Background: Pacing, defined as percentage changes of speed between successive splits, has been extensively studied in running and cycling endurance sports; however, less information about the trends in change of speed during cross-country(XC) ski racing is available. Therefore, the aim of the present study was to examine the effect of performance(quartiles of race time(Q), with Q1 the fastest and Q4 the slowest) level on pacing in the Vasaloppet ski race, the largest XC skiing race in the world.Methods: For this purpose, we analyzed female(n = 19,465) and male(n = 164,454) finishers in the Vasaloppet ski race from 2004 to 2017 using a one-way(2 sexes) analysis of variance with repeated measures to examine percentage changes of speed between 2 successive splits. Overall,the race consisted of 8 splits.Results: The race speeds of Q1, Q2, Q3, and Q4 were 13.6 § 1.8, 10.6 § 0.5, 9.2 § 0.3, and 8.1 § 0.4 km/h, respectively, among females and16.7 § 1.7, 13.1 § 0.7, 10.9 § 0.6, and 8.9 § 0.7 km/h, respectively, among males. The overall pacing strategy of finishers was variable. A small sex ￡ split interaction on speed was observed(h2= 0.016, p < 0.001), with speed difference between sexes ranging from 14.9%(Split 7) to27.0%(Split 1) and larger changes in speed between 2 successive splits being shown for females(p < 0.001, h2= 0.004). A large performance ￡ split interaction on speed, with Q1 presenting the smallest changes of speed between splits, was shown for females(h2= 0.149, p <0.001) and males(h2= 0.169, p < 0.001).Conclusion: Male and fast XC skiers are more even pacers. Coaches and athletes should develop tailored sex-and performance-level pacing strategies; for instance, they should advise fast XC skiers to start fast and maintain their speed, rather than starting slowly and trying to make up time by going faster at times during the race.
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