Muscle weakness is defined as a loss of strength in the muscles that results in inability to do specific tasks. It must be distinguished from fatigue, which is a feeling of tiredness.
Muscles are activated by nerves, with one of the steps involving release of chemicals at the neuromuscular junctions (NMJs) where nerve cells interface with muscle fibers. Nerve signals for muscle movement arise in the brain or spinal cord (reflex movements) and travel through cranial nerves to muscles in the head and neck and through the spinal cord and peripheral nerves to muscles of the body. Muscle weakness can result from damage to nerves, alterations at the NMJ, or damage to muscles.
What types of muscle weakness can occur?
The most common cause of generalized muscle weakness is prolonged inactivity, such as from bedrest or a sedentary lifestyle.
Sudden loss of muscle function is usually due to nerve trauma and requires immediate evaluation. Specific causes include infarction in the brain (stroke) or spinal cord and trauma (tearing, stretching, severing) or compression of the spinal cord or spinal nerves. A lesion in the base of the spine, called the cauda equina, causes loss of function of smooth muscles in the bladder and bowel and sudden incontinence.
Relatively rapid onset of muscle weakness and other symptoms is typical with infection such as varicella zoster, syphilis, poliomyelitis, diphtheria, Guillain-Barre, HIV, Lyme disease, botulism or a brain or spinal cord abscess. Inflammatory causes of nerve damage include diabetes mellitus and vasculitis.
Developing more slowly, chemical causes of muscle weakness due to nerve damage include vitamin (thiamine, B6, B12) or mineral (copper, phosphorus, potassium) deficiency; heavy metal (e.g., lead), alcohol, or organophosphate poisoning.
Progressive muscle weakness can be seen as the result of diseases such as the various myopathies, Myasthenia Gravis and ALS, among others – as well as diseases of the brain and spinal cord such as MS and tumors.
Muscles weakened by disuse can often be strengthened by a planned program of physical conditioning and exercise.
Treatments for other causes of muscle weakness depend on the mechanism and severity of injury and usually include medications or surgery. Physical therapy and exercises are also important in these cases to rebuild muscle strength and flexibility and prevent painful contractures.
While muscles like the gluteals are used any time we walk or climb a step, deep back muscles and abdominal muscles are usually left inactive and unconditioned. Unless muscles are specifically exercised, back muscles and abdominal muscles tend to weaken with age. Trust the doctors at the Florida Spine Institute to get you on the right path to better muscle strength.