You cross the finish line. The race is over. Your body hasn't gotten the message yet.

For days afterward, your blood will show markers that look like something is wrong. Because something is. Here's what's happening, hour by hour, and what to do about it.

100x how much your inflammation signal spikes during a 100-miler vs. resting
2-6 days when muscle damage markers peak after the race, not during it
3-4 wks how long full recovery takes for most systems

What Happens Inside Your Body After an Ultramarathon?

IL-6 is a chemical signal your muscles send when they get damaged. It shoots up to 100 times your normal level during the race. Think of it as the alarm going off. It starts dropping after you finish, but the damage it triggered keeps unfolding for days.

CRP is how your liver responds to that alarm, about 12 hours later. It peaks 1 to 3 days after the race. Normal CRP is below 1 mg/L. After a 100-mile race, values of 10 to 40 mg/L are typical, and it is usually back near normal within a few days.1 The morning after your finish, a blood test would look like you're fighting a moderate infection.

Creatine kinase (CK) leaks out of torn muscle fibers. It doesn't peak during the race. It peaks a few days after. Downhill running is hard on muscles, so the more downhill you ran, the higher it tends to go.2

How Long Does It Take to Recover After a 100-Mile Race?

Window What's Happening What to Do
Hours 0-6 Inflammation at its peak. Body temp still high. Fuel and salt depleted. Immune system suppressed. Get warm. Drink broth or an electrolyte drink. Eat whatever you can stomach. Skip the ibuprofen. Sleep if you can.
Hours 6-24 Inflammation starting to drop. CRP is rising. Muscle damage still building. Your immune system is still suppressed.3 Keep eating. Protein at every meal. Wash your hands. Avoid crowds. Walk around, don't just sit still.
Hours 24-72 CRP and muscle damage near their peak. Soreness is worst around 48 hours. Low energy, bad mood, and brain fog are normal. Your body is doing this, not your head. Keep walking. Sleep as much as you can. Protein at every meal. Cold water on sore muscles can help a little.
Days 3-7 Inflammation slowly coming down. Gut bacteria are disrupted.4 Post-race low mood is common. Appetite and sleep still off. Still no running. Walking is fine. Eat real food. Yogurt and fermented foods can help your gut bounce back.
Days 7-14 Blood markers mostly returning to normal. Muscles healing. Tendons and connective tissue are still behind. Easy jogging is okay after day 10 if it feels right. Your heart rate will be higher than usual for the same effort. That's normal. Don't push pace.
Weeks 2-4 Most markers back to normal. Muscles feel okay. Tendons still finishing up. Ease back into real training. No hard workouts until week four. If you're over 40, add an extra week to each phase.

Should You Take Ibuprofen?

A lot of runners do. The problem: the inflammation causing your soreness is also what tells your muscles to rebuild. Ibuprofen can dull both. Short-term studies show drugs like ibuprofen can blunt your muscles' rebuilding signal right after hard exercise. Longer studies have not shown they hurt training gains.5

If the pain is bad enough to keep you awake, that's a different situation. But there's little reason to take it around the clock for days. It may mask pain you should listen to.

Better option: Acetaminophen (Tylenol) handles pain without blocking the repair process. It's a better fit for post-race recovery. Don't exceed 4g per day, and check other products you're taking for hidden acetaminophen.

Watch for this in the first 48 hours: Dark brown or tea-colored urine, severe muscle swelling, or pain that feels worse than expected. These can be signs of serious muscle breakdown and need medical attention right away.

What Actually Speeds Up Recovery After an Ultra?

Sleep more than you think you need. Aim for 9 to 10 hours per night for at least four nights after the race. A 2026 study put motion sensors on 18 runners after a 64 km mountain race. Their sleep was broken up for up to four nights. They woke up more often and spent more time awake at night.7 Most runners said their sleep was only a little worse. How you think you slept does not tell the full story. Your body does most of its repair during deep sleep, and it is the most effective recovery tool you have.6

Eat protein at every meal. About 1.6 to 2.1 grams per kilogram of body weight, spread across the day.8 Dairy sources like cottage cheese, Greek yogurt, and whey work especially well.

Walk every day. Moving keeps blood flowing to damaged tissue without adding stress. Easy walking beats sitting still every time.

When Can You Run Again?

Most runners can handle easy jogging around day 10 to 14. Don't go by soreness alone. Your tendons and joints heal slower than your muscles, and they don't always warn you before they give out.

A safe plan: week one is walking only, week two is short easy runs every other day, week three is back to normal easy miles, and no hard workouts until week four.

Sources
  1. Waśkiewicz Z, et al. "Inflammatory Response to Ultramarathon Running: A Review of IL-6, CRP, and TNF-α." International Journal of Molecular Sciences. 2025;26(13):6317. doi:10.3390/ijms26136317
  2. Radišić Biljak V, Lazić A, Nikler A, Pekas D, Saračević A, Trajković N. "Post-exercise creatine kinase variability: a literature review." Biochemia Medica. 2025;35(2):020502. doi:10.11613/BM.2025.020502
  3. Gleeson M. "Immune function in sport and exercise." Journal of Applied Physiology. 2007;103(2):693-699. doi:10.1152/japplphysiol.00008.2007
  4. Sato M, Suzuki Y. "Alterations in intestinal microbiota in ultramarathon runners." Scientific Reports. 2022;12:6984. doi:10.1038/s41598-022-10791-y
  5. Trappe TA, Liu SZ. "Effects of prostaglandins and COX-inhibiting drugs on skeletal muscle adaptations to exercise." Journal of Applied Physiology. 2013;115(6):909-919. doi:10.1152/japplphysiol.00061.2013
  6. Watson AM. "Sleep and Athletic Performance." Current Sports Medicine Reports. 2017;16(6):413-418. doi:10.1249/JSR.0000000000000418
  7. Fachan F, Vilcourt F, Lemarchand B, Chouchou F. "Sleep disturbances after an ultra-trail endurance race: a field study." Sleep Medicine: X. 2026;12:100197. doi:10.1016/j.sleepx.2026.100197
  8. Tiller NB, Roberts JD, Beasley L, et al. "International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing." J Int Soc Sports Nutr. 2019;16(1):50. doi:10.1186/s12970-019-0312-9

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