Muscle weakness often happens after intense physical activity, such as heavy weightlifting at the gym or performing the same movement for a long time. In these cases, the weakness usually affects certain areas like the legs, arms, or chest, depending on which muscles were used the most.

This occurs because muscle fibers suffer small injuries and need time to recover, making it harder to maintain strength. Resting the affected muscles usually helps relieve the weakness and restores energy. That’s why it’s important not to train the same muscle group on consecutive days, allowing it enough time to recover properly.

However, there are many other possible causes of muscle weakness, including common illnesses like colds or the flu, which can make the whole body feel tired. While most causes are mild, sometimes the weakness can indicate a more serious condition that needs medical evaluation, especially if it lasts longer than three or four days.

What causes muscle weakness?

Muscle weakness can be caused by:

1. Lack of physical activity

When a person leads a sedentary lifestyle, spending long hours sitting at work or at home watching TV, the muscles gradually lose strength because they’re not being used. Over time, the body begins to replace muscle fibers with fat, reducing their ability to contract efficiently.

This cause is also common among older adults and people who are bedridden, often leading to a noticeable decrease in muscle mass and difficulty performing tasks that used to be easy.

What to do: whenever possible, include regular physical activity like walking, light jogging, or strength training at least two to three times a week. Bedridden individuals should do simple in-bed exercises to help keep muscles healthy and strong.

2. Natural aging

As people age, muscle fibers naturally lose some of their strength and elasticity, even in older adults who stay active. This can lead to a gradual feeling of overall muscle weakness that worsens over time.

What to do: continue exercising regularly but limit activity to what your body can handle. Alternate workout days with rest days to give the body time to recover and avoid injuries. Activities such as walking, light stretching, or swimming are especially beneficial for seniors.

3. Low calcium and vitamin D levels

Calcium and vitamin D are essential for proper muscle function. When these nutrients are too low, it can cause ongoing muscle weakness, along with symptoms like muscle spasms, tingling, irritability, and mild memory issues.

What to do: vitamin D is produced in the body through regular sun exposure, while calcium is found in foods like milk, cheese, yogurt, broccoli, and spinach. If blood tests show deficiencies, the doctor may recommend specific supplements for calcium or vitamin D.

4. Cold and flu

Muscle weakness and fatigue are very common during viral infections such as the flu or the common cold. This happens because the body uses more energy to fight off the virus, leaving less energy available for muscle function. In some people, the weakness may feel stronger due to inflammation or fever.

Other types of infections, such as hepatitis C, tuberculosis, Lyme disease, malaria, HIV, or dengue, can also cause similar symptoms.

What to do: if a cold or flu is suspected, rest at home, drink plenty of water, and avoid tiring activities like working out. If weakness does not improve or you develop a high fever and other concerning symptoms, consult a doctor to rule out more serious conditions.

5. Use of antibiotics and other medications

Certain antibiotics, such as ciprofloxacin or penicillin, and other drugs like anti-inflammatory medications or cholesterol-lowering agents (statins), can cause fatigue and muscle weakness as side effects.

What to do: talk to your healthcare provider before stopping or changing any medication. It is especially important not to discontinue antibiotic treatment without your doctor’s advice, as doing so could interfere with recovery.

6. Anemia

Anemia is a common cause of fatigue and can also lead to muscle weakness in more severe cases, making it harder to move the arms or legs. This happens when the level of red blood cells drops too low, reducing oxygen transport to the muscles.

What to do: anemia is more common in pregnant women and people who don’t eat meat. If you suspect anemia, see your doctor for a blood test to check your red blood cell count and start the appropriate treatment, which may include iron supplements or dietary adjustments.

7. Depression and anxiety

Mental health conditions can strongly affect energy levels and physical well-being. People living with depression often feel low in energy, which can lead to muscle weakness throughout the day.

In anxiety, adrenaline levels are often constantly high, making the body feel tense and tired over time, resulting in excessive weakness.

What to do: consult a psychologist or psychiatrist to determine if treatment is needed. Therapy and, in some cases, prescription medications like fluoxetine or alprazolam may be recommended by a qualified professional.

8. Diabetes

Diabetes causes high blood sugar levels, which can interfere with normal muscle function and reduce strength. When blood sugar levels stay elevated over time, nerve damage can occur, leading to muscle atrophy and weakness.

Common symptoms of diabetes include excessive thirst, dry mouth, frequent urination, and slow-healing wounds.

What to do: visit a general practitioner or endocrinologist for blood tests to check glucose levels. If diabetes is confirmed, follow your doctor’s recommendations, which may include dietary changes, regular exercise, and treatments such as metformin or insulin.

9. Heart disease

Certain heart conditions, like heart failure, reduce blood flow and oxygen supply to the body. When less oxygen reaches the muscles, they can’t contract properly, making everyday tasks like climbing stairs or walking longer distances more tiring.

This situation is more frequent after age 50 and often comes with symptoms like shortness of breath, swelling in the legs, palpitations, or frequent coughing.

What to do: if heart disease is suspected, see a cardiologist for diagnostic tests such as an electrocardiogram or echocardiogram to identify any abnormalities and determine the appropriate treatment.

10. Respiratory problems

People with respiratory conditions like asthma or chronic obstructive pulmonary disease (COPD) often experience muscle weakness more easily. During or after episodes of shortness of breath, oxygen levels may drop, and muscles don’t receive enough oxygen to function properly.

What to do: follow your doctor’s prescribed treatment plan and rest whenever muscle weakness appears. If you don’t already have a diagnosed condition but experience shortness of breath, see a pulmonologist to undergo the necessary tests and begin proper treatment.