Feeling sick after a workout can be discouraging, but it’s not uncommon. Flu-like symptoms after exercise can be due to a number of factors such as dehydration, low blood sugar, or overexertion.
Dehydration
Sweaty workouts can cause you to lose fluids and electrolytes. The Cleveland Clinic notes that not replacing them can lead to symptoms of dehydration, like fatigue, muscle pain, nausea and vomiting.
Drinking plenty of fluids and making sure you’re well hydrated before strenuous exercise can help prevent symptoms of dehydration, according to a 2023 review in Sports medicine.
Low blood sugar
According to a study published in Sporty In 2019, not eating enough before exercising can lead to hypoglycemia (hypoglycemia). Low blood sugar can cause flu-like symptoms, like nausea, clammyness, or dizziness, notes the American Diabetes Association.
Eating a light snack before working out can help prevent symptoms of hypoglycemia.
Exercising after eating
Eating a large or high-fat or fiber meal before exercising may increase abdominal discomfort, according to a 2025 review in World Journal of Gastroenterology. This can cause undigested food to sit in your stomach longer, leading to feelings of nausea. Researchers note that this is especially true during high-intensity or endurance exercise.
Changing your meal schedule or eating lighter meals before exercising can help prevent unpleasant gastrointestinal symptoms.
Overexercise
Constantly pushing your body too hard during workouts or exercising too often can cause flu-like symptoms, like persistent muscle aches and fatigue, notes the Cleveland Clinic. It can also reduce your body’s ability to fight colds and infections.
According to a review published in 2023 in DieteticProlonged, strenuous exercise can also lead to exercise-induced gastrointestinal syndrome (EIGS), which often causes nausea.
How to Prevent Flu Symptoms After Exercise
If you experience flu-like symptoms after a workout, here are some steps you can take to prevent them:
- Make sure to stay hydrated, especially when you exercise.
- Try spacing out higher-intensity workouts to give your body time to recover.
- Eat a high-carb snack to energize your body before hitting the gym.
- Avoid large meals before exercising.
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