Why Are You Feeling Flu-Like Symptoms After Exercise?

People often talk about how energized they feel after exercising, but that’s not everyone’s experience. Sometimes, a workout can leave you feeling off – like you’re coming down with the flu. So many people deal with exercise-induced flu-like symptoms, some of which can be downright debilitating.

But you don’t have to simply accept that exercise and flu symptoms go together. This article will help you pinpoint why you’re feeling flu-like symptoms after exercise. Then, we’ll touch on the primary causes of flu-like symptoms post-exercise, prevention and recovery tips, and answer frequently asked questions about this topic.

A Note on Post-Exertional Malaise (PEM)

While it may be common for some to experience flu-like symptoms after exercise, other people experience these symptoms delayed and more severely in a condition called Post-Exertional Malaise (PEM). This is NOT your typical fatigue after exercising and is more so common with those who have, or have had, Chronic Fatigue Syndrome (CFS) and Long COVID.

For those who have PEM, physical and mental exertion can cause:

• Extreme fatigue, worsening after 12-48 hours post activity;
• Headaches, nausea, muscle pain, or flu-like symptoms;
• Brain fog;
• Difficulty concentrating
• A crash that can last days or worse, weeks.

If you have, or have had, CFS or Long COVID and/or experience these symptoms, pushing through can cause harm. Please check with your healthcare provider for ways to safely begin moving your body.

Common Symptoms Experienced Post-Exercise

Post-exercise symptoms range from muscle aches and fatigue to nausea and dizziness, and more. Below are a few of the most common symptoms people deal with after exercising.

Muscle Aches and Fatigue

Muscle aches and fatigue are two post exercise symptoms mimicking flu symptoms that health professionals regularly see with exercise. They’re believed to be caused by repetitive usage of muscles; the muscles temporarily weaken. And this is totally normal.

You may feel any of the following when dealing with this post-exercise symptom:

• Localized pain;

• Soreness;

• Shaking or twitching;

• Weakened grip;

• Cramps in the muscles that were used during exercise.

Note: Muscle aches and fatigue can also be associated with numerous ailments unrelated to exercise. Anemia, anxiety, depression, fibromyalgia, lack of exercise, and mineral deficiency are a few.

Nausea and Dizziness

After exercising, you may also feel sick or off-balance. Dizziness and nausea reminiscent of the common cold, flu, or stomach virus are typical after a workout, especially with strenuous exercise or overexertion.

Severe symptoms like these may even lead people to abandon their fitness goals.

Headache and Chills

Headaches (also called exertion headaches) might set in during or after you’re done exercising. People tend to experience them for just a few minutes, but they can hang around for hours occasionally.

You may also notice temporary full-body chills or a general cold feeling.

Primary Causes of Flu-Like Symptoms After Exercise

Have you been dealing with the flu-like symptoms outlined above? It’s time to get to the bottom of things by breaking down the factors and causes of these exercise-induced symptoms.

Dehydration and Electrolyte Loss

78% of your body is made up of water, an essential substance for countless body processes, like body temperature regulation, bone cushioning, digestion, and more.

So, when you’re dehydrated from exercise-related fluid loss and lose too many electrolytes, you could suffer from all of the flu-like symptoms above.

Hormonal and Stress Responses

Working out elicits both a hormonal and stress response; the intensity of the response varies from individual to individual.

Studies have shown that anabolic hormones like testosterone and human growth hormone (GH) become elevated during 15-30 minutes of post-resistance exercise. Cortisol (the main stress hormone) also rises and can cause headaches. Growth hormone, which is essential for muscle repair and tissue growth, causes nausea.

Lactic Acid Buildup

As you work your muscles and feel the burn, lactic acid (cell fuel) increases.

Some experts believe that once it has built up beyond a certain point, and you develop lactic acidosis, you’ll start to feel muscle soreness and fatigue. That’s your body begging you to stop where you’re at and rest.

You may also feel exercise-induced nausea, whole-body weakness, and other flu-like symptoms.

Reduced Immune Function

Some experts believe that after a bout of extreme exercise out of nowhere, or several bouts with inadequate rest in between, your immune function may dip.

This leaves you vulnerable to one or more infectious diseases in circulation at any given time. Though, in the long term, moderate exercise is beneficial for your immune system.

Lifestyle and Dietary Contributors

What you eat has a monumental effect on how you feel during and post-workout.

If you eat greasy fried food before running on a treadmill, you may feel sick afterward. Also, if you live a very sedentary lifestyle where you spend most of your time seated, once you engage in higher levels of activity, your body may revolt, making you feel nauseous and extremely fatigued.

Blood Sugar Levels and Nutrition

Both aerobic and cardiovascular exercise affect your blood sugar levels. As you get moving, the reserve sugars that are stored in your liver and muscles are depleted. Sugar is taken from your blood to make up for this.

While you’re in a low blood sugar state (which lasts for several hours), you could experience flu-like symptoms like dizziness, nausea, shaking, and more.

Timing of Meals and Hydration

Having a large meal or a giant bottle of water right before exercising ratchets up your risk for digestive problems.

Experts recommend that you plan your workouts 1 to 2 hours after a meal and half an hour after having a snack. The key is to give your stomach a little time to digest before exercising.

Chronic Conditions (CFS, Fibromyalgia)

Certain chronic conditions, like chronic fatigue syndrome (CFS), can be exacerbated by exercise. If you have this condition, strenuous exercise can make you feel like you’re battling the flu.

Fibromyalgia can have a similar effect on your workout, worsening the symptoms associated with the condition, especially if the workout is moderate to vigorous in intensity.

Overexertion and Physical Exhaustion

Going overboard during a workout can lead to overexertion and physical exhaustion, both of which can make you feel like you have the flu.

Some of the symptoms include dehydration, muscle pain, and even difficulty breathing, which often mirror cold and flu symptoms.

Inflammatory Response and Muscle Micro-Tears

The act of exercising can bring on an inflammatory response, which can make you more susceptible to minor illnesses.

Also, physical activity makes tiny micro-tears in the muscles targeted in your workout. These tears eventually heal and become stronger, but while the body repairs itself, muscle weakness and delayed onset muscle soreness can occur.

Practical Prevention and Recovery Tips

If you’re feeling flu-like symptoms after exercise, we’ll bet you want to figure out how to minimize them. This section will help you find relief.

Balanced Hydration

You’re going to lose fluid during each workout, so how much water you drink matters.

About two hours before starting any workout, drink enough fluids – about 20 ounces of water. Then, for every 15 to 20 minutes, drink between 4 to 8 ounces more. Stay closer to four ounces if you’re not working up a sweat or are working out in a cooler area.

Keeping properly hydrated wards off dehydration and electrolyte imbalances. It also reduces your chance of overheating and aids in muscle recovery post-workout.

Gradual Intensity Increases

If you’re new to exercising or aren’t in very good shape, don’t start off with intense exercise.

Instead, start off with lighter workouts and steadily increase the difficulty. You might begin with a stroll through the neighborhood or walking on a low-impact treadmill before trying high-energy cardio or HIIT.

Doing so will reduce muscle soreness, weakness, and other flu symptoms related to overly vigorous exercise.

Proper Nutrition

Poor nutrition increases your chance of developing flu-like symptoms after a workout. To combat that, fuel your body with a diet rich in complex carbohydrates (like whole grains), and be sure to get your protein in both meals and snacks. Never forget your healthy fats (olives, nuts, seeds, etc.).

You’ll also need ample veggies and fruits on a regular basis. Before starting your workout, have a pre-workout snack, like nut butter or bananas. And, don’t skip breakfast!

Incorporate Rest Days

If you’re going to avoid exercise-induced flu-like symptoms, you’ll need to rest and recover after exercising. Doing so will ease your body’s rejuvenation process and dull some of the symptoms that come up for you.

Most people benefit from active resting, 1-2 days per week. And when you do a very high-intensity exercise, you’ll need at least 24 hours of active recovery before your next workout. We also recommend getting enough sleep; 7 to 9 hours per day is ideal for adults.

Learn about how to relieve muscle pain after exercise in this article.

When to Seek Medical Advice

If you’re worried about your health or are still experiencing bothersome flu-like symptoms after implementing the above tips, we recommend speaking to a healthcare professional for medical advice.

The doctor will examine you and talk to you about your exercise habits, how you prepare for workouts, the symptoms you’re experiencing, etc. They can then answer your questions, share tailored tips, and draft a treatment plan to get you feeling better fast.

Advice from a personal trainer can also be helpful for non-life-threatening concerns.

One of the most powerful tools for recovery and reducing post-exercise symptoms is quality sleep, which plays a key role in muscle repair, immune support, and overall energy restoration.

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Frequently Asked Questions

What are the signs of overexertion?

Remember that while we’re here to guide and support you, always check with your healthcare provider for any concerns – your health comes first.

With that said, here are some common signs to watch for when it comes to overexertion:

• More colds/sicknesses than what’s normal for you;
• Pain;
• Injuries from overuse;
• Marked tiredness;
• Trouble breathing while doing a given exercise.

If you push so hard that it feels like you can barely walk, you’ve likely overexerted yourself – or it could be a sign of a more serious condition like rhabdomyolysis. This is a rare but dangerous medical condition that can happen after extreme or prolonged exercise and requires immediate medical attention.

Can you feel like you have the flu but no fever?

Yes, you can feel like you have the flu without a fever.

This might happen during or after exercise, and for many other reasons:

• Bacterial or viral infections (respiratory syncytial virus, COVID, common cold, influenza);
• Prescription or medical treatment side effects;
• Infections spread by animals.

Can sore muscles make you feel sick?

Yes, sore muscles can definitely make you feel like you’re ill, even if you’re not. This is because muscle soreness is a typical symptom of cold and flu viruses, as well as other illnesses.

Sources

Muscle Fatigue: Causes, Symptoms, and Treatment

Exertion Headaches

Dehydration

Electrolyte Imbalance

Hormonal Responses and adaptations

Lactic Acidosis and Exercise

Flu Symptoms After Exercise

Can I Exercise With a Cold or the Flu?

Does Exercise Boost the Immune System?

Diabetes and Exercise

Low Blood Sugar

How Long Should You Wait to Exercise After Eating?

Exercise Therapy After Fibromyalgia

Tips to Maximize Muscle Recovery

A Freezing New Way to Recover From a Workout