Distrofia Muscular

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Recommendations to Define Exercise Prescription

for Duchenne Muscular Dystrophy

Robert W. Grange and Jarrod A. Call

Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University,

Blacksburg, VA, United States

GRANGE, R.W., and J.A. CALL. Recommendations to define exercise prescription for duchenne muscular dystrophy. Exerc.

Sport Sci. Rev., Vol. 35, No. 1, pp. 12Y17, 2007. Duchenne muscular dystrophy yields pervasive and progressive muscle weakness.

This weakness may be attenuated by regular, low-intensity exercise. However, there is a critical lack of data to support appropriate

exercise prescription. Because inappropriate activity may exacerbate the dystrophic process, a systematic analysis of muscle function

to determine potential exercise load thresholds to avoid injury in dystrophic mice and dogs, and then in humans, is recommended.

Key Words: muscle injury, mdx mice, mdx:utrophin-/- mice, exercise prescription

INTRODUCTION

Muscular dystrophy describes a group of approximately 40

inherited heterogeneous disorders characterized by progressive

muscle weakness and muscle wasting (6). Duchenne

muscular dystrophy (DMD) is the most severe and fatal,

affecting 1/3500 boys (7). DMD is characterized by progressive

loss of contractile function caused by the absence of

the membrane-associated protein, dystrophin, and the associated

proteins of the dystrophin glycoprotein complex (6).

However, at present, the specific pathophysiological mechanisms

that lead to onset of the disease have not yet been

clearly defined.

DMD is an X chromosomeYlinked recessive disorder only

affecting the male population, although some female carriers

are mildly affected. DMD has a childhood onset and often

occurs in children within the same family. Coincident with

progressive muscle weakness is a gradual increase in the size

of many affected muscles known as pseudohypertrophy. The

later stages of the disease are characterized by abundant

fibrosis and adipose tissue within the muscle (7). Therapeutics

that are currently being used and developed for DMD

include drug and gene interventions. Although some drugs

are already being used to treat DMD patients (e.g., prednisone),

gene therapy has been limited to animal models.

Because DMD is characterized by weak muscles, and overload

resistance training is known to improve muscle strength, this

should be a suitable therapy. For example, exercise has been

used effectively to attenuate the loss of muscle strength and

endurance with aging, but is there sufficient data in the

literature to justify a sound exercise prescription to blunt or

reverse the effects of DMD? Unfortunately, none. Limited use

of exercise has been reported for patients with muscular

dystrophy for approximately 50 yr, and is considered to be

beneficial by some if performed at low intensity (2), but

definitive human studies on the use of exercise as a treatment

have not been conducted (Fig. 1). Determining the parameters

of exercise prescription is not a simple case of assessing

various training paradigms to improve muscle strength in

those with DMD because exercise itself could exacerbate

muscle damage. Thus, the limits to improve muscle function

and minimize muscle damage must be carefully established.

The purpose of this article is to propose that the exercise

prescription necessary to improve strength and muscle

endurance needs to be determined for individuals with

DMD. It is suggested that a systematic analysis in dystrophic

mice to establish musclefunctional capabilities and

adaptations may be the safest approach to define the fundamentals

of this exercise prescription.

DMD AND PHYSICAL ACTIVITY

Exercise, if properly prescribed and performed, is known to

improve physiological capacities of muscle such as strength

12

ARTICLE

Address for correspondence: Robert W. Grange, Ph.D., Department of Human

Nutrition, Foods and Exercise, Wallace Hall 321, Virginia Polytechnic Institute and

State University, Blacksburg VA 24061-0430 (E-mail: [e-mail]).

Accepted for publication: June 26, 2006.

Associate Editor: Gordon L. Warren, Ph.D.

0091-6331/3501/12Y17

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