Pacing strategies are important factors for running performance and have been studied over the years. Nevertheless, whether the implementation of such strategies is crucial at ultramarathons under extreme weather conditions remains unclear. The purpose of this study was to investigate the use of running pace strategies in ultramarathons performed under very hot or cold weather conditions. Data from Desert Ultra 2022 and 2023 and Ice Ultra 2023 and 2024, each covering approximately 250 km during five consecutive days, were analyzed. Data from 143 runners included sex, finish time, pace, velocity, the number of runners who did not finish the ultramarathon, and the number of runners who did not start the ultramarathon. Participants were categorized into top 3, top 10, and top 20. Finish times were no equivalent between events (Ice Ultra; 43:47 ± 7:02 h:min vs. Desert Ultra; 48:10 ± 8:27 h:min; p = 0.002). The top 3 participants exhibited higher velocity in multiple stages compared with the other groups (p < 0.01). In top 20 runners, maintenance of the velocity pattern throughout the days was evident. However, the Ice Ultra group exhibited a decline in velocity between stages 1 and 2 (Δtop 3: 2.23 ± 0.14 km/h; Δtop 10: 2.11 ± 0.15 km/h; Δtop 20: 1.19 ± 0.18 km/h). Higher densities showed high heterogeneity among runners regardless of desert or ice running. Relief and weather are important factors in pacing strategies. Ice Ultra runners displayed a parabolic running strategy. In the Desert Ultra race, a substantial reduction in speed was observed even when there was no slope and even halfway through the completion of the pacing strategy stages. Managing fatigue from previous stages and temperature fluctuations are relevant factors that can be better explored.
