Research Variables
This paper defined peak performance characteristics as the age of peak performance and the window of peak performance. The age of peak performance indicated the age at which an athlete achieved their career-best performance.[4] The window of peak performance described the period during which the athlete maintained their career-best performance.[4]
The study investigated the key factors in development for achieving better peak performance among world elite speed skaters through various competitive feature variables. The competitive feature variables included first participation age (FPA), first major competition age (FMA), career-best performance age (CPA), first participation performance (FPP), first major competition performance (FMP), career-best performance (CBP), participation frequency in phase-1 (PF1), participation frequency in phase-2 (PF2), participation frequency in phase-3 (PF3), and athletic career length (ACL). The descriptive statistical results and their definition for the above variables were presented in Table 1.
Data Sample and Outliers
The world elite speed skaters were defined as athletes who had achieved top-10 position in individual events at the Winter Olympic Games or World Single Distance Speed Skating Championships. The competition performance data of the speed skaters were sourced from the official database of the International Skating Union (ISU), which provided detailed records of each speed skater's name, age, competition date, competition name, and venue where the result was set. The dataset covered the seasons from 2003/2004 to 2022/2023 and included results generated by timekeeping system. Excluded from the dataset were the World Sprint Speed Skating Championships and World Allround Speed Skating Championships due to differing competition rules compared to the Winter Olympic Games. Consequently, the dataset comprised 4 Winter Olympic Games (Due to the absence of competition data from the 2006 Turin Winter Olympic Games in the database, the data were excluded), 151 World Cup, and 37 World Championships (including the World Single Distance Speed Skating Championships, ISU Four Continents Speed Skating Championships, ISU European Speed Skating Championships, and World Junior Speed Skating Championships), totaling 192 competitions. Based on the competition distances,[24] this study categorized speed skating events into 3 groups: sprint events (500-1000m for both males and females), middle-distance events (1500-m for both males and females), and distance events (5000-10000m for males; 3000-5000m for females), covering a total of 10 individual events across these categories.
During data collection and sample selection, four types of exceptional cases were excluded: 1) Outliers with performance times exceeding 4.5 standard deviations, as per Hopkins et al.[25], were removed. 2) Athletes whose performance trajectories did not follow a parabolic curve, rising to a peak and then declining, were excluded.[23] This was determined by fitting developmental curves, and samples deviating from this pattern were discarded. Additionally, samples with peak ages outside the athletes' competition years were removed to reduce research bias.[4] 3) Athletes still active at the end of the 2020/2021 season, when international events were suspended due to the pandemic, were excluded from participation frequency analysis.[12] 4) Athletes whose first major competition occurred before their first participation age or whose career-best performance predated their first major competition were excluded from the phase-1 and phase-2 participation frequency analyses, respectively. After processing, the final sample comprised 651 athletes and 46,986 competition records.
Statistical Analysis
All statistical analyses in this study were conducted using SPSS ver. 25. For characteristics of peak performance, Figure 1 illustrated how a quadratic curve model was used to determine an athlete's peak age and calculate the duration of peak-performance window. The quadratic curve model used to fit the performance trajectory of an athlete's was: y=a×Age2+b×Age+c. Each athlete's performance trajectory was individually derived. The formula to describe the peak age was -b/(2a), and the formula to describe the duration of the peak-performance window was 2(√∆/a), where ∆ was the smallest worthwhile change in performance. The calculation of ∆ value was based on the study by Noordhof et al.[26], which multiplied the coefficient of variation of each event by their corresponding smallest worthwhile effects. The smallest worthwhile effects was calculated as 0.3 of the within-athlete variation in performance between international competitions.[27] For males, values for within-athlete variation were 0.6% for ≤1000-m events, 0.5% for 1500-m, 0.8% for 5000-m, and 1.2% for 10000-m. For females, the coefficient of variation were 0.8% for ≤1000-m events, 0.7% for 1500-m, 0.9% for 3000-m, and 1.1% for 5000-m. Consequently, the ∆ values for male's events were 0.18%, 0.15%, 0.24%, and 0.36%, respectively, while for females's events, they were 0.24%, 0.21%, 0.27%, and 0.33%, respectively. Additionally, the Mann-Whitney U test was conducted to investigate differences in characteristics of peak performance. In brief, when the effect size (Z-value) of the significance test lay within -2.58≤Z<-1.96 and Z<-2.58, the corresponding significance levels of the differences were P<0.05 and P<0.01, respectively. Based on whether elite speed skaters had won medals at the Winter Olympic Games or World Single Distance Speed Skating Championships, this study divided the sample into two subgroups: medalists and non-medalists, to explore differences in peak age and window of peak performance between them.
To explore the key developmental factors, competitive feature variables were clustered using k-means, with those showing significant differences between clusters selected as independent variables and career-best performance (CBP) as the dependent variable.[12] The nine competitive feature variables were grouped into three categories, while the CBP was divided into two. A one-way analysis of variance revealed significant differences among the groups (P<0.01). Consequently, the nine variables, along with gender, nationality, and competition distance as control variables, were included as independent variables, with CBP as the dependent variable. To further analyze key developmental factors, the study incorporated the odds ratio (OR) into the regression model. OR, calculated as the exponential of the coefficient (OR=eβ), measured the correlation between variables: OR>1 indicated a favorable factor, OR<1 an unfavorable one, and OR=1 no association between the variables.
Data Processing
During the statistical analysis, it was found that most elite speed skaters had participated in multiple events. When analyzing individual events separately, the data for secondary-events (individual events aside from the primary-event) were often insufficient, making it difficult to accurately reflect the characteristics of peak performance and developmental key factors of the athletes. Therefore, the study concluded that it was inappropriate to analyze secondary-events separately. Additionally, this study focused on athletes who had ranked in the top-10 at the Winter Olympic Games or World Single Distance Speed Skating Championships. However, the dataset included all performance data from the athletes' careers, which might have meant that some athletes' secondary-events performances did not reach elite levels. Consequently, for athletes participating in multiple events, the event in which they achieved their best performance was considered their primary-event, while other events were considered secondary-events. Although secondary-events were not analyzed separately in the statistical process, their data were retained and included in the analysis of primary-event.
Due to significant performance differences between different speed skating events, a normalization method was adopted to standardize the performance time of primary- and secondary-events. Drawing from related research in swimming, the study converted performance time into competitive points for horizontal and vertical comparisons.[12] The formula for calculating competitive points was P=100×(B/T)3, where B was the benchmark time for the specific event (world record performance) and T was the athlete's competition time for that event. Through the conversion formula, each points value corresponded to a specific performance in an event. Given the minimal performance improvements in speed skating from the 2003/2004 to 2022/2023 seasons, the potential impact of time series was excluded.[28] Subsequently, we utilized the formula to convert the transformed points for the analysis of speed skaters' peak performance characteristics.