What is an ergogenic aid?
Anything that improves performance — substance, technique or equipment. The category spans well-evidenced interventions like caffeine and carbon-plate shoes and a great deal that does not survive scrutiny.
An ergogenic aid is any substance, method or device intended to enhance performance. That definition is broad enough to include nutritional strategies such as carbohydrate loading, pharmacological aids such as caffeine, mechanical aids such as carbon-plated racing shoes, and environmental methods such as heat or altitude acclimation.
For distance running, the interventions with the strongest evidence are unglamorous and few: carbohydrate intake during long events, caffeine at 3–6 mg/kg, modern racing footwear, and heat acclimation for hot races. Between them these account for most of the legitimate marginal gains available, and each has effect sizes measured in low single-digit percentages.
It is worth calibrating against that. A 2–4% gain from caffeine is real and worth having, and it is also smaller than the difference a year of consistent training makes. Marginal gains are marginal by definition, and they only matter once the fundamentals — volume, consistency, sleep, fuelling — are actually in place.
Most of what is marketed to runners does not clear this bar. The useful test for any claimed aid is whether controlled trials show an effect in trained athletes at realistic doses, and whether the effect size survives publication bias. A great many popular supplements fail that test quietly.
Key numbers
| Caffeine | 2–4% | well-evidenced |
|---|---|---|
| Racing shoes | ~4% economy | well-evidenced, variable |
| Heat acclimation | 2–7% | small studies |
Work it out for yourself
Caffeine & stimulants model — Model the ergogenic aids this site actually implements, with their evidence stated.
Frequently asked questions
What is the most effective legal ergogenic aid for runners?
Caffeine and modern racing footwear have the strongest evidence, each in the low single-digit percentages. Carbohydrate intake during the race is arguably larger still for the marathon specifically, since it prevents a failure rather than delivering an increment.
Are supplements worth it for distance runners?
Most are not. Beyond correcting an actual deficiency — iron and vitamin D are the ones worth testing for — the supplement market has very little that survives controlled testing in trained athletes at realistic doses.
Sources
- Southward, Rutherfurd-Markwick & Ali (2018). The effect of acute caffeine ingestion on endurance performance. Sports Medicine.
- Hoogkamer et al. (2018). A comparison of the energetic cost of running in marathon racing shoes. Sports Medicine.
Related explainers
Glossary: Ergogenic Aid