Muscular Dystrophy and Exercise
By: Margo Lewkow

Muscular dystrophy is a genetic disorder that gradually weakens the body's muscles. It is caused by incorrect or missing genetic information that prevents the body from making the proteins that it needs to build and maintain healthy muscles. A child who is diagnosed with muscular dystrophy loses the ability to do things like walk, sit upright, breathe easily, and move the arms and hands. This increasing weakness can lead to other health problems (1).

Duchenne MD is the most common form of MD and primarily affects boys. Onset is between 3 and 5 years old and the disorder progresses rapidly. Most boys are unable to walk by age 12, and later need a respirator to breathe. Girls in these families have a 50 percent chance of inheriting and passing the defective gene to their children (2). DMD is passed from mother to son through one of the mothers genes which is X-linked recessive. The defective gene that causes DMD is located on the X chromosome, meaning females are carriers of the disease and if their son receives that chromosome he will inherit the disease. In some cases DMD arises from a new mutation in a gene rather than from an inherited defective gene (3).

Along with weakening muscles, another symptom of DMD is an enlargement or overdevelopment of the calves, known as pseuodhypertrophy. Most people who exercise experience muscle hypertrophy, or muscle enlargement. People with DMD experience this, but instead of getting stronger DMD causes muscles to become permanently damaged. This happens because protein in the muscles is being replaced by fatty deposits. Other problems that may arise from DMD are lordosis, or curvature of the lumbar and cervical spine caused by weakening back muscles. Weak foot muscles cause the Achilles tendon to contract and pull the feet into an abnormal position which interferes with the ability to walk. Also a purple discoloration of the feet may occur. This happens as muscle function of the feet and legs decreases. Active muscles require blood flow, accordingly, the cardiovascular systems directs blood flow to the organs where it is needed most. Joint and tendon restriction, called 'contracture' may occur. It typically affects the ankles first, then the knees and hips, and finally the joints of the upper limbs. Due to protein abnormalities in the brain that cause cognitive and behavioral deficits, intellectual handicaps are more frequent in people with DMD than in the general population, but still only affect a small percentage. Respiratory muscle function may begin to decline. As DMD progresses the diaphragm becomes weak and breathing becomes difficult (4).

To diagnose someone for MD there are a series of tests that a doctor will perform to check for the disease. This includes a blood test to check levels of serum creatine kinase, which is an enzyme that is released into the blood when muscle fibers are deteriorating. Elevated levels of this enzyme indicate that something is causing muscle damage. A doctor may also do a blood test to check DNA for gene abnormalities, or a muscle biopsy to check muscle tissue for deterioration and abnormal levels of dystrophin, a protein that helps muscle cells keep their shape and length. Without this protein, muscles break down (1).

There is no cure for any type of muscular dystrophy, but there is extensive research that is focused on the treatment of this disease. Until a cure for DMD is found, treatment will involve the administration of corticosteroids combined with interventions to alleviate cardiac and respiratory problems. Corticosteroids act to preserve existing muscle fibers and reduce inflammation, although their exact mechanism of action in dystrophic skeletal muscle is unknown. Unfortunately there are side effects to taking these corticosteroids, which include increased appetite requiring strict dietary control, retarded growth resulting in short stature, and asymptomatic cataracts. Administering steroids is not a cure but can be a way to improve quality of life and prolong lifespan.

DMD is characterized by aggressive inflammation. There have been some studies done on anti-inflammatory drugs as a treatment for DMD. Though the use of highly specific anti-inflammatory drugs appears an attractive alternative to steroids, their potential to reduce the severity of DMD remains to be determined (5). Exercise in itself can be beneficial to people with muscular dystrophy, but severity of the disease, age of the person, and activity level must be closely monitored.

Some studies have found that the muscle of boys with DMD fatigued less than that of healthy boys, but others have reported that the fatigue in DMD and in normal muscle was the same. These conflicting results may be explained by methodological differences including the exercise models, the intensity of exercise, and the muscle groups investigated (6). Flexibility should be the primary focus of the exercise program. Stretching should consist of passive and active stretches. Care should be taken not to cause muscle damage; therefore ballistic stretching should be avoided. Stretching should focus on muscle groups prone to contractures, such as the hip, knee, shoulder, wrist, fingers, and plantar flexors.

Endurance exercise may be recommended for persons with DMD. Spontaneous walking speed should be the determination for the exercise intensity. Duration of exercise should be based on each individual's tolerance to exercise. Walking surfaces should be level to avoid the performance of downhill walking, which may cause excessive muscle damage due to the increased eccentric component; any activity that consists of changes in directional velocity can cause muscle damage. Swimming or cycling may also be recommended. Resistance exercise can increase the strength of people with MD, however, the eccentric component should be eliminated. This is eliminated when doing concentric only isokinetic exercise, or eccentric only isokinetic exercise, therefore possibly reducing muscle damage (7).

Children with MD may be excluded from many typical childhood experiences, including active recreation and physical activity. However, by participating in physical activity, individuals with MD are given an opportunity to acquire some physical skills and enhance social capabilities. The physical activity setting provides an environment in which the individual with MD can engage in common and expected childhood experiences (8). While the condition is in the early stages the patient should participate in games and athletics as much as possible. Sedentary recreational activities should be introduced which will carry over when the patient is in a wheelchair.

It is good to encourage movement and dance activities that allow the individual to express emotion. Also, encourage breathing games and exercises when the individual is confined to a wheelchair (9). When a wheelchair or braces are necessary, the physical design of sport equipment and the arrangement of playground settings may need to be modified (8). Wheelchairs are very helpful to people with MD for mobility and independence, but it is good to get them up and moving on their own as much as possible (10).

Aquatic activity has been successful in treating people with muscular dystrophy. Since water buoyancy decreases the negative effects of gravity, joints are supported and allow for increased freedom of movement and flexibility with reduced pain. Due to increased mobility, aquatic activity promotes improved circulation and improved respiratory functioning while helping to maintain heart rate. Water resistance prevents rapid movement while promoting muscle strength. Fun, relaxation, and increased freedom of movement (without crutches or wheelchairs) are a few of the psychological benefits of aquatic activity. Special care must be taken to not over fatigue the patient, engage in moderate levels of activity, build in frequent rest periods, and water temperature should be warm. The Delta Float System is a vinyl coated triangular shaped swim support system that provides support to the front and rear of the torso. With this device the person with MD can float and move around in the water while feeling supported. Sectional/ modular rafts allow for total body support in either supine or prone positioning, and frees the participant to move upper and lower extremities. A head float secures around the neck for support (11). It is important to allow the individual with MD to be in an aquatic environment as much as possible (9).

Aside form aquatics, there are many activities that people with MD can participate in. There have been skis designed for those with leg strength and stability issues. They provide the individual with four points of contact with the snow, and a variety of other stabilizing equipment (12). Hockey was created for those in wheelchairs. Players use a variety of sticks to play depending on their upper body strength and ability to grip the stick. Double Sticks are two sticks fastened together, with the blades forming a V, and are strapped to the player's legs and chair frame. Standard hockey rules are used with some slight variations (13). Other activities available to individuals with MD are wheelchair rugby, bowling, tee ball, tennis, and kickball to name a few. Individuals with MD have many options when it comes to participating in physical activity. The most important objectives to concentrate on are socio-emotional maintenance and development, development of balance and coordination, maintenance and possible improvement of strength and endurance, joint positioning and maintenance of flexibility, respiratory maintenance, weight control, and interpretive development (14). With a little imagination and creativity, it is possible to prolong and improve the quality of life for any individual diagnosed with muscular dystrophy.

references

1) kidshealth.org/parent/medical/bones/muscular_dystrophy.html (4/7/2007)
2) www.ninds.nih.gov/disorders/md/md.htm (2/13/2007)
3) www.mayoclinic.com/health/musculardystrophy (12/9/2005)
4)www.nlm.nih.gov/medlineplus (4/7/2007)
5) International Journal of Biochemistry and Cell Biology: volume 39, issue 3, 2007 p. 469-477 Radley, H.G.; DeLuca, A.; Lynch, G.S.; Grounds, M.D.
6) Sports Medicine: volume 36, issue 12, 2006 p. 1031-1065 Ratel, Sebastien; Duclie’, Pascale; William, Craig
7) www.ncpad.org/disability/fact_sheet.php?sheet=142 (3/1/2007)
8) Journal of Sport and Social Issues (200) Diane E. Taub; Kimberley R. Greer
jss.sagepub.com/cgi/reprint/24/4/395
9) http://twu.edu/INSPIRE/fact_sheet/muscdys.htm (4/7/2007)
10) www.blackwell_synergy.com (2005) C.L. Webb
11) http://eric.ed.gov/ERICWebPortal/Home.portal Aquatics and Persons with Disabilities/ PAM Repeater (06/1993)
12) www.adaptivesports.org (4/7/2007)
13) www.msu.edu/~pedrazaj/adaptedsports/sports.html (10/11/2006)
14) Applied Special Physical Education and Exercise Therapy: 4th Edition, 2005, Christine Stopka; John R. Todorovich

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