Muscle weakness, often seen in children with cerebral palsy, may be due to a variety of factors including: decreased central nervous system motor unit recruitment and discharge rates; increased antagonist coactivation during agonist contractions; or changes in muscle morphology, including atrophy. Until recently, clinicians would not advise muscle strength training in children with CP, due to the unsubstantiated belief that high effort voluntary contractions may promote increased muscle spasticity and tone. Recent studies have demonstrated that strength training in children with CP can improve gait speed, stride length, amount of knee flexion at foot strike and gross motor function. Furthermore, a systematic review of the literature concluded that strength training can improve muscle force production in children with CP without increasing spasticity.
Because children with CP are unable to fully activate their voluntary muscles as compared to typically developing children, the use of voluntary contractions for strength training may not produce sufficient force to induce muscle growth. Neuromuscular electrical stimulation (NMES), an alternative strength training technique, has been used successfully to treat adults with deficits in voluntary muscle activation. A recent study compared NMES to volitional strength training in a cohort of children aged 8 to 12 with spastic diplegic cerebral palsy to determine which group would experience greater gains in isometric force production, muscle cross sectional area (CSA) and walking speed after a 12 week program. Results indicated that NMES produced a significantly greater normalized force production for the both the quadriceps femoris and triceps surae muscles as well as a greater post training walking speed. The study also found that NMES produced greater changes in quadriceps CSA than the volitional group, but no significant difference was found between the two groups in the CSA of the triceps surae muscles.
These researchers are currently funded by NIH to conduct a randomized, controlled clinical trial comparing NMES to volitional strength training in a cohort of children with CP. Their specific aims are to compare the force generating, volitional activation, contractile and fatigue characteristics of leg muscles in typically developing children and children with CP; 2) to assess the ability of NMES strength training to increase leg muscle force-generating ability as compared to volitional strength training and a no-exercise control group in children with CP; 3) to assess the mechanisms underlying improvements in force-generating ability of the leg muscles after strength training in children with CP; and 4) to assess the ability of strength training to improve gross motor function and gait in children with CP. This work will help clinicians design rehabilitation strategies based on the physiologic differences in skeletal muscle and mechanisms for force production between children with CP and children of typical development. These researchers believe that there is great potential for NMES to be used in conjunction with volitional strength training and other motor learning therapies to help increase motor function in children with CP.
* Stackhouse SK, Binder-Macleod SA, Stackhouse CA, McCarthy JJ, Prosser LA, Lee SCK. Neuromuscular electrical stimulation versus volitional isometric strength training in children with spastic diplegic cerebral palsy: a preliminary study. Neurorehabil Neural Repair 2007;21:475-485.