Muscle Fatigue Symptoms

Muscle fatigue is the condition that denotes a decrease in the force exerted by the muscles involved in a physical activity. This article provides a brief overview about the condition, its causes and symptoms.
HealthHearty Staff
Last Updated: Apr 23, 2018
According to a recent study, muscle fatigue during intense physical activities is caused by leakage of calcium inside the muscles. This in turn activates an enzyme that damages the muscle fibers.

While working out for an extended period, you may feel exhausted and weak. You may not be able to work out at the same pace. This occurs when your muscles fail to generate enough force. This condition is called muscle fatigue. The muscles may regain their strength within some time, without hampering the ongoing physical activity. Otherwise, they become normal after sufficient rest. Generally, muscle fatigue caused by exercises is not considered a cause of concern, unless the condition does not normalize after proper rest. So muscle fatigue can be defined as a condition, wherein the muscles get tired to such an extent that they fail to exert a normal force, or require greater efforts to exert a normal force.
Muscle fatigue is of different types. It may affect the whole body, and is often described as an overall feeling of low energy. This type of muscle fatigue is called central muscle fatigue. Another type is peripheral muscle fatigue that affects a single muscle or a group of muscles, thereby causing a localized inability. There is a third type called neuromuscular fatigue that may fall under both the categories mentioned above.
What Causes Muscle Fatigue?
Role of Brain and Nerves: It is the brain that controls the voluntary movements that take place in the body. The movements of the muscles are also controlled by the brain, which sends nerve impulses to the muscles. Even the number and force of contractions are determined by the brain. The muscle cells contract, when they receive the signal from the brain and release calcium. So an impairment to the brain or the nerves may cause muscle fatigue.
Problems Within the Muscles: In most cases, muscle fatigue is caused by problems that arise within the muscles. Muscles require some sort of energy to contract. They use ATP, glycogen, etc., for this purpose. If they run out of these fuels, the muscles fail to generate enough force, thereby leading to fatigue. Sometimes, accumulation of waste products in the muscle fibers affect their functioning. These are the common factors that cause a decline in the force of muscle contraction, a condition that is termed metabolic fatigue.
While peripheral muscle fatigue is mostly associated with metabolic fatigue, central muscle fatigue is said to be caused by a reduced neural drive. A reduction in the neural drive causes a decline in the ability of the muscles to generate force. Studies show that, such reduction in neural drive actually helps to protect the muscles from injuries that can be caused by overuse. Neuromuscular fatigue is caused when the nerves that control the muscles fail to stimulate the muscles to contract. This condition is mostly seen in people with neuromuscular diseases, like myasthenia gravis.
Usually, exercise-induced muscle fatigue is associated with metabolic fatigue, and the condition subsides with sufficient rest. This is considered normal muscle fatigue. In some cases, strenuous workouts may lead to excessive muscle fatigue. The body may not be able to recover from such a condition, and this may lead to muscle damage. This condition is considered abnormal muscle fatigue. Prolonged stress, lack of sleep, regular smoking, and excessive alcohol consumption, are factors that may contribute to muscle fatigue. Even an unhealthy diet that lacks necessary nutrients, may lead to this problem.
There are several genetic as well as acquired medical conditions that can cause muscle fatigue symptoms. Such causes can range from cold and influenza, to thyroid problems and fibromyalgia. Others include cerebral palsy, anemia, chronic fatigue syndrome, myasthenia gravis, Addison's disease, botulism, lung cancer, and amyotrophic lateral sclerosis. Sudden muscle fatigue on one side of the body is usually associated with stroke. Even depression, anxiety and other such mental problems can lead to this condition. Intake of certain medicines may also contribute to muscle fatigue.
Symptoms and Signs
While an overall feeling of low energy is termed muscle fatigue, localized muscle fatigue is also very common. For example, leg muscle fatigue symptoms may include weakness in the legs and inability to achieve the desired movements. In general, muscle fatigue may be accompanied with a lack of enthusiasm, irritability and drowsiness. Some people may develop sore muscles, loss of appetite, difficulty in concentrating, and memory problems. The person gets tired easily, and may develop shortness of breath during physical activities. In some cases, muscle twitching may also occur. As far as athletes are concerned, muscle fatigue may cause a decline in their performance. Conditions that cause loss of skeletal muscle tissues (like, chronic kidney failure, muscular dystrophies, burns, sepsis, etc.) are also associated with muscle fatigue. People with such conditions develop muscle fatigue easily.
Muscle fatigue may affect movements of the associated joints. Overusing a fatigued muscle may result in further damage. Such a muscle injury takes some time to heal, and this causes a decline in the level of performance. On the basis of a study conducted in a group of young and old healthy adults, it has been suggested that older adults with muscle fatigue may compensate the discomfort with faster walking and longer strides. Even though, the symptoms of muscle fatigue are almost similar in men and women, females are more vulnerable to develop this condition during pregnancy. Muscle fatigue in women is mainly associated with conditions, like fibromyalgia and chronic fatigue syndrome.
Usually, muscle fatigue reverses with some rest, unless it is associated with some injury or underlying medical conditions. The muscle retains its power after a period of rest. The duration of that period is based on the severity of fatigue, and its underlying cause. Medical attention must be sought, in case of intermittent, persistent, or severe muscle fatigue.
Disclaimer: This article is for informational purposes only and should not be used as a replacement for expert medical advice. Visiting your physician is the safest way to diagnose and treat any health condition.