Everyone feels extremely tired at some point in time or the other but the fatigue may be real or perceived.

Real fatigue occurs when despite the brain issuing commands to a muscle, it refuses to follow through with appropriate and satisfactory action. This can occur if the nerve linked to the muscle is affected and there is total or partial paralysis, which can be caused by a stroke or injury or a viral infection such as polio. Then, one side of the body or one group of muscles is selectively affected.

There may be symmetrical weakness of either or both the upper and/or lower limbs if the cause is a metabolic disease such as diabetes or due to a malfunctioning thyroid, myasthenia gravis, alcoholism, drugs, vitamin deficiency (commonly of Vitamin D3 ) and mineral deficiency or excess (calcium, magnesium, sodium, potassium ). Fatigue can also occur in muscular dystrophy. These are a group of inherited diseases where the muscles slowly become weaker. Quite often the “limb-girdle” muscles are affected first, making getting up from a sitting position or climbing stairs difficult. Gradually, the muscles required for respiration and even the heart muscles can be affected. The commoner forms of this disease affect boys through the X chromosome inherited from the mother. The mother herself, however, is a carrier and does not manifest the disease.

Perceived weakness and fatigue should not be dismissed out of hand. Initial simple blood tests such as for blood sugar, thyroid levels, vitamin and mineral values should be done. An enzyme called creatinine kinase is elevated in muscular dystrophy. Usually, the diagnosis can be made at this point. Otherwise further tests such as imaging and muscle biopsy may be needed.

True muscle weakness can also occur where the muscle is normal at rest but contracts with less than anticipated force when asked to do any work or gets fatigued unusually fast when stressed.

It can occur especially with myasthenia gravis or muscular dystrophy.

In around 75 per cent of people, there is no disease process. The weakness and fatigue occur because of deconditioning or wasting of muscles. Muscles remain in robust health and top condition till around the age of 30. Then we gradually start to lose muscle mass in a process called sarcopenia. Often, people remain unaware of the loss of muscle mass, fibres and function until around the age of 60 or 70 years. They suddenly discover that they are unable to walk fast, climb stairs or lift light loads such as shopping bags.

This occurs at more rapidly in people who do not walk for 40 minutes a day, do weight training, balance, flexon and stretching exercises. Some medicines such as corticosteroids and the statins (to lower cholesterol) affect muscle strength adversely in some people. The pain of an old injury or arthritis may stop a person from using some muscles effectively and these will waste away. Overactivity of the compensation muscles can result in poor posture, instability, increased pain, disuse and more weakness.

Lack of restful sleep as well as depression may gradually decrease activity and cause muscle weakness. Heart failure can reduce the efficiency of the heart pump. Blood supply to the muscles then gets affected and they tire easily and become weak.

If muscle weakness is due to a correctable cause such as diabetes, heart failure, sleep disorders or a condition like myasthenia which can be treated, removing the cause will improve the condition to some extent. The age-related sarcopenia will progress but the rate can be slowed with exercise. Muscle weakness due to any cause responds to weight training and structured activity. The improvement may is gradual but is sustained.