Sunday, November 3, 2013

MUSCULAR DYSTROPHY AND EFFECTS OF EXERCISE



Effects of Exercise on Different Muscle Diseases
by Margaret Wahl on April 1, 2009 

Disease category
Nerve or muscle problem
Implications
These are degenerative muscle diseases, meaning the normal ability of muscle to regenerate and repair damage is limited, resulting in a net loss of muscle tissue over time.
Some (BMD, DMD and some LGMD forms) involve fragile membranes around skeletal and/or cardiac muscle fibers.
Many muscular dystrophies (DMD, BMD, some LGMD, EDMD, myotonic MD) involve cardiac muscle deterioration or abnormal heart rhythms.
• Muscle fibers can be damaged by strenuous exercise, and the damaged sustained may be permanent.
• In DMD, BMD and the sarcoglycan-deficient LGMDs, exercise involving eccentric (lengthening) contractions is particularly damaging.
• If the heart’s pumping ability or rhythm is affected by the disease, sudden, strenuous exercise could trigger an acute heart problem, respiratory problem or even death. A cardiologist should be consulted before undertaking an exercise program.
Warning signs of an acute cardiac problem are chest pain, shortness of breath, nausea, sweating without strenuous exercise, a feeling of fullness or pressure in the chest, or a gurgling sound durinig breathing (a sign that fluid may be backing up into the lungs).
Disease category
Nerve or muscle problem
Implications
Nerve cells in the central nervous system (spinal cord and brain) that control muscle movement are lost, leaving muscles “orphaned” and undernourished.
• Theoretically, remaining nerve cells can become overburdened if too much is required of them with exercise.
Inflammatory Myopathies
dermatomyositis, polymyositis
Muscle fibers are attacked by the immune system, causing inflammation and tissue destruction.
• Exercise should vary with disease activity. During severe disease activity, when strength is very poor, assisted or passive range-of-motion exercise can be undertaken. During periods of mild to moderate disease activity, when muscles can work against gravity, light aerobic exercise, isometric strengthening, and active range-of-motion exercise are recommended. When the disease is inactive (in remission), recreational aerobic and progressive resistance exercise are OK.
Disease category
Nerve or muscle problem
Implications
Diseases of the Neuromuscular Junction
myasthenia gravis
Communication between nerve fibers and muscle fibers is compromised, in most cases by a mistaken attack on the neuromuscular junction by the immune system.
• Exercise can be undertaken when the disease is under good control. In periods of acute disease exacerbation, or when the disease is not well controlled, exercise may increase weakness.
• Exhaustion, lasting joint or muscle pain, or shortness of breath means the exercise is too strenuous.
• If on prednisone, mild exercise can help offset side effects, such as weight gain, bone loss, high blood pressure, high blood sugar, depression and anxiety.
Disease category
Nerve or muscle problem
Implications
In CMT, and DSS, nerve fibers and/or the insulation around them are abnormal, compromising communication to muscle fibers.
• Exercise is good for the heart and lungs but will not overcome muscle wasting, which is the result of damage to nerve fibers and loss of input from the nervous system.
• Low-impact exercise, such as swimming or biking, or yoga, is better than high-impact exercise
In FA, an abnormal cellular distribution of iron leads to diminished cellular energy production, with damage to the heart and nerves
• Moderate exercise may help slow the loss of motor skills in FA and help offset weight gain.
• Cardiac precautions apply. No exercise should be undertaken without consulting a cardiologist.
Disease category
Nerve or muscle problem
Implications
Processing of fuel (carbohydrates or fats) in muscle fibers is inadequate, leading to subnormal energy production and/or a toxic buildup of fuel.
• Muscle fibers may break down in an attempt to meet the energy requirements of exercise.
• Do not engage in aerobic exercise that causes the heart rate to exceed 65 percent of maximum (220 minus age, multiplied by 0.65).
• Light resistance exercise, such as lifting no more than 5 to 10 pounds, can help build muscle mass.
• Warning signs to stop are pain, muscle tightness or cramps, exhaustion or cola-colored urine. Seek medical help if urine turns dark.
• If the heart is involved, cardiac precautions apply.
Disease category
Nerve or muscle problem
Implications
Ion Channel Diseases
paramyotonia congenita, periodic paralysis (hypokalemic & hyperkalemic)
Channels in muscle fibers that allow the passage of sodium or calcium are abnormal.
• People with periodic paralysis benefit from good fitness. However, vigorous exercise followed by rest can precipitate a bout of weakness or paralysis. (In hyperkalemic PP, attacks generally occur within an hour of exercising. In hypokalemic PP, they’re more likely to occur the morning after exercise.)
• Low-intensity exercise is best. Some people find they can ward off weakness by cooling down slowly.
• In paramyotonia congenita, muscle cooling can increase myotonia (inability to relax muscles) and transition into weakness and paralysis.
• If swimming, particularly in cold water, paramyotonia congenita patients are at increased risk of an attack and of drowning.
Centronuclear Myopathies
myotubular myopathy, autosomal centronuclear myopathies
Muscle fibers show centrally placed nuclei, in contrast to their normal position, which is around the periphery (edge) of each fiber. Mutations in genes for the muscle proteins myotubularin, dynamin 2, MYF6, amphiphysin 2, and probably others result in weakness, the precise cause of which remains uncertain. Outcomes range from severe weakness affecting all muscles, including those involved in breathing, to weakness so mild it leads only to poor athletic performance.
Because these conditions are not progressive and don’t have specific defects in the muscle fiber membrane that lead to its fragility, exercise is likely safe if the myopathy is not too severe. Check wih your doctor before beginning an exercise regimen. There are no data on exercise for children with severe centronuclear myopathies, such as the X-linked, myotubularin-related type.

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