Intensive repetitive motor training: how does it work in children with cerebral palsy?

Abstract

Intervention approaches for neurodevelopmental disorders often draw from the knowledge, experience, and ideas developed from rehabilitation of adults with acquired brain injury. Among those interventions, intensive repetitive motor training has been successfully adapted, particularly in management programmes for children with cerebral palsy (CP). Further discussion is required about goal setting, involvement of caregivers and professionals, feasibility in some settings, use of mechanical devices, effective dosage, personalization of the programmes, and relevant integration within wider intervention planning. Meaningful clinical improvements have been documented and more studies are underway. The assumption that those improvements reflect structural changes has been partly verified, but the literature is scant and still difficult to interpret. But the hypothesis of experience-dependent plasticity of the motor system is appealing, even more so in the developing child. Ongoing and future studies may help clarify issues and optimize the design of programmes. In addition to the key features mentioned above, these studies should consider factors relating to force generation and endurance, level of the effort, time variation in muscle length and tension (isometric, isotonic, concentric, eccentric contraction), biomechanical degrees of freedom, sensory input, requirements for cognitive processing, and coordination, as well as other aspects of movement and postural control. In typically developing individuals, training has been amply documented to make muscle activation more effective following motor command. This has been related to both muscle and neural reorganization. Repetitive neuromuscular activity may have trophic and maintenance effects on muscles, peripheral and central neurons, glia, and other structures through a host of signalling molecules. Increase in muscle fibre volume is associated with enhanced contractility and potential for modulation as well as mechanical effectiveness (e.g. greater fibre pennation angle makes the contraction more powerful). More profound changes in the anatomical and physiological properties of skeletal muscles might also occur. Moreover, training might alter the mechanical properties of tendons. All these possible effects are expected to impact the muscle-tendon unit, which has received relatively limited attention to date in CP. Promoting neuroplasticity is often mentioned as a rationale for intensive repetitive motor training in children with CP. This might also include spinal circuits and deep brain structures, but the main target appears to be the cortex, with support from a few neurophysiological and neuroimaging studies. Cortical changes associated with intensive motor training in adults without motor impairment show some inconsistencies, ranging from reduced to increased markers of connectivity within brain areas relating to the task; from reduced to increased activity in those areas during the execution of the task; and combinations of reductions and increases. In this context, decreased cortical activation could be interpreted as a gain in neural efficiency, implying that less neural energy (or perhaps computation) is required after intensive repetitive motor training. Training of certain tasks might thus allow higher degrees of automatization and shift motor control to memory-based processing by reorganizing the cortical representations of sensorimotor features. Such reorganization has been suggested following intensive training in adults with stroke and a few children with CP. But limits to our current understanding of the underlying mechanisms challenge interpretation of increase and decrease of the studied cortical indices within selected brain areas. Analyses on a network level may prove to be more relevant, particularly in neurodevelopmental disorders. Of course, it is essential to realize that changes in body structures or function do not necessarily predict change in activity or participation. Therefore, further development and understanding of intensive repetitive motor training for children with CP makes sense only if each patient’s specific goals can be identified and serve to design activity-based therapy with measurable, meaningful outcomes in real life.