Weakness refers to the inability of a muscle or group of muscles to contract with normal force, resulting in the inability to carry out the normal tasks associated with those muscles. A muscle might be normal in strength when performing a one-time task, but lose strength with repeated action. This is called muscle fatigue. Even normal muscles can become fatigued if they are overused. Low levels of fitness make the activities of all muscles more difficult to maintain. In this sense, fatigue can apply not just to one set of muscles, but to the whole body.

Poor sleep, hot weather, medical complications such as anemia and heart and lung disease, certain medications, and depression can add to becoming easily fatigued during daily activity, especially as the day wears on. There are many forms of fatigue: the development of actual weakness in a muscle or muscles, physiological lack of stamina, and psychological lack of energy. People with spinal cord injury (SCI) should try to describe their symptoms to the doctor so as to distinguish between weakness and fatigue, and between the various forms of fatigue. This can be done by describing symptoms within the context of how the day is spent, in other words, the functions of daily living associated with fatigue.

What are the possible causes of fatigue?

  • Loss of Sleep. After SCI, sleep apnea is remarkably frequent. Breathing is repeatedly interrupted, the brain is robbed of oxygen, and sleep is not refreshing. This leads to general fatigue during the day. Urinary urgency and pain also interrupt sleep.
  • Heart and Lung Weakness. If shortness of breath with modest exertion accompanies fatigue, it can be a sign of a cardiac problem or a lung disorder. A physical exam and special tests to evaluate heart and lung function might be necessary. SCI patients should try to increase their exercise tolerance gradually by pushing their wheelchair, and by performing arm and leg exercises, whenever possible, in order to build up an energy reserve.
  • Decreased Muscle Strength. Many complications can further weaken muscle strength and functional use of the arms, trunk and legs. Some of the treatable causes are non-use of muscle groups because of joint pain, spasms, or dysreflexia; lack of an exercise regimen that aims to maintain or increase the reserves for activities; and syringomyelia.
  • Glandular and Hormonal Problems. Endocrine problems such as thyroid disease can weaken muscle.
  • Medications. Medications can also impair strength. For example, elevated cholesterol levels can accompany inactivity with genetic predisposition. The cholesterol- lowering statin drugs and other medicines can cause muscle damage (myopathy), with muscle weakness that can add to disability.
  • Aging. Problems that are common in anyone with aging, such as a peripheral neuropathy from diabetes or compression of a nerve root (radiculopathy) from a herniated intervertebral disk, can complicate the effects of SCI.

Actual weakness must be separated from a sense of fatigue, and difficulty in home and community activities from malaise, poor sleep, and depression. A doctor who is accustomed to managing people with SCI and other neurologic diseases might be needed to sort out these difficulties.