By Jennifer Green, MS
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| Jennifer Green, NCHPAD Visiting Information Specialist |
It is important to know and understand the process and patterns of weakness for the type of MD your client may have. For example, DMD progresses to involve distal muscles, at which time ambulation becomes more difficult. By the age of 10, most children with DMD use wheelchairs. Children with DMD often have normal strength until age 3-4, when progressive proximal weakness begins. Clients with FSHD may have completely normal handgrip strength and yet be unable to raise their arms above their heads; Facioscapulohumerol dystrophy is named after the muscles it most primarily involves: biceps, tibialis anterior, and thigh muscles. Expectedly, knee extension strength would be affected as well.
The loss of isometric and isokinetic strength will parallel the loss of functional capacity. Individuals that do not have other associated conditions usually have a normal heart rate, ventilation, and RPE at a given relative exercise intensity of cycling; however, the loss of strength renders the absolute values higher than those in age-matched controls. Alterations in gait patterns can lead to an abnormally high oxygen cost per unit of work, especially on the treadmill. For this reason, a cycle ergometer would be the most helpful in assessment and exercise prescription.
When creating an exercise prescription for individuals with muscular dystrophy, the primary focus should be on gaining muscle strength and endurance, while paying close attention to flexibility to aid in the prevention of contractures. Aerobic activities should be prescribed 4-6 days/week at 50-80% HRR for 20-40 minutes (with a goal >20 minutes). The goal of aerobic training should be to maintain and increase aerobic capacity and decrease cardiac risk factors. Several modes can be used depending on your client's ability, including cycling, walking, elliptical, rowing, wheeling, and arm ergometry. Flexibility exercises should be performed daily and held for about 20 seconds/stretch in order to increase range of motion and prevent contractures which are commonly associated with MD. Finally for strength training, it is important to start at a low (≈ 50%) percentage of individual 1RM and with more than 10 repetitions. Gradually increase the percentage of 1RM as tolerated over a period of weeks to months. When creating a program, allow for at least 48 hours of rest for a given muscle group and always tell your clients to "listen to their bodies" and to decrease intensity if mild myalgias do not disappear after 36 to 48 hours or if muscles cramp during an activity. When muscles are weaker than antigravity strength, formal weights are useless and the goal should become to exercise through an available range of motion, and then to regain full range against gravity. Functional or activity-specific tasks can also be included in a program (i.e., wheelchair propulsion) to maintain and enhance proficiency in activities of daily living. These activities should be performed daily as tolerated by the client.
There are several special considerations that should be kept in mind when working with a client who has any form of muscular dystrophy. The knowledge of characteristics of the specific dystrophy is extremely important in order to adapt the exercise testing and prescription to the individual. Cardiac problems such as cardiomyopathies (seen in DMD, BMD, and some forms of LGMD and EDMD) and cardiac conduction defects (can be seen with EDMD and myotonic MD) are very common in several forms of MD and can limit exercise capacity. It is suggested that clients consult with a cardiologist before an exercise test or prescription are created. Contractures are another important factor to consider when creating a program and may limit the ability to use certain modalities. The proper use of assistive equipment and creative planning on behalf of the personal trainer should be used to avoid a lack of motivation to exercise by the client. It is important to look at all aspects of each form of muscular dystrophy, including safety, exercise intensity, mode of exercise, and psychological and environmental aspects to ensure that the program is safe and effective.
Numerous studies show that physical activity can help improve strength and activities of daily living in those with MD. With the help of fitness professionals, appropriate programs can be created to increase muscular strength, endurance, and power as well as protect against other secondary or associated conditions.
References:
Markert, C. D. (2010). Exercise and Duchenne muscular dystrophy: Towards evidence-based exercise prescription. Medicine and Science in Sports and Exercise, 42(10), 29.
Simmonds, M. J., Ph.D., PT., MCSP., & Derghazarian, T. P. (2009). Muscular Dystrophy. In J. L. Durstine (Ed.), ACSM's Exercise Management for Persons with Chronic Diseases and Disabilities (3rd ed., p. 306). Human Kinetics.
Sveen, M. L. (2008). Endurance training improves fitness and strength in patients with Becker muscular dystrophy. Brain, 131(11), 2824.
Please send any questions or comments to Jennifer Green at Jennifer Green.