Effects of Exercise: Humans
Modes of Exercise Studies on humans have been performed using active-assistive, active-resistive and isokinetic exercise, to determine whether exercise causes improvement or further deterioration in persons with DMD.
Vignos and Watkins studied the effect of a home exercise program with graduated weight for maximum resistance over 12 months on 14 patients with DMD. The program consisted of hip abduction, hip extension, knee extension, shoulder flexion, and sit-ups. Manual muscle tests were performed before, partially each month, and completely at the end of 12 months. Percent total strength present was determined from the complete muscle tests. Additionally, stair climbing, chair rising, rising from the floor, and walking a fixed distance was tested each month. Finally, the amount of weight that could be lifted was assessed.
The results of this study showed that persons with DMD made improvements in the amount of weight lifted at some point during the study. However, a slight decrease in the amount of weight lifted from the peak values recorded was seen by the end of the year in persons with DMD, but was still higher than initial values. The stronger the muscles were initially, the greater the strength gains that were made at some point during the study. Exercised persons with DMD were compared to unexercised one year before, and the year of the study. Both groups showed a decline in strength before the study. However, during the year of the study, the exercised group showed no loss of strength, while the unexercised group continued to show a decrease in muscle strength. A surprising finding was that the exercised group showed only an improvement in one out of 52 functional tests at the final evaluation.
Results of this study show that resistance exercise can increase strength in persons with DMD. However, no functional improvements were long lasting. This could be due to the non-functional resistance exercise that was performed. Exercises that mimic daily activities may be recommended in order to see improvements in functional tests.
Lateur and Giaconi studied the effect of controlled submaximal exercise in muscular dystrophy. Four children with DMD performed 30 concentric only contractions (knee extension). The exercise was performed on a Cybex isokinetic exerciser (18 degrees per second) four or five days per week for six months. The training torque produced by each child ranged from 0.5 ft-lbs. to 4.3-ft lbs.
The results of this study showed a slight but non-significant increase in torque of the exercised quadriceps compared to non-exercised quadriceps. Creatine kinase levels were not measured in this study, so muscle damage caused from the exercise cannot be determined. However, Boppart et al. used maximal eccentric isokinetic muscle contractions as the mode of exercise. A finding that was not discussed was that the maximal eccentric isokinetic contractions did not result in a significant increase in plasma CK in normal subjects. This type of exercise (isokinetic) may be the preferred mode for patients with DMD if exercise-induced muscle damage is to be limited or eliminated. The rationale for using isokinetic eccentric exercise is to prevent the damage that is associated with the dynamic-constant external resistance (machine, free weights). The elimination of muscle damage is necessary to prevent the muscle cell necrosis that is seen in persons with DMD.
The results of the above human studies suggest that persons with DMD who exercise can improve their muscular strength through resistance exercise. However, the mode, intensity, duration, and frequency have not been fully elucidated.