Having an upset stomach during or after exercise may have a variety of causes including lactic acidosis, low blood sugar, dehydration or eating too much before your workout. Generally, nausea will resolve on its own and you can prevent it in the future with adjustments to your routine.
Exercise can trigger an upset stomach and nausea in certain circumstances, such as when you don't properly fuel your body or when your body overheats. It may also be a result of lactic acidosis.
Intense Exercise and Lactic Acidosis
Lactic acid was once a popular scapegoat blamed for causing muscle soreness after your workout. Research has revealed that lactic acid, or lactate, actually functions as an energy reserve that can be used for both aerobic and anaerobic respiration, advises the National Academy of Sports Medicine. It is produced when cells do not have enough oxygen and resort to breaking down glycogen or glucose for energy.
During intense exercise, lactic acid builds up in your system and creates acidity in your muscles. When it reaches the lactic threshold, the maximum amount that can be held in the cells, the weak acid is removed from the muscle cells and taken into the bloodstream. Sodium and potassium in your blood binds with the lactate, which helps to keep your blood's pH stable. These compounds are then returned to cells as needed for energy or filtered out in the liver.
In rare cases, during extremely intense exercise, your blood cannot keep up with the production of lactate, resulting in acidosis. Symptoms include nausea, vomiting and weakness. Generally, the built-up lactic acid dissipates within an hour after you finish your workout.
If there is another underlying cause for the acidosis, additional treatment may be necessary. Some other conditions that may cause lactic acidosis include kidney failure, cancer and alcoholism, notes the U.S. National Library of Medicine.
Taking a small amount of sodium bicarbonate, or baking soda, before your workout can help reduce metabolic acidosis caused by intense exercise, claims the National Academy of Sports Medicine. Use caution with this method as the baking soda itself can cause nausea and diarrhea.
Read more: Baking Soda for Sore Muscles
Stay Hydrated and Eat Properly
Proper nutrition and hydration are critical to getting the most out of your workouts. Dehydration can cause a number of symptoms, including nausea, dizziness, a dry or sticky mouth and dark-colored urine, notes the University of Michigan Health System. When you sweat during a workout, you lose water and electrolytes. If you don't drink enough water before and during your workout, you may quickly become dehydrated, especially during warm weather.
Dehydration can be life-threatening in extreme cases, so don't ignore the symptoms and attempt to power through your workout. If you are dehydrated, stop your workout and drink plenty of fluids to rehydrate. Focus on water and sports drinks and avoid caffeinated beverages.
Drinking plenty of water before your workout can help you avoid dehydration, but be careful not to chug too much right before your workout. If you choose other drinks such as coffee or juice, be aware that they can also cause an upset stomach for some people, advises the National Academy of Sports Medicine.
It is also very important to make sure that you eat before your workout so that your body has fuel for the exercise, notes Columbia University. If you don't eat, you may experience low blood sugar during your workout, advises the University of Rochester Medical Center. This may cause:
- Upset stomach
- Rapid heartbeat
- Blurred vision
- Tingling around the mouth
Stop and eat a snack with carbohydrates in it to replenish your body. Pay attention to what and when you eat before workouts so that you can find out what kind of foods work for you to get the best workout possible.
Your pre-workout snack should contain plenty of carbs and a small amount of protein to give your body the energy you need for your workout, notes the American Council on Exercise. Avoid high amounts of fat and fiber as they may cause an upset stomach. Here are a few ideas you can try before your next workout:
- Cheese and crackers
- Turkey sandwich
- Peanut butter and banana
Avoid Heat Exhaustion From Exercise
Heat exhaustion is a common concern for athletes. When you exercise, your body is generating heat, raising your blood temperature. Sweating is your body's way of cooling its core temperature, notes Johns Hopkins Medicine. Moving more blood to the surface of your skin further allows heat to escape, keeping your body cool.
If your body cannot keep cool, you develop heat exhaustion. At this point, your temperature will have risen to 101 to 104 degrees Fahrenheit. In addition to an upset stomach, symptoms include:
- Diarrhea and vomiting
- Dizziness and fainting
- Rapid heartbeat and breathing rate
- Excessive sweating
- Muscle cramps
- Weakness and poor coordination
- Mild confusion
There are several factors that increase your risk of developing exercise-related heat exhaustion. Some of these include:
- Exercising in hot temperatures
- Being overweight
- Drinking alcohol before exercising
- Certain medications including antihistamines and stimulants
If you have heat exhaustion, stop your workout immediately and rest. Move to a cooler area and get out of the sun if you are outdoors. Take off any extra clothing layers and lie with your legs at a higher level than your head to make sure enough blood is getting to your heart. Drink a sports drink or water and do what you can to cool off. This may include sitting in front of a fan, spraying yourself with cool water or soaking in cool water.
If your symptoms do not improve within an hour or two hours, seek medical attention. If heat exhaustion is not treated it can progress into heatstroke. Heatstroke is very serious and can cause seizures, heart failure, liver or kidney damage, delirium, coma and even death.
Reduce risk of heat exhaustion by avoiding exercise in extremely hot temperatures, especially if you aren't used to the heat. If you exercise outdoors, schedule your workouts for morning or evening when the temperatures are cooler. Wear lightweight and loose-fitting clothing and a hat and sunscreen if you are outdoors. Stay hydrated and take plenty of breaks.
- U.S. National Library of Medicine: "Lactic acidosis"
- National Academy of Sports Medicine: "The Lactic Acid Lowdown: Clarifying Common Misconceptions"
- University of Michigan Health System: "Preventing Dehydration for People with Urinary Diversion"
- National Academy of Sports Medicine: "What Are You Drinking?"
- University of Rochester Medical Center: "Hypoglycemia"
- Columbia University: "Go Ask Alice: Nausea From Weightlifting"
- American Council on Exercise: "6 Great Pre-workout Snacks"
- Johns Hopkins Medicine: "Exercise-Related Heat Exhaustion"