Feeling sick after exercise? Experts explain surprising reason

Feeling nauseous after an intense workout is more common than many people realise, and experts say it often happens because the body redirects blood away from the digestive system to fuel working muscles.

According to experts who spoke to Health, factors including exercise intensity, dehydration, hot weather and meal timing can all contribute to post-workout stomach discomfort.

Why exercise can upset your stomach

During moderate to vigorous exercise, blood is redirected towards the muscles, heart, lungs and skin, reducing blood flow to digestive organs such as the stomach and intestines.

Dietitian and certified personal trainer Maxine Yeung explained that this reduced blood supply slows digestion and can trigger symptoms including nausea, bloating, cramping, vomiting and diarrhoea.

The longer a person exercises at moderate or high intensity, the longer blood flow to the digestive system remains reduced, increasing the likelihood of stomach issues.

Certain workouts carry a higher risk

Experts say almost any exercise can cause nausea if the body is unprepared for the intensity or duration, but some activities are more likely to trigger symptoms.

Running, sprinting, HIIT, cycling, rowing and swimming sessions that involve repeated high-intensity efforts with short recovery periods can place greater stress on the body.

Running may be especially problematic because, in addition to reduced blood flow, the repeated impact causes the stomach contents to move up and down, increasing pressure on the digestive system.

Heat and dehydration worsen symptoms

Exercising in hot or humid conditions increases sweating, making dehydration more likely.

Yeung noted that dehydration is a common cause of nausea during exercise, particularly during long workouts or in high temperatures.

Experts also say dehydration may trigger hormones involved in maintaining fluid balance that can contribute to feelings of nausea.

Meal timing matters

Eating too much shortly before exercising can leave food sitting in the stomach, increasing the risk of nausea, bloating and discomfort.

Meals high in fat, fibre or large amounts of protein take longer to digest and may worsen symptoms during exercise.

Experts recommend eating a full meal at least three hours before a workout or choosing a light carbohydrate-rich snack, such as toast or a bagel, one to two hours beforehand.

How to reduce workout-related nausea

Experts recommend warming up gradually before intense exercise, staying well hydrated, adjusting workout intensity when necessary and experimenting with meal timing to determine what works best for your body.

For workouts lasting longer than an hour, replenishing fluids and carbohydrates with sports drinks or energy gels may also help reduce nausea and support recovery.