Why Do I Feel Sick After a Marathon? 3 Common Reasons

3 Reasons You May Feel Sick After a Marathon

Completing a marathon is a monumental achievement, but the days that follow aren’t always filled with celebratory energy. Many runners experience a range of unpleasant symptoms – from gastrointestinal distress to feelings of sadness – that can linger for days after crossing the finish line. This post-marathon malaise is often referred to as the “marathon flu,” but it’s more complex than simply pushing your body to its limits.

Gastrointestinal Issues

Upset stomach and the urgent need for bathroom breaks are common complaints among marathon runners, both during and immediately after the race. The underlying cause often relates to the body’s stress response during intense physical exertion.

“When you’re running the marathon, your [physical] stress levels go high,” explains New Jersey-based running coach Erica Coviello, a Road Runners Club of America (RRCA)–certified running coach and an American Council on Exercise (ACE)–certified personal trainer. “It puts you into that flight-or-fight response mode, and in doing that, your blood flow changes and your body is like, ‘What the heck is going on?’ It reroutes the blood to essential organs and away from your gut.”

This diversion of blood flow away from the digestive system can lead to nausea and other gastrointestinal issues. According to Coviello, this response can persist for several days post-marathon.

‘Post-Marathon Depression’

Beyond the physical toll, many runners experience a sense of loss and sadness following a marathon, sometimes referred to as the “marathon blues.” This isn’t necessarily a clinical depression, but a common emotional response to the culmination of months of dedicated training.

“You spend so much time and so much of your schedule regimented toward that one event,” Coviello says. “Whether you completely crush your goals or you have completely failed, that’s the climax. Then you’ve got a day or two of celebration, and then many people wonder what they’re supposed to do now.”

The sudden absence of a central focus can create a void, and for individuals already managing mental health conditions like depression or anxiety, these feelings can be amplified. Coviello emphasizes that this emotional response is a “real thing” that requires attention and care during recovery.

Underlying Infection

Sometimes, what feels like the “marathon flu” is, in fact, a genuine illness. The extreme physical stress of a marathon can temporarily suppress the immune system, making runners more susceptible to infections that may have been brewing or contracted during the event itself.

The combination of exhaustion, immune system compromise, and close proximity to large crowds at races can create an environment conducive to catching a cold, the flu, or other viral infections. Post-marathon symptoms could represent the onset of a true illness requiring rest and appropriate medical care.

Understanding the Runner’s Flu

The experience of feeling unwell after a marathon is multifaceted, involving physiological and psychological factors. It’s important to recognize that the symptoms are often a normal response to the extreme demands placed on the body. However, distinguishing between typical post-race malaise and a developing illness is crucial.

Dehydration, as noted by experts, also plays a significant role in post-marathon nausea. Sweat loss throughout the race depletes fluids and electrolytes essential for proper bodily function. Restoring these lost fluids and electrolytes is a key component of recovery.

A study published in 2023 in Frontiers of Physiology examined 40 runners who participated in the 2019 Boston Marathon. Researchers found that gastrointestinal symptoms and intestinal cell damage were most pronounced immediately after the race, with nausea, stomach pain, and belching being the most frequently reported issues. The study suggested that exercise intensity, sleep, fuel, and hydration all contribute to the severity and incidence of GI distress.

What to Do If You Feel Sick

While there’s no quick fix for the “marathon flu,” prioritizing rest, hydration, and nutrition is essential. Listen to your body and allow adequate time for recovery. If symptoms are severe or persist beyond a few days, or if you develop a fever, chest pain, or other concerning signs, seek medical attention. It’s always best to err on the side of caution and rule out any underlying medical conditions.