Running a marathon certainly impacts how your body feels. But what actually happens internally? During a race, the body goes into overdrive, uses up energy stores, breaks down muscle, and loses fluid and electrolytes. And afterward, the body needs to recover from that damage. Measuring blood biomarkers post-race can provide you with real data on your recovery status and explanations for how you feel physically after an intense event. This article outlines what to expect from your body and your blood biomarkers after running a marathon and evidence-based recovery strategies that’ll help you feel strong and recovered by your next starting line.
What to expect from biomarkers post-marathon
Running a marathon is undoubtedly strenuous on the body. And your biomarkers will likely sharply fluctuate in response. Here’s the science behind five biomarkers impacted by a marathon.
HsCRP and inflammation stay high for multiple days after a marathon
The biomarker hsCRP measures the body’s general inflammation levels and provides unique insight into athletic performance and recovery. It’s no secret that running a marathon can leave your joints and muscles inflamed. Continuous strenuous exercise can increase inflammation and cause markers like hsCRP to stay elevated. And while some acute inflammation is necessary for the body to grow and repair muscles, uncontrolled inflammation can halt muscle gains. 
Levels of hsCRP typically peak within 24 hours of intense exercise and can stay elevated for up to seven days. One study investigated the impact of marathon running on blood biomarkers in 86 runners. Researchers found that eight days post-marathon, hsCRP levels were still higher than baseline levels. 
Figure 1: Results of the Wilcoxon test. Evolution of the CRP. p<0.005.
Taken from: Bernat-Adell MD et al. J Strength Cond Res., 2021 
Testosterone levels can drop after a marathon
Testosterone is a crucial hormone for male and female athletes alike. Testosterone is anabolic, meaning it triggers processes that build tissue and help it recover. Testosterone impacts marathon performance; low levels of free testosterone are associated with improper recovery, impaired fitness gains, and increased risk of injury. This hormone also stimulates red blood cell production, which is important for transporting oxygen from the lungs to muscle tissue, especially essential during a marathon. 
Markers like testosterone typically detail a longer-term view into how an athlete is handling a training cycle. If the training intensity is too high, race day can increase sex hormone-binding globulin (SHBG) levels—which almost always coincide with below-optimal levels of free testosterone.  Going into a marathon with increased SHBG levels and decreased free testosterone can slow down post-marathon recovery.
Studies show that training can increase testosterone levels, but testosterone levels may plummet after longer distances like a marathon.  Avid marathoner and sales manager at InsideTracker, Jonathan Levitt, comments on the change in testosterone levels he experienced before and after running a particularly difficult marathon. His testosterone levels didn't just drop—they also took a significantly longer time to recover than normal. And his body felt it too. “I was overtrained coming into that marathon, and I did everything wrong leading up to it. I ended up not racing well, and it was all connected.” After seeing the data on his testosterone levels, he took 21 days off of running.
Cortisol can increase from the physical stress of running a marathon
Cortisol, the “stress hormone,” increases in response to both emotional stress and physical stress like a marathon. Cortisol is important for short-term energy production to meet the immediate energy demands a marathon requires. However, prolonged high cortisol levels signal the body to diversify its fueling sources—including breaking down muscle for energy. When cortisol and stress levels are elevated, performance and recovery can decline. 
Post-marathon cortisol levels increase proportionally to testosterone’s decrease. High cortisol combined with low testosterone is characteristic of inadequate recovery. In fact, changes in cortisol levels typically correspond to similar changes in testosterone post-marathon. 
Creatine kinase peaks 24 hours after strenuous exercise and can stay elevated
Creatine kinase is an enzyme primarily stored in muscle tissue. During intense training, creatine kinase leaks into the bloodstream, rising about 12-48 hours post-workout.  Moderate levels of creatine kinase in the blood are normal. However, high creatine kinase levels can indicate muscle damage. Therefore, creatine kinase levels can show the extent to which your muscles are over-exerted. Studies show that creatine kinase levels peak about 24 hours post intense exercise. And though creatine kinase levels tend to decrease after that 24-hour mark, they can remain elevated for six days post-race.  Interestingly, the rate of creatine kinase recovery is an indicator of how the body handled its training. Creatine kinase levels tend to recover faster after a marathon in trained athletes but can recover more slowly in overtrained individuals.
Figure 2: Results of the Wilcoxon test. Evolution of CK. p<0.005.
Taken from: Bernat-Adell MD et al. J Strength Cond Res., 2021 
Biomarkers to optimize before race day
There are other biomarkers that, when left unoptimized, have an impact on marathon performance. For example, ferritin (the storage form of iron), vitamin D, and vitamin B12 are three biomarkers to be proactive about prior to race day. Stevie Smith, Ironman athlete and sports dietitian, talked to InsideTracker about the most common biomarker she works on with clients leading up to a marathon. “Ferritin is often a struggle for female athletes (including myself!), but it is so important for marathon performance.” Read more about how these three biomarkers impact athletic performance here.
What to do within 24 hours of a marathon to properly recover
Running a marathon is a huge physical feat, and it can do a lot of immediate damage to the body. Proper rest and recovery from a marathon are essential to ensure longevity in the sport. And the first 24 to 48 hours after a race are the most important. Here’s what to do during this critical recovery window.
Hydrate and replace electrolytes
Your absolute first priority after crossing that finish line is to hydrate and get some electrolytes. “You should be getting 24 ounces of fluid per pound of weight lost,” says Stevie, “and there’s usually about 1 gram of sodium in every liter of sweat.” So say you lose 2 pounds of body weight after a marathon, you would need to take in about 47 ounces of fluid (about 1.4 L) and about 1.4 grams of sodium.
Don’t feel the need to chug this all at once, but rehydrating with fluids and electrolytes is an immediate priority post-marathon. 
Eat a balanced recovery meal
What you eat is just as crucial as what you drink. And electrolytes like sodium can also come from food. The ideal post-marathon meal contains a balance of carbohydrates, protein, fat, and micronutrients. 
“One of my favorite post-marathon meals is a turkey sandwich with veggies and a side of fruit and chips (salt + carbs + protein!). This meal is usually an hour or so post-race, so I make sure I have a snack like chocolate milk and a banana right after the race,” says Stevie. Protein is needed to prevent excess muscle breakdown and carbohydrates are needed to replenish energy stores. An ideal ratio of these two macronutrients is three grams of carbohydrates to every gram of protein consumed.
If you’re unable to eat a full meal within an hour after the race, opt for a snack first to tie you over.
Keep moving, but slowly
Runners and running coaches also recommend light, easy movement post-marathon. Jonathan says that he likes to walk for 30 minutes after a race as a form of active recovery. “This will allow your heart rate time to slowly lower and keep blood flow strong to the exhausted muscles—helping clear lactic acid and initiating the recovery process,” says Stevie. 
What not to do post marathon—habits that prolong recovery
Certain choices you make post-marathon may actually hinder recovery and delay the healing process.
Don’t drink too much alcohol
Finishing a marathon is a feat to celebrate! And drinking alcoholic beverages is frequently a part of those festivities. “Alcohol can negatively affect muscle protein synthesis, which interferes with repairing the damaged muscles from the marathon,” says Stevie. But the choice to consume alcohol or not post-marathon is highly personal.
Stevie notes that, “if someone is racing and then looking to turn back into a heavy training cycle for another race later in the season, it’s probably not the best idea to imbibe post-race. If an athlete does choose to enjoy a few adult beverages, I recommend they do so in moderation while prioritizing eating nutrient-dense foods and not neglecting hydration.”
Jonathan also says he often sees runners switch to beer too fast after a race without drinking enough water. And beer and other alcoholic beverages don’t count towards those post-marathon rehydration goals. Alcohol acts as a diuretic, further ridding the body of salt and water. When already dehydrated from sweat loss post-marathon, alcohol intake can make matters worse.  Therefore, be sure to replenish with fluid and electrolytes prior to a celebratory beverage.
Don’t restrict or limit food intake
In the hours and days following a marathon, runners should aim to eat consistent meals and snacks throughout the day to get enough carbohydrates, fat, protein, and color. Evidence suggests that beneficial plant compounds called polyphenols (like those found in green tea) may be protective of exercise-related muscle damage and the internal stress that causes in the body.
When counseling her clients, Stevie often encourages them to lean into their hunger cues. “It’s normal for appetite to be suppressed for a day or two after a marathon. So when the hunger hits, it’s important to listen to your body—if a burger sounds good, have a burger! Just don’t neglect nutrient-dense foods." 
Don’t do too much too soon
Take some time off from intense exercise after a marathon. Your body needs time to rest and recover. Marathons can throw biomarkers like CK, testosterone, cortisol, and hsCRP completely out of whack, and the best way to get them back to optimized is through resting your stressed body—not by piling on more stress. Lower intensity activities like walking, yoga, or stretching offer the benefits of movement while allowing those biomarkers to recalibrate. After proper rest and recovery, training volume can be picked up again.
Should you run the day after a marathon?
The short answer here is, probably not. And this is a great example of doing too much too soon.
“Running the day after completing a marathon is not recommended. How long that rest period lasts should be is based on a number of factors. This includes an athlete's training status, goals, and mental and physical health. For the most part, I’d recommend taking at least a whole week off from running (if not more),” says Stevie.
Some people may be ready to run again within a week, whereas others want to take more time off. And some runners may choose to run races back-to-back, or within the same week. It’s best to talk with a running coach to determine your ideal race and training schedule. But running too hard too soon after a marathon may increase the risk of injuries. 
Why can’t you sleep after a marathon?
“Sleep can be challenging after a hard physical effort for a number of reasons. A hormonal response to exercise, including cortisol and norepinephrine (which makes your heart beat faster), dehydration, elevated core body temperature, and high caffeine intake during races can all negatively impact sleep,” says Stevie. High heart rates keep you alert, which is not ideal for sleep. Body temperature begins to drop around bedtime, so a high internal temperature can delay the signal that it’s time to wind down and go to sleep.
“I couldn’t sleep after a marathon because my quads were vibrating, and I took in 8-10 caffeinated gels during the race,” says Jonathan. For reference, that’s about 400-500 mg of caffeine—equivalent to around 5 cups of coffee. He also notes that “a lot of people may have 10 beers or so post-race. That, mixed with caffeine, can definitely have an impact on sleep.”
A post-race high is also common among runners. This high can be emotionally and physically driven. You’re proud of yourself for finishing a marathon, and your stress hormones cortisol, norepinephrine, and adrenaline are likely still elevated. A 2020 study shows that norepinephrine and adrenaline return to near-normal by a week after a marathon. 
Concerned about your recovery? When should you contact a doctor or other health professional?
Different bodies recover at different speeds. However, “after proper rest, the biomarkers related to muscle health, immune health, and stress that spiked because of the marathon should start to drop back to normal levels,” says Stevie. “If these biomarkers remain extremely elevated a few weeks post-race, I’d recommend evaluating your rest and recovery and contacting a professional.”
A blood test is needed to measure these biomarkers. If you are running consecutive races, it may be beneficial to get a blood test between races to get an objective view of how your body’s actually recovering and whether you recovered to the extent needed for your next race.
- Biomarkers like hsCRP, creatine kinase, cortisol, and testosterone are altered in the 24 hours following a marathon, and their recovery back to baseline is indicative of training.
- Ferritin, vitamin D, and vitamin B12 are three biomarkers to be proactive about optimizing prior to race day.
- After crossing the finish line, it’s important to keep moving for a bit to get your heart rate back down, rehydrate with fluids and electrolytes, and eat a balanced recovery meal that consists of carbohydrates, protein, and some color.
- Common post-marathon mistakes to avoid include drinking too much alcohol and restricting food intake, which can hinder recovery.
- If you’re at all concerned about how well your body is recovering, consider getting a blood test with InsideTracker to measure recovery related biomarkers or contacting a health professional.
- If you experienced an injury during a marathon or from activity following a marathon, seek medical attention.
InsideTracker is an incredibly useful resource to not only measure your blood biomarkers, but to learn what can help improve them. Whether you’re in the middle of your training season or working on post-marathon recovery, InsideTracker can help you reach your unique goals. The Ultimate Plan is InsideTracker's most comprehensive plan and includes
- Testosterone (men and women)
- Vitamin D
- Vitamin B12.
You can then select a goal, like improve Endurance, and InsideTracker will give you personalized food, supplement, and lifestyle recommendations to help you reach that goal. And if you have a Garmin smartwatch or Fitbit, the devices can sync with the InsideTracker app and pull data on your heart rate and sleep. Learn more about the plan here.
Jonathan is a marathoner who dabbles in longer trail adventures. While not helping future InsideTracker customers learn about their journey to improved health and performance, he's running, biking, or hosting his podcast, For The Long Run!
Stevie Lyn Smith, MS, RDN, CSSD, CDN
Stevie Lyn is a Content Strategist and Team Nutritionist at InsideTracker. As a Registered Dietitian and Ironman triathlete, she enjoys combining her passions to help educate others on how to fuel for overall health and performance. When she’s not swimming, biking, or running with her dog, you’ll find her in the kitchen working on a new recipe to improve her biomarkers.