Spinal muscular atrophy (SMA) is an inherited condition that affects motor neurons, which are the nerve cells that control the movement of voluntary muscles. Their loss leads to progressive muscle weakness.

Fatigue in SMA

Fatigue is a state of physical exhaustion. It can decrease motivation and affect everyday activities, work, and social life.

Besides perceived fatigue, SMA patients also experience muscle fatigue. Muscle fatigue is usually defined as an exercise-induced decrease in the ability to produce force. In SMA, the term is used to describe muscle weakness and rapid exhaustion during daily activities.

Perceived fatigue in SMA is assessed using a fatigue severity scale based on a questionnaire, while muscle fatigue is measured by assessing muscle strength.

The fatigue severity scale questionnaire consists of nine questions about how patients perceive their fatigue and how it interferes with their daily activities. Patients rate how each statement applies to them on a scale from zero to seven, with seven indicating the strongest agreement. Higher numbers indicate a higher impact of fatigue on the patient. An overall score above four is considered disabling fatigue.

Reports about fatigue rates in SMA differ significantly. One study reported that 81 percent of SMA patients, including those with spinal and bulbar muscular atrophy, experience disabling fatigue. Another study that assessed the rate of disabling fatigue in patients with SMA type 2 found that it occurs in 10 percent of these patients. Symptoms can vary greatly between different types of SMA and even within specific forms, which might explain the discrepancy.

What causes fatigue in SMA?

Perceived fatigue does not always correlate with muscle fatigue in SMA patients. Perceived fatigue is a subjective impression that might be aggravated through the inability to perform everyday tasks, which is only partly caused by muscle fatigue.

It is not entirely understood what causes muscle fatigue in SMA. However, there is evidence suggesting that conduction blocks along nerve fibers may play a role. A conduction block is an area on the nerve fiber where the transmission of the nervous signal is interrupted. Muscle contractions are controlled by motor neurons that transmit electric signals. When a conduction block hinders the transmission, this might contribute to muscle fatigue.

Strategies to reduce fatigue


SMA patients report that exercise helps reduce fatigue. In general, exercise is known to increase energy levels and help maintain good health. In SMA, exercise is thought to slow the decrease in muscle force and improve motor function. Physical activity may, therefore, improve perceived fatigue and increase quality of life. It is recommended that exercise be tailored to patients’ abilities. A physiotherapist can help evaluate muscle and functional deficits and find suitable exercises for each patient.


Fatigue should not be confused with tiredness, but like tiredness, fatigue can be reduced with sufficient and recreative sleep. Daytime napping can help decrease fatigue that occurs toward the end of the day. Extensive napping can, however, be counterproductive because it decreases sleep quality at night.


SMA News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.