Warmer weather negatively impacts the finishing time of slower marathon (42.2 km) runners more than faster runners. How warmer weather impacts runners' regulation of effort (pacing) leading to the decreased performance is poorly understood.
Purpose: To determine the influence of air temperature on pacing of runners with differing abilities throughout the marathon.
Methods: Race results were obtained from three Japanese Women's championship marathons that included 5 km times, finishing time, and corresponding weather conditions. A total of 62 race years' outcomes were analyzed using the race winner and 25th, 50th, and 100th place finishers.
Results: The fastest marathoners (winners) ran an even pace throughout the race while runners of lesser ability slowed as the race progressed, particularly after 20-25 km. The difference between the first (0-5 km) and last (35-40 km) 5-km split times (pace differential) for the 100th place finishers was the same in cool (C = 5-10°C) as warm (W = 15.1-21°C) conditions (C = 199 ± 45 s; W = 198 ± 40 s). The pace differential for the 50th place finisher tended to increase with increasing air temperature (C = 115 ± 16 s; W = 16 3± 27 s) but was not significantly different. In contrast, warmer weather resulted in a slowing (P < 0.05) of pace for the 25th place finisher (C = 90 ± 25 s; W = 191 ± 20 s) and race winners (C = −22 ± 14 s; W = 24 ± 13 s).
Conclusions: Increasing air temperatures slow pace more in faster runners (winner, 25th) than slower runners (50th, 100th). These results suggest that the negative effect of warmer weather on the finishing times of slower runners is due to slower running velocities from start to finish, rather than a greater deceleration in pace which is exhibited by faster runners.