The Short Answer
Multiday running exposes the body to prolonged load, sleep loss, environmental stress, and a sustained gap between energy use and intake. Many runners finish without a serious medical event, but good preparation does not make the activity harmless. Individual health, event length, weather, pace, medication use, and access to medical care all change the risk.
Common Risks and How They're Managed
| Risk | What We Know | Risk Reduction |
|---|---|---|
| Feet and skin | Hot spots and blisters are common; broken skin can become infected | Test footwear and socks, address pressure early, and use race foot-care support |
| GI symptoms | Nausea, bloating, diarrhea, or vomiting can limit intake; persistent symptoms are not always benign | Practice fueling, reduce effort when symptoms start, and seek help if fluids will not stay down |
| Muscles, tendons, and bones | Soreness is expected; focal injury, stress injury, and rhabdomyolysis can occur | Build load gradually, pace conservatively, and stop for worsening focal pain or altered gait |
| Fluid and sodium disorders | Both heat-related dehydration and overdrinking-related hyponatremia can be dangerous | Use thirst as the starting signal, avoid forced drinking, and remember that sodium does not make overdrinking safe |
| Kidney or cardiac problems | Post-race markers often change, but symptoms or severe abnormalities require assessment | Discuss relevant history with a clinician and avoid self-medicating with NSAIDs during the race |
Long-Term Health Profile
Long-term evidence is limited. The observational ULTRA Study baseline report found generally favorable health characteristics in a selected group of active ultrarunners, but it was retrospective, self-reported, and not proof that ultrarunning caused those outcomes. A later review of potential long-term effects concluded that cumulative cardiac, renal, musculoskeletal, and other effects remain under-studied. Acute biomarker changes often improve after an event, but a blood-test timeline alone cannot rule out injury in a symptomatic runner.
How to Make It Safe
Build an adequate training base, choose well-organized races with medical support, practice your nutrition strategy before race day, use thirst rather than a forced drinking schedule, and know when to stop. Ask a sports medicine clinician about participation if you have exertional chest pain, unexplained fainting, known heart or kidney disease, a prior heat illness or sodium disorder, or medicines that affect fluid balance.
Sources
- Hoffman, M.D. (2016) — "Injuries and Health Considerations in Ultramarathon Runners." Physical Medicine and Rehabilitation Clinics of North America, 27(1), 203–216.
- Scheer, V. et al. (2022) — "Potential Long-Term Health Problems Associated with Ultra-Endurance Running: A Narrative Review." Sports Medicine, 52(4), 725–740.
- Hew-Butler, T. et al. (2015) — Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clinical Journal of Sport Medicine, 25(4), 303–320.
- Hoffman, M.D. & Krishnan, E. (2014) — "Health and Exercise-Related Medical Issues among 1,212 Ultramarathon Runners." PLoS ONE, 9(1), e83867.