There are a large number of potential causes of muscle weakness and fatigue, including disease, a muscle pull or tear and overuse. Muscle weakness and fatigue are actually two different conditions, although they can be caused by similar problems in some cases. Other potential causes include a lack of minerals in the body, muscle wastage due to lack of use and nervous system conditions. In some cases, muscle fatigue may simply be caused by insufficient sleep or exhaustion, although long-term symptoms may be a sign of something more serious.

Muscle weakness occurs when the muscle isn’t able to provide its normal strength. This commonly occurs, for example, after a long workout in which the muscle becomes sore or tired for a period of time. This type of muscle weakness usually goes away naturally once the muscle has had time to recover.

True muscle weakness, where the muscle becomes permanently weak, is a more serious condition. If a muscle gets gradually weaker over time, this can be a sign of a number of health problems. These include an impairment in the nervous system that affects the signals to the muscle, diseases such as celiac disease and conditions such as fibromyalgia. In most cases, a gradual weakening of a muscle that’s being regularly used is cause for a visit to a medical professional for an evaluation.

Muscle weakness and fatigue, although similar, have noticeably different symptoms. Muscle fatigue is when the muscles feel tired or lack energy. This can be caused by the person being overworked, not getting enough sleep or general health problems, such as the common cold. Usually muscle fatigue will disappear when the problem is rectified. If, however, muscle weakness and fatigue doesn’t get better within a couple of weeks then a doctor should be consulted.

Some of the most serious causes of muscle weakness and fatigue include a disease to the liver or kidney; diabetes; and heart failure. Any condition that limits the blood flow to the muscle can cause a feeling of weakness. Issues with the thyroid are also known to cause muscle weakness and fatigue.

Sometimes a mental disorder can be the cause of muscle weakness and fatigue. For example, both chronic fatigue syndrome and fibromyalgia can cause these types of symptoms. Often, the weakness will be present for a long time, as the conditions can go undiagnosed for a relatively long period compared to other illnesses.