Medical News Today: What causes dizziness after a workout?

Possible reasons for feeling dizzy after a workout include:

1. Overexertion

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Overexertion may cause a person to feel dizzy after a workout.

Overexertion occurs when people push themselves too hard during physical activity. Signs of overexertion include:

  • dizziness
  • feeling faint
  • lightheadedness
  • nausea
  • shortness of breath
  • thirst
  • vomiting

According to 2015 research, injuries related to overexertion account for 36.2% of all injuries occurring at fitness facilities.

Overexertion does not just happen in gyms or exercise classes, however. It can happen during any activity.

2. Use of continual motion machines

The type of exercise a person does may influence whether they feel dizzy. For example, using an elliptical machine or a treadmill, which both involve continuous movement, is more likely to cause dizziness.

Some people experience lightheadedness or dizziness when they step off the machine. They may feel like they are still moving when they are not.

This experience is called vertigo. Others experience dizziness as a symptom of motion sickness.

3. Dehydration

Dehydration occurs when the body loses more water than it takes in. Although dehydration is most common in children and older adults, it can affect people of any age.

Healthy adults are most likely to experience dehydration from a minor illness or intense physical activity, especially during hot weather.

Symptoms of dehydration include:

  • dizziness
  • dry mouth
  • extreme thirst
  • feeling faint or lightheaded
  • less frequent urination
  • tiredness
  • weakness

Even mild dehydration, which is a loss of just 1–2% of body weight, can cause these symptoms. Many people think that thirst is one of the first signs of dehydration, but by the time someone feels thirsty, they are already experiencing dehydration.

4. Lack of oxygen

Improper breathing during exercise means that some people do not take in enough oxygen to meet the needs of their muscles.

During exercise, muscles use more oxygen than usual. This is why heart rate and breathing become faster to facilitate a higher intake of oxygen.

People who do not breathe often enough or deeply enough can experience a lower-than-optimal level of oxygen in the brain. Dizziness is a sign that the brain requires more oxygen.

5. Low blood pressure

Blood pressure is the force of the blood that pushes against the artery walls. In most people, healthy blood pressure is less than 120/80 millimeters of mercury (mm Hg). People who have low blood pressure, or hypotension, will have a reading of less than 90/60 mm Hg.

Blood pressure is typically at its lowest within an hour of exercise. Some people may notice a more sudden drop, however.

In addition to dizziness, symptoms of hypotension include:

  • blurred vision
  • fainting
  • fatigue
  • loss of concentration
  • nausea

Vigorous activities most often cause low blood pressure, although any activity can trigger it. Some people with hypotension feel symptoms simply if they stand up too quickly.

Hypotension can be a cause of exercise-induced dizziness during pregnancy. It also results from dehydration, heart problems, and the use of certain medications.

6. Low blood sugar

Hypoglycemia, or low blood sugar, occurs when the level of glucose (sugar) in the blood is very low.

Sugar is the body’s primary energy source. During exercise, the muscles use more glucose than usual. As a result, some people experience low blood sugar during or after physical exertion.

Symptoms of hypoglycemia include:

  • dizziness
  • anxiety
  • clumsiness
  • fatigue
  • hunger
  • irritability
  • shaking
  • sweating

People may be more likely to experience hypoglycemia if they have not eaten much before exercising. This can be a common problem for those who exercise first thing in the morning.

7. Heart arrhythmia

A heart arrhythmia is an abnormal heartbeat. Arrhythmias may cause the heart to beat too quickly, too slowly, or irregularly. Many conditions can cause arrhythmias, including heart conditions and emotional stress.

Exercise can also trigger or worsen a heart arrhythmia, particularly in people who have heart disease.

Not all arrhythmias cause symptoms, but when symptoms do occur, they include:

  • dizziness
  • change in heartbeat
  • fainting
  • lightheadedness
  • shortness of breath
  • sweating

Even when symptoms occur, it does not necessarily mean that a person has a serious problem. However, it is always important to see a doctor for persistent arrhythmias.

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