. Fairbrother reported that the age of peak swim performance in men for 50 m freestyle was achieved in the late 20 s and early 30 s. 37 Tanaka and Seals showed that peak swim performance in 50 m freestyle was reached at the age of 20-30 years in both men and women. 3 However, for ultraswimmers, the best performance was reached in the age group 30-39 years by both women and men in a 12-hour indoor ultraswimming event. 36 These contrasting findings might be due to the different swim distances examined. Some studies have suggested that a difference may exist in the age of peak swim performance with regard to both swim distance and gender. 3, 16 Schulz and Curnow reported that women generally reached their peak swim performance at younger ages than men, especially for long freestyle distances such as the 800 m and 1500 m. 16 These authors showed that, for freestyle swimming in Olympic Gold medalists in the 1896-1980 period, the age of peak freestyle performance for men was about 21 years for 100 m, about 20 years for the 400 m, and about 20 years for the 1500 m, respectively. 16 For women, the peak swim performance was attained at approximately 19 years for the 100 m, at about 18 years for the 400 m, and at about 16 years for the 800 m. 16 In contrast with these findings, Tanaka and Seals reported that for the 1500 m freestyle, men reached their fastest swim times at the age of 25-40 years, while women achieved their best performance at the age of 30-35 years. 3 For the shorter distances, peak swim performance for the 50 m was attained at the age of 20-30 years for both women and men. 3 For runners, the age of peak performance increased with race distance (ie, 100-800 m) for both women and men, and women generally achieved their peak performance at a younger age. 16 However, in elite marathoners, women achieved peak performance at an older age than men. 17 The difference in performance might also be explained by anthropometric characteristics, such as skeletal muscle mass. It has been argued that the increase in gender differences in performance with increasing length of an ultratriathlon could be due to the lower skeletal muscle mass in women compared with men. 24 Male ultraendurance athletes generally have a higher skeletal muscle mass than their female counterparts. 34,38,39 In male Ironman triathletes, skeletal muscle mass amounted to about 41 kg, which was about 46% higher than the nearly 28 kg of skeletal muscle mass in female Ironman triathletes. 39 For ultrarunners, men with approximately 38 kg skeletal muscle mass 40 had a nearly 38% higher muscle mass compared with women, who had about 27.4 kg. 41 In ultraswimmers, the gender difference in skeletal muscle mass was considerably higher. 42 Men with about 42 kg of skeletal muscle mass had nearly 45% more skeletal muscle mass compared with women having a skeletal muscle mass of 29 kg. The higher skeletal muscle mass in men might be an important variable in performance for ultraendurance athletes. The difference in muscle strength between trained women and men can be explained by the size of the muscle mass and not by differences in muscle fiber type or muscle adaptation. 43 Women with a lower lean leg volume developed lower peak power compared with men. 44 This study is limited due to the large difference in athletic performance between men and women, which might have influenced the data analysis. Data on anthropometry, 21,[45][46][47][48][49] training, 21,45,47,49 previous experience, 21,49,50 nutrition, 51,52 and nationality of the athletes 27 were lacking, and might have had an influence on race outcome.

Conclusion
The age of peak overall performance of about 33-34 years was not different between male and female elite Ironman submit your manuscript | www.dovepress.com Dovepress Dovepress triathletes, and seemed greater than the age of peak overall performance of marathoners. The age of peak performance was also similar between male and female triathletes in the three disciplines. The age of peak performance was younger for the best swimmers than for the best runners in men, but not in women, suggesting a high performance in endurance swimming might be obtained at a younger age compared with endurance running, at least in men. Future studies should examine the age of peak performance for other ultraendurance disciplines, along with the relationship between changes in age of peak performance over the years and changes in the age of the general population and demographics over the years. The age of peak performance in the Ironman world championship, ie, Ironman Hawaii, should also be investigated.

Disclosure
The authors report no conflicts of interest in this work.