Muscle compliance: implications for the control of movement

We suggest in this review that compliant properties of the neuromuscular system influence and must be considered at every level of motor function. These properties emerge from the combined operation of many physiological mechanisms. At the behavioral level, no aspect of the compliant response can be attributed to muscles or reflexes alone. Furthermore, for all but the slowest movements, all three mechanical properties must be taken into account. Although we have considered only reactions to external forces and the implications for normal voluntary movements, there are many other areas of relevance that we have not discussed. In particular, clinically important problems such as the control of orthotic/prosthetic devices, functional electrical stimulation, and the effects on muscle tone of neuromuscular pathologies like Parkinsonism are all issues in which compliant behavior is either the cause of problems or must at least be well characterized to allow successful treatment. These are all issues worthy of further study.