Often, the difference between muscle fatigue and weakness involves overusing a particular muscle group or a disease or infection that involves the muscles. Fatigue and weakness both bring the same symptoms, so self-diagnosing and differentiating between the two can become difficult. During strenuous exercise, muscles can become fatigued for a short time, but this is usually only a temporary side effect. Weakness in the muscle groups that lasts for a longer amount of time can sometimes signify muscle disease, or at the very least a weakness that stems from improper use of the muscle group.
When an individual participates in a strenuous exercise program that exhausts particular muscle groups, like in strength or resistance training, muscle fatigue and weakness can occur simultaneously. In individuals who exercise regularly, fatigue often lasts only for a short amount of time and long-term muscle weakness is rare. Both might last for a longer period in individuals who improperly use muscle groups during exercise, and these side effects are often treated with adequate rest. It is often advised that an individual, regardless of the level of fitness, should not exercise the same muscle group every day.
Chronic muscle fatigue syndrome may also be a culprit in the link between the two, as this fatigue lasts for longer periods of time and is not relieved by rest alone. Fibromyalgia is a condition that includes severe muscle fatigue over time, and often results in weakness in many different parts of the body. Muscle weakness, rather than fatigue, usually involves temporary or long-term loss of function of a particular muscle group due to a disease or infection. If muscle weakness extends for a long time, an individual should seek medical attention, as this may be the symptom of a spinal cord injury or heart attack.
The differences in treatment between muscle fatigue and weakness vary greatly, but can also be related depending on the condition that brings on these symptoms. Usually, fatigue can be treated with adequate rest of the muscles, along with a healthy diet and a gentle exercise program. Muscle weakness, on the other hand, can also be treated with rest, or if more severe or chronic, then gentle exercise and prescription medications may be advised, especially if the condition is brought on by a thyroid or hormonal disorder. Both of these conditions can often signal that a muscle disease, in response to a virus or infection, is attacking the muscles, making symptoms that continue for more than a few days important to address.