Exercise Literature on Cerebral Palsy: Resistance Training
McCubbin and Shasby studied the effects of a resistance training program on elbow extensor strength in 30 children and adolescents with different degrees of cerebral palsy who ranged in age from 10 to 20 years. Subjects were matched on type and severity of cerebral palsy using the classification system employed by the National Association of Sport for Cerebral Palsy (now called the National Disability Sports Alliance - NDSA). The investigators used two different training protocols: isokinetic exercise and repetitive movement exercise without resistance. Subjects in the control group continued their usual therapy in their respective schools. The treatment protocol consisted of exercising the tricep extensor group with three sets of 10 maximal speed repetitions, three times per week for six weeks. Subjects in the repetitive exercise group (no resistance) followed the identical training program as the isokinetic exercise group, except that the repetitions were completed without any resistance. The investigators found significant differences in speed of movement and time rate of torque development in the isokinetically trained group.
McCubbin and Shasby recommended further research: matching subjects on more variables (age, sex, etc.); collecting data over several repeated measures for both movement time and torque; varying the speed of isokinetic training; and using a single subject design to compare the effects of isokinetic training on the various types of cerebral palsy.
The application of resistance training throughout the full range of motion, coupled with the emphasis of rate of movement, produced a training effect in individuals with cerebral palsy similar to that found in exercise programs in non-handicapped subjects.
Holland and Steadward studied the effects of resistance and flexibility training on seven elite athletes with cerebral palsy. Their study also showed increased strength in all athletes in elbow flexion and extension. They also found quadricep/hamstring improvement for the three athletes who could walk. Flexibility showed improvement in active and passive range of motion, but active showed a greater increase. Fine motor tasks improved in six of the seven athletes. Their only caution was that all participants should stretch the major muscle groups of the upper and lower body before engaging in resistance exercise. They also noted that in their subjects, the wrists and ankles seemed to display less range of motion because these joints are rarely stretched.
Holland and Steadward noted that "athletes with cerebral palsy can participate in intense strength training programs without experiencing detrimental effects in flexibility and spasticity."
Olney and colleagues evaluated the work and power of major muscle groups in the affected limbs of 10 children with spastic hemiplegia. Cinematographic film and force-plate data were used to calculate the positive and negative workload around each joint. The investigators found that the force produced by the ankle plantar flexors during slow and normal walking speeds was different compared to healthy adults. In healthy adults, the ankle plantar flexors contribute nearly 66 percent of the total concentric work; the hip flexors and extensors are responsible for approximately 25 percent of the total concentric work; and the knee extensors the remainder. In children with cerebral palsy, the ankle plantar flexors provided only 33 percent of the total work of the affected limb.
Olney and coworkers concluded that the ankle plantar flexors on the affected side of children with spastic hemiplegia are severely deficient in generating power during walking, which resulted in greater amounts of work being done by muscle groups of the hip. They recommended that good range of motion at the ankle should be emphasized so that muscular contraction can be effective in generating power. In developing strength programs for persons with cerebral palsy, it is important to assess individual muscle groups to determine any asymmetrical weakness that may impose a greater burden on walking.
King et al. researched the feasibility of improving gait in children with cerebral palsy using a hip-extensor tricycle (with added weights). Their initial hypothesis was that if they could improve hip extensor strength, gait would improve. After working with their subjects on this specially adapted tricycle for 10 weeks, they saw no results in strength after testing them in two different ways. However, they did find an improvement in gait.
The specially built hip-extensor tricycle did activate hip-extensor muscles similar to walking, and to a greater extent than a traditional tricycle. The investigators noted that training on a device that promotes an upright movement pattern similar to walking probably improves motor control in gait. Although gait improved, hip extensor strength did not. The researchers used only five children with cerebral palsy. It would be interesting to determine if a similar adult-size tricycle could elicit improved gait in adults with cerebral palsy. Adaptive fitness technology for persons with cerebral palsy is something for the Task Force to consider over this two-day meeting.
In 1994, Kramer and MacPhail studied the relationships among measures of walking efficiency, gross motor ability and isokinetic strength in 17 adolescents with cerebral palsy. They reported that "adolescents with mild cerebral palsy could safely and reliably be tested for knee extensor and flexor strength during standardized isokinetic tests of concentric and eccentric muscle actions." They also reported that isokinetic equipment can be safely used with this population.
Kramer and MacPhail offered several recommendations for future research:
a) Determine if changes in muscular strength are reflected by changes in gross motor ability and walking efficiency;
b) Determine if individuals with cerebral palsy can respond to a strength training program without unwanted side effects; and
c) Evaluate how strength training programs might best be combined with neurological techniques.
The most important finding from the Kramer and MacPhail study was that there was a direct relationship between knee extensor strength and efficient walking and gross motor ability. They believed that lack of strength in the knee extensors could be one reason why adolescents with CP are limited in their standing, walking, running, and jumping activities. They stated that "improvements in muscular strength may be associated with improvements in walking efficiency and functional abilities in this population." There is a strong need to replicate this research on adults with cerebral palsy.
O'Connell, Barnhart, and Parks examined the relationship between muscular endurance and wheelchair propulsion in three children with cerebral palsy. Using a 6-RM test for elbow flexion, elbow extension; shoulder abduction, flexion, extension, internal and external rotation; and a combined shoulder flexion-elbow extension with cuff weights, dumbbells and barbells, their data showed that muscular endurance and both anaerobic and aerobic wheelchair tasks were correlated. They recommended that a muscular endurance program be developed for persons who use a wheelchair for ambulation, since there is a strong association with the ability to push a wheelchair and the amount of muscular endurance that a person possesses. They cautioned, however, that with such a small sample size, more research is needed on specific outcomes of muscular endurance training.
In 1995, O'Connell and Barnhart published a similar study using the same data set to determine if resistance training could improve wheelchair propulsion in pediatric wheelchair users. The three children with spastic cerebral palsy performed resistance exercises three times a week for nine weeks, using cuff weights, dumbbells and barbells. They performed three sets of 6-RM for each movement: elbow flexion and extension; shoulder abduction, flexion, extension, internal and external rotation; and a combined supine shoulder flexion-elbow extension.
Results indicated that progressive resistance exercise training appears to be able to improve muscular strength and wheelchair performance in children with cerebral palsy. However, the small sample size (n=3) and lack of control group warrants caution when interpreting the results. O'Connell and Barnhart did conclude, however, that "consideration should be given to use of a formal resistance training program to enhance and maintain wheelchair propulsion abilities. We may be under stressing these children and preventing them from achieving their full physiological potential."
In 1995, Damiano, Kelly and Vaughn studied the effects of quadriceps femoris muscle strengthening on crouch gait in 14 children with spastic diplegia. They wanted to determine if there was a causal link between resistance training and improved gross motor function. The subjects exercised three times a week for six weeks using ankle weights at loads of approximately 65% of maximum isotonic force production. Gait analyses were also performed before and after the study. The investigators found that the subjects were able to increase quadriceps femoris strength with resistance training, and that there was no increase in hamstring muscle force. They concluded: "our study focused on quadriceps femoris muscle weakness as one component of the motor dysfunction seen in children with CP, and utilizing a traditional orthopedic approach rarely recommended with this population demonstrated clinical improvement in strength and ambulatory ability." However, they cautioned that several of the children developed knee hyperextension in mid-stance, which prompted the investigators to recommend the possibility of hamstring strengthening at the same time that the quadriceps are developed.
They made the following recommendation for future research: "Although strengthening is an effective treatment option in CP, more evidence of functional improvements due to strengthening that have a significant impact on the quality of life of these children needs to be produced through the use of motion analysis or other objective outcome measures prior to widespread advocation of this approach in the clinic."
Damiano, Vaughn and Abel continued their research and examined the muscle responses to heavy resistance training in children with cerebral palsy. They compared their findings to a control group of 25 children who did not have a disability. The investigators found that "all children [with cerebral palsy] who participated in the study had consistent and dramatic strength increases in the quadriceps muscle, with the majority attaining normal strength values. A concurrent increase in the strength of the hamstring muscles was not found. This eliminated the concern that heavy resistance exercise would elicit unwanted muscle activity in antagonistic muscles. The researchers also reported that quadriceps strengthening improved "knee extension in terminal swing, as indicated by significantly less knee crouch at initial floor contact and increased stride lengths at free and fast walking speeds."
The investigators made the following recommendations:
a) a more comprehensive lower-extremity strength training program involving several muscle groups might produce greater functional improvements;
b) the biomechanical and physiological implications of weakness and muscle imbalance in spastic cerebral palsy need to be better understood;
c) precise quantification of the pattern and magnitude of the weakness is needed; and
d) there should be "objective" documentation of change produced by interventions that positively or negatively effect strength.
In their most recent study, Damiano and Abel expanded their research to examine the effects within and across two distinct clinical subgroups: children with spastic hemiplegia (n=5) and children with moderate to severe spastic diplegia (n=6). The children ranged in age from 6 to 12 years. The investigators wanted to determine if a resistance training program would increase strength in certain targeted muscles. The untrained muscles were used as a basis for comparison. In the children with hemiplegia, strength changes on the more affected extremity were compared to corresponding muscles on the contralateral extremity. In the children with diplegia, the ipsilateral antagonist muscles were used as the untrained comparison. Eight muscle groups were tested using a hand-held dynamometer.
A secondary purpose of the study was to determine if subjects could achieve functional gains in performance after the resistance training program. Computerized gait analysis was used for this purpose. Subjects were asked to exercise three times a week for six consecutive weeks. Velcro-attached free weights were used, and the load for each muscle was approximately 65 percent of the maximum isometric strength value. Each subject performed four sets with five repetitions in each set at each muscle group.
Results of the study found that in the children with diplegia, there was a 69 percent increase in strength after training in the targeted muscle groups, and in the children with hemiplegia, there was a 20 percent increase. Functional changes were also found for the entire group. Subjects increased their maximal speed during fast walking.
Damiano and colleagues reconfirmed the findings of previous research that resistance training in young individuals with cerebral palsy is safe and effective in improving strength and motor performance: "to our knowledge, there is no research to support the theory that resistance training increases the recruitment of other muscles that are already overactive or spastic, which would obviously be contraindicated if this were the case."
In their most recent article (1998) on resistance training in children with cerebral palsy, Damiano and Abel concluded that a short-term strength training program demonstrated positive functional outcomes. They also reiterated that the clinical concern that resistance training will cause an "inadvertent strengthening of the spastic antagonist muscle during training" is unfounded.
MacPhail and Kramer tested the effects of isokinetic resistance training on functional ability and walking efficiency in 17 adolescents with cerebral palsy. Their eight-week strength-training program yielded noteworthy results. The adolescents showed significant increases in knee extensor and flexor strength as a result of training. They also reported that the children with diplegia, and one subject with quadriplegia, when given the opportunity to participate in joint-specific muscle strengthening independent of their ability to balance in standing, were able to respond with substantial increases in strength. They concluded that "muscle capability of adolescents with mild cerebral palsy is relatively normal." They found no increased spasticity resulting from the strength training program.
They recommended the following ideas for future research:
a) Determine the actual mechanism of strength gains;
b) Evaluate the optimal frequency and duration of strength-training programs;
c) Investigate the practicality of resistance training for other lower-extremity muscle groups such as the ankle plantar flexors and dorsi flexors; and
d) Establish criteria for appropriate selection of subjects who can safely participate in such programs without unwanted side-effects.
"No scientific evidence exists to support the clinical prejudice against strength testing and training for individuals with cerebral palsy or other upper motor neuron disorders. In fact, research findings are accumulating that indicate that children with cerebral palsy are indeed weak, that strength is related to motor function, and that isotonic and isokinetic strengthening programs can result in functional improvements."