Exercise as it relates to Disease/The effects of strength training on patients with muscular dystrophy

An image of normal muscle tissue in comparison to Muscular Dystrophy affected muscle tissue.

Background

What is Muscular Dystrophy?

Muscular Dystrophy (MD) is a genetic, degenerative disease characterised by progressive skeletal muscle weakness, defects in muscle proteins and the death of muscle tissue and cells. In affected muscles, tissues become disorganised resulting in a reduction in the concentration of dystrophin. Dystrophin is a protein found in the muscle fibre membrane and has a helical nature allowing it to absorb shock and return back to its original shape after it has been stressed. Dystrophin is an integral protein in linking actin dystroglycans of the muscle cell plasma (the sarcolemma) and also plays an important role in regulating calcium levels.

Who does Muscular Dystrophy affect?

Within Australia, there is approximately 30,000 people suffering some form of the neuromuscular disease. Prognosis for Muscular Dystrophy depends on the type and the progression of the disease. Cases may be mild and progress slowly throughout ones lifespan, and others may quickly suffer severe debilitating effects.

What are the types of Muscular Dystrophy?

Major forms of MD include:

Type of Muscular Dystrophy	Brief Description
Duchenne	The most common type of MD primarily affecting boys. DMD symptoms often start between ages 2–6. High risk of additionally developing scoliosis from wheelchair usage.
Becker	BMD affects boys and is similar to DMD but symptoms appear later and often less severe. Patients can have breathing, heart, bone, muscle, and joint problems.
Emery-Dreifuss	Symptoms appear late childhood/early 20s and primarily affect boys. EDMD involves muscles in the shoulders, upper arms and shins, often causing joint problems.
Limb-Girdle	Weakening of muscles in the shoulders, upper arms, around the hips and thighs.
Facioscapulohumeral	Weakening of muscles in the face, shoulders and sometimes lower legs. This form of MD has varying severity.
Myotonic	Muscles have difficulty relaxing, causing problems for muscle weakness, wasting (shrinking over time), cataracts and heart problems.
Congenital	Symptoms are shown in babies and children, involving muscle weakness and poor muscle tone.
Oculopharyngeal	Age of onset is much later in life (40-70yrs). Symptoms primarily affect muscles of the eyelids, face and throat, followed by pelvic and shoulder weakness.
Distal	Affects adult men and women, causing weakness and wasting of distal muscles (forearms, hands, feet, lower legs). Generally less severe and slowly progressing.

Exercise Prescription

There is an ongoing debate surrounding muscle training and its benefit for patients suffering Muscular Dystrophy. With an absence of effective therapies, patients suffering Muscular Dystrophy are reliant on symptomatic treatment, by which physiotherapy plays a significant role. There is an increased need for research on short and long term effects of muscular training to determine whether endurance, strength or combination exercise is preferred.

Benefits of Strength Training

• High-resistance strength training can be beneficial for slowly progressive MD (long-term effects undetermined at present).
• Initial muscular strength and endurance training shows improvements regardless of the type of MD.
• Increased muscle strength correlates with and increased level of muscle function.
• Patients with "limb-girdle" and "facioscapulohumeral" dystrophy derive the greatest physical and functional benefit from a strength program.

Exercise Recommendations

Creating an exercise prescription for patients with any form of Muscular Dystrophy requires a primary focus on gaining muscle strength and endurance in the early stages of the disease. Exercise will not cure Muscular Dystrophy, however it is suggested to decrease the speed at which the muscles will waste. It is important that close attention is paid to flexibility in order to prevent contractures.

Activity Type	Prescription	Goals
Aerobic Exercise	4–6 days per week Heart Rate of 50-80 percent of maximum 20–40 minutes per session	To maintain and increase aerobic capacity and decrease cardiac risk factors.
Flexibility	To be performed daily Each stretch held for approximately 20 seconds per	To increase patients range of motion and prevent contractures (a common association with MD).
Strength Training	Start at 50% of 1RM for more than 10 repetitions Gradually increase the percentage of 1RM as tolerated over a period of weeks to months. Strength training should be no longer than 1 hour per session	To improve functional strength, quality of everyday activities and decrease the symptomatic effects associated with MD.

Exercise Considerations

• A resistive exercise program in muscular dystrophy is most effective if instituted early in the course of disease.
• Ensure to allow for adequate rest when undergoing resistance activity.
• The loss of isometric and isokinetic strength will parallel the loss of functional capacity.
• Ensure patients “listen to their body” and decrease intensity if muscle cramps are present.
• Activity specific tasks should be integrated into a program (i.e. wheelchair propulsion) to enhance proficiency of daily living.
• Every case and strength training adaptations will be different.
• High-resistance training for rapidly progressive dystrophies is questionable and should only be commenced in the early stages of the disease (when a substantial amount of trainable muscle fibres is present).

Further reading

• Muscular Dystrophy Australia - http://mdaustralia.org.au/
• Better Health: Muscular Dystrophy - http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Muscular_dystrophy_explained
• WebMD: Understanding Muscular Dystrophy - http://www.webmd.com/children/understanding-muscular-dystrophy-basics