Last week I published my heat-adjusted pace calculator, which estimates how much you’ll have to slow down in hot, humid conditions during a long workout or long race in the heat.
The timing of the release provided a very nice opportunity for a validation test: the marathon at the 2025 World Athletics Championships, which was held this past weekend in brutally hot conditions in Tokyo.
The women’s race on Sunday was held in 86° F (30° C) and 70% humidity; the men’s race on Monday was held in 82° F (28° C) and 72% humidity. These, clearly, are far from ideal marathon conditions, and the finish times reflect the difficult conditions.
By looking at how slow the top athletes actually ran, compared with how slow they were predicted to run by my calculator, we can check how accurate these “heat-adjusted paces” really are.