ABSTRACT
Direct demonstration that evaluation of spasticity at rest has little relevance for the situation during movement was originally provided by Ibrahim et al. They measured stretch reflexes in elbow flexors of healthy subjects and on the lesioned and non-lesioned sides in hemiplegic stroke patients at rest and during voluntary elbow flexion. The depolarisation necessary to activate the motoneurons during a contraction naturally also makes them more excitable to the input from stretch reflex afferents. The gain of the stretch reflexes is also increased in healthy human subjects by increased release of transmitter substances from the sensory afferent synapses on the motoneurons. A contributing factor to the depolarisation of the motoneurons is the removal of inhibitory inputs to the motoneurons. The functional significance of transcortical nature long-latency responses and thus the functional significance of their absence in patients with central motor lesions is not fully clarified.
