biomechanics - spasticity

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How does spasticity affect Biomechanics?

In this situation, the spastic muscle contracts excessively and becomes shorter than normal. Because it is short, the muscle is weaker and less effective than a normal muscle. But this is not the end of the story. The overreacting spastic muscle also reflexively inhibits the antagonist muscle, on the opposite side of the joint from the spastic muscle. This results in an elongated, hypotonic, muscle that is even weaker than the spastic muscle.

In many children with spasticity the end result is a difficult situation in that both the spastic and the non-spastic muscle are weaker than normal, but the spastic muscles are actually the strongest ones in the child’s body. The unbalanced pull of the short spastic muscle is what causes the biomechanical problems in children with cerebral palsy and head injury.