There exists a popular notion that cloud cover and/or low solar radiation increase the likelihood of running a fast marathon. This information can be found in anecdotal reports, authoritative reference books for runners, and scientific publications alike, but it lacks a comprehensive review. Purpose: 1) To determine whether the presence of cloud cover or low solar load are associated with fast marathons, 2) to describe the weather conditions during fast marathons, and 3) to determine whether the fastest men's and women's marathons are run in similar conditions. Methods: Finishing times and weather conditions were obtained for the winning performances of seven North American marathons, the 10 all-time fastest marathon times, world record marathons (WR), and Olympic Marathons for men (M) and women (F). Results: Cloud cover was not associated with a fast marathon race when odds ratios were calculated using the entire data set (0.68 (M); 0.51 (F)) or restricted to the 5-15[degrees]C ambient temperature (Tdb) range associated with fast race performances (0.42 (M); 0.43 (F)). Low solar load conditions also were not associated using the complete data set (1.4 (M); 1.3 (F)) or when restricted to the 5-15°C range (2.25 (M); 1.1 (F)). The common factor among fast performances has been low Tdb (10.6-12.8[degrees]C (M); 11.6-13.6°C (F)). In addition, neither cloud cover nor solar load were associated with top 10 or WR performances, because performances occurred in all cloud cover and solar load conditions. Conclusion: The presence of cloud cover or low solar load does not increase the likelihood of running a fast marathon. The prevailing temperatures during the fastest marathons (~12°C) corroborate previous assertions and seem similar for men and women.
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