Section Information: Abstracts of Platform and Poster Presentations for the 2005 Combined Sections Meeting: Poster Presentations
BACKGROUND AND PURPOSE: Duchenne Muscular Dystrophy (DMD) is characterized by a progressive loss of strength due to skeletal muscle fiber destruction. The primary abnormality is a lack of the protein dystrophin, which normally plays a role in the structural integrity of the plasma membrane. There is limited research regarding the benefits of exercise for children with DMD. While eccentric exercise has been shown to be detrimental in animal models and should be avoided, concentric exercise may be beneficial in maintaining muscle strength. Two case studies were completed in order to determine the effect of a three-month resistance exercise protocol for children with DMD.
CASE DESCRIPTION: Two boys with DMD participated in a program of maximal effort concentric knee extension and flexion resistance exercise. The child and one parent were instructed and demonstrated competence in the exercise program. Subject 1 was 9 years, 4 months, and Subject 2 was 6 years, 5 months. The exercise program consisted of the child sitting in a chair, performing concentric knee extension and flexion using medium resistive elastic exercise band for resistance. Children completed 10 repetitions for each leg three times per week. Outcome data consisted of peak isometric knee extension and flexion torque with the knee positioned at 60 degrees of flexion.
OUTCOMES: Subject 1: After two weeks of exercise, isometric torque increased. Knee extensors increased from 11.6 to 14.4 Nm (+24%), and flexors increased from 10.9 to 11.4 Nm (+4%). After 14 weeks of exercise, extensor and flexor torque decreased to approximately baseline or slightly below. Subject 2: Knee extensor and flexor torque increased following two weeks of exercise. Extensors increased from 25.5 to 38.9 Nm (+53%), and flexors from 11.6 to 17.1 Nm (+47%). After 15 weeks, a decrease occurred for both muscle groups, but torque was maintained above baseline. Flexor torque was 14.3 Nm (+23% above baseline), and extensor torque was 32.4 Nm (+27% above baseline).
DISCUSSION: Improvements occurred within the first two weeks of exercise for both subjects. There was a relationship between stage of disease and strength gains with exercise, with the younger subject demonstrating the greatest improvement. Over the following three months, strength decreased, but was maintained well above baseline values in the younger subject. It is important to note that a gradual decline in strength would be expected in a child with DMD. In contrast, resistive exercise was found to be of little benefit for improving muscle strength in the older subject. Exercise should begin relatively early in the course of the disease process. Strength will eventually decline in the child with DMD, but if the child develops a greater reserve of muscle capacity, it may be possible to maintain improved function for a longer period of time, thus improving overall quality of life. Further studies are needed to confirm the benefits of exercise for children with DMD, and to determine the ideal exercise protocol for specific stages of the disease process.