Consequences of an upper motor neuron syndrome (UMNS) include voluntary weakness or paresis, superimposed involuntary phenomena such as spastic co-contraction and associated reactions, and superimposed rheologic changes in affected muscles. This article describes the use of dynamic poly-electromyography to assess UMNS muscle overactivity and inform muscle selection for chemodenervation. Cases are presented that involve spastic co-contraction, spastic dystonia, associated reactions, hyperextended wrist and finger flexor tenodesis, differentiating neural versus non-neural (rheologic) hypertonia, upper motor neuron weakness, muscle selection for chemodenervation, and electrical stimulation for muscle specific targeting.