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Carol A. Parise and Martin D. Hoffman


Even pacing has been recommended for optimal performances in running distances up to 100 km. Trail ultramarathons traverse varied terrain, which does not allow for even pacing.


This study examined differences in how runners of various abilities paced their efforts in the Western States Endurance Run (WSER), a 161 km trail ultramarathon in North America, under hot vs cooler temperatures.


Temperatures in 2006 (hot) and 2007 (cooler) ranged from 7-38°C and 2-30°C, respectively. Arrival times at 13 checkpoints were recorded for 50 runners who finished the race in both years. After stratification into three groups based on finish time in 2007 (<22, 22-24, 24-30 h), paired t tests were used to compare the difference in pace across checkpoints between the years within each group. The χ2 test was used to compare differences between the groups on the number of segments run slower in the hot vs cooler years.


For all groups, mean pace across the entire 161 km race was slower in 2006 than in 2007 (9:23 ± 1:13 min/km vs 8:42 ± 1:15 min/km, P < .001) and the pace was slower from the start of the race when temperatures were still relatively cool. Overall, the <22 h cohort ran slower in 2006 than 2007 over 12 of the 14 segments examined, the 22–24 h cohort was slower across 10 of the segments, and the >24 h cohort was slower across only 6 of the segments χ2 2 = 6.00, P = .050). Comparable pacing between the 2 y corresponded with onset of nighttime and cooling temperatures.


Extreme heat impairs all runners’ ability to perform in 161 km ultramarathons, but faster runners are at a greater disadvantage compared with slower competitors because they complete a greater proportion of the race in the hotter conditions.

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Martin D. Hoffman and Carol A. Parise


This work longitudinally assesses the influence of aging and experience on time to complete 161-km ultramarathons.


From 29,331 finishes by 4066 runners who had completed 3 or more 161-km ultramarathons in North America from 1974 through 2010, independent cohorts of men (n = 3,092), women (n = 717), and top-performing men (n = 257) based on age-group finish place were identified. Linear mixed-effects regression was used to assess the effects of aging and previous 161-km finish number on finish time adjusted for the random effects of runner, event, and year.


Men and women up to 38 y of age slowed by 0.05–0.06 h/y with advancing age. Men slowed 0.17 h/y from 38 through 50 y and 0.23 h/y after 50 y. Women slowed 0.20–0.23 h/y with advancing age from 38 y. Top-performing men under 38 y did not slow with increasing age but slowed by 0.26 and 0.39 h/y from 38 through 50 y and after 50 y, respectively. Finish number was inversely associated with finish time for all 3 cohorts. A 10th or higher finish was 1.3, 1.7, and almost 3 h faster than a first finish for men, women, and top-performing men, respectively.


High-level performances in 161-km ultramarathoners can be sustained late into the 4th decade of life, but subsequent aging is associated with declines in performance. Nevertheless, the adverse effects of aging on performance can be offset by greater experience in these events.